1998 Chevy Monte Carlo EGR problem?

Check engine light on and flashing ?
I would suspect a tune up and or bad coil check for DTC s codes
check if have spark on each and every cylinder check at the coil side
check fuel pressure

its not flashing, it was on constant, I just reset it by unplugging the computer for 10 minutes. Now theres no code for anything in thaere, the car starts and idle, but still I can't rev it over 2500 RPM, it just sputters like nuts. I can hold it at 1800 RPM no problem without a single misfire.

How would I go about checking the fuel pressure? I have a compression tester I borrowed from autozone.

I would think it was a spark problem, but it idles fine just misfired on ALL cylinders if i try to bring the RPMS up. Even when I press the gas to bring the rpms up and it sputters hard, no codes get stored.

I'm kinda new to working on the internals of a car's engine so more specific help would be nice, like how to go through checking these things out.

Thank you.

our video collection should help in showing you how some things can be checked

https://www.2carpros.com/car_repair_video/how_to_scan_your_car.htm

https://www.2carpros.com/car_repair_video/test_fuel_injection_pressure.htm

https://www.2carpros.com/car_repair_video/test_engine_ignition_system.htm

ok i found the fuel pressure testing port and used a fuel pressure tester to check the pressure.

It was at spec, 40 or close, the test kit says 41-47PSI is my spec. it was at 40 even when key off, jumped to 45-46 when priming, then dropped back to 40. with the engine running it dropped to about 35-37 psi with the fuel regulator vacuum in effect, if I removed the hose from the fuel regulator it would jump to 48 PSI.

if I leave the test gauge connected after about 2 hours the pressure dropped down to 10psi, but immediatly jumped to 46 psi when i turned the key to activate the pump again.

I thought everything seemed good tho the values displayed were about 1psi under spec.

When i pull the throttle slightly it drops alittle pressure, and is about the same pressure when at 2k rpm as when it starts misfiring at 2500 rpm, tho the pressure flucuates about 1-2 psi less when it was under load.

Does any of this indicate a fuel problem? one that would cause my engine to completely misfire over 2500 rpms?

It still idles perfect while cold, I'm stumped on where to check next.

No engine codes even tho it misfires and almost dies when I try to get it above 2500 rpms.

I remember the first time I had it scanned something showed up about a Fuel Evaporation Canister error of some sort, Could this be something that is causing this problem? I just read a post somewhere about an Isuzu rodeo that wouldn't rev over 4k rpm, would just misfire. Someone suggested the evaporation canister solenoid. Could this be my issue?

Or could it possibly be the catalytic converter catastrophically failed on me?

still strange I get no codes

Evap system will not cause a misfiring
if have check engine light on you should have a code s
it could be a lot of things have to start with the basic check

fuel pressure ,spark on all cylinders ,codes
compression and timing

I don't have a check engine light on, I cleared it the other day hoping that the computer just needed to be reset after I cleaned the EGR system out.
I unplugged teh battery cable for 15 minutes then plugged it back in. No new codes have been stored.

My fuel pressure is ok I think, I described the reading I got.

I'm getting spark on all cylinders because it idles smoothly.

I don't know how to check my timing or compression.

Could my timing be off? That wouldn't effect my idle or lower rpm running ability?

it purrs like a kitten up to 2500 RPM then it misfires constantly and won't go higher.

Fuel pressure checks out and no codes are storing, tell me where to go next.

I took the ICM and ignition coils into autozone to have them tested, I got 0 resistance on tests on all 3 coils, and the ICM passed their test.

What about the fuel pressure ?

The fuel pressure was ok. it was within spec i believe, 40 psi with the car off, 47 psi when pump was priming, dropped a bit when engine idled, drops maybe 1-2 psi more when its under load, stays pretty consistent when misfiring but flucuates maybe 1-2 psi.

I read that good fuel pressure doesn't always mean it has enough flow. If i press the gas in hard it misfires immediately as opposed to if i push it gradual it will climb to 3k rpms, I cleaned the MAF and now i get abotu 500 more rpm out of it.

I finally got the fuel filter off, the old one was pretty grimy, thick black crap poored out of it then it went completely clogged, I put a new filter on but same symptoms.

i pulled a p1676 code off an OBDII scanner, any idea what this is?

I read somewhere someone mention about the brake booster, could my problems be from vacuum failure in teh brake booster? I noticed when i first started the car that my ABS would kick in when i hit the brakes coming to the end of my driveway at like 5 mph.

I jotted down some values from the freeze data, the car wasn't running when it threw the code, at least it said 0 rpms,

MAP sensor at 99 KPA

Short term fuel trim 1 0.8%
Long term fuel trim 1 0.8%
Short term fuel trim 3 -96.7% (is that normal?)
Long term fuel trim 3 8.5%

DTC P1676 - EVAP PURGE VALVE CONTROL CIRCUIT

The Output Driver Module (ODM) is used by the PCM to turn on many of the current-driven devices that are needed to control various engine and transaxle functions. Each ODM is capable of controlling up to 7 separate outputs by applying ground to the device which the PCM is commanding on. ODM have the capability of diagnosing each output circuit individually.
Conditions required to set DTC are:
Ignition is on. • Improper voltage level detected on output circuit controlling EVAP purge solenoid valve. • Conditions present for at least 30 seconds. •
Diagnostic Procedures
Circuit Description

Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK , then go to next step. Turn ignition off. Disconnect PCM connector. Turn ignition on. Using DVOM, check voltage between ground and EVAP purge valve control circuit at PCM connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6). Set ammeter to 10-amp range. Check current between ground and EVAP purge valve control circuit at PCM connector. Monitor reading for a minimum of 2 minutes. If current is .05-.50 amp, go to step 11). If current is not .05-.50 amp, go to next step. Disconnect EVAP purge valve connector. Using DVOM, check voltage between ground and EVAP purge valve control circuit at harness connector. If voltage reading is zero volts, go to step 10). If voltage reading is not zero volts, go to next step. Locate and repair short to voltage in EVAP purge valve control circuit. After repairs, go to step 16). 5. Turn ignition off. Remove and inspect fuse for EVAP purge valve. If fuse is blown, go to next step. If fuse is okay, go to step 8). Locate and repair short to ground in ignition feed circuit for EVAP purge vent valve. Replace fuse. After repairs, go to step 16). Disconnect EVAP purge valve. Turn ignition on. Check voltage between ground and ignition feed circuit for EVAP purge valve harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13). Check for an open or short to ground in EVAP purge valve control circuit. Repair as necessary. After repairs, go to step 16). If circuit is okay, go to next step. Check EVAP purge valve control circuit and ignition feed circuit for poor terminal connection at EVAP purge valve and at PCM connector. Repair as necessary. After repairs, go to step 16). If connections are okay, go to step 14).

Turn ignition off. Reconnect PCM harness connector. Disconnect EVAP purge valve connector. Turn ignition on. Connect a test light between EVAP purge valve control circuit and ignition feed circuit terminals at EVAP purge valve connector. Using scan tool, select OUTPUTS TEST function and cycle EVAP purge solenoid on and off. If test light flashes on and off, see DIAGNOSTIC AIDS. If test light does not flash, go to next step. Check EVAP purge valve control circuit for poor terminal connection at PCM. Repair as necessary. After repairs, go to step 16). If connection is okay, go to step 15). Locate and repair open in ignition feed circuit to EVAP purge valve. After repairs, go to step 16). Replace EVAP purge valve. After replacing valve, go to step 16). 14. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step. Using scan tool, select CLEAR INFO or CLEAR DTCS function to clear DTCs. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. Monitor SPECIFIC DTC info for this DTC until this DTC test runs. If scan tool indicates FAILED THIS IGN, repeat step 2). If scan tool does not indicate FAILED THIS IGN, repair is complete.

It isn't really clear what each step is in that description.
I can't figure out what step 6 is, etc...

TESTS W/CODES - 3.1L -1998 Chevrolet Monte Carlo

NOTE: For circuit reference, see WIRING DIAGRAMS - 3.1L article.
DTC P1676 - EVAP PURGE VALVE CONTROL CIRCUIT

Circuit Description
The Output Driver Module (ODM) is used by the PCM to turn on many of the current-driven devices that are needed to control various engine and transaxle functions. Each ODM is capable of controlling up to 7 separate outputs by applying ground to the device which the PCM is commanding on. ODM have the capability of diagnosing each output circuit individually.
Conditions required to set DTC are:
Ignition is on. • Improper voltage level detected on output circuit controlling EVAP purge solenoid valve. • Conditions present for at least 30 seconds. •

Diagnostic Procedures


1.Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK , then go to next step.

2.Turn ignition off. Disconnect PCM connector. Turn ignition on. Using DVOM, check voltage between ground and EVAP purge valve control circuit at PCM connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 6).

3.Set ammeter to 10-amp range. Check current between ground and EVAP purge valve control circuit at PCM connector. Monitor reading for a minimum of 2 minutes. If current is .05-.50 amp, go to step 11). If current is not .05-.50 amp, go to next step.

4.Disconnect EVAP purge valve connector. Using DVOM, check voltage between ground and EVAP purge valve control circuit at harness connector. If voltage reading is zero volts, go to step 10). If voltage reading is not zero volts, go to next step.

5.Locate and repair short to voltage in EVAP purge valve control circuit. After repairs, go to step 16).

6. Turn ignition off. Remove and inspect fuse for EVAP purge valve. If fuse is blown, go to next step. If fuse is okay, go to step 8).

7. Locate and repair short to ground in ignition feed circuit for EVAP purge vent valve. Replace fuse. After repairs, go to step 16).

8. Disconnect EVAP purge valve. Turn ignition on. Check voltage between ground and ignition feed circuit for EVAP purge valve harness connector. If battery voltage is present, go to next step. If battery voltage is not present, go to step 13).

9. Check for an open or short to ground in EVAP purge valve control circuit. Repair as necessary. After repairs, go to step 16). If circuit is okay, go to next step.

10.Check EVAP purge valve control circuit and ignition feed circuit for poor terminal connection at EVAP purge valve and at PCM connector. Repair as necessary. After repairs, go to step 16). If connections are okay, go to step 14).

11.Turn ignition off. Reconnect PCM harness connector. Disconnect EVAP purge valve connector. Turn ignition on. Connect a test light between EVAP purge valve control circuit and ignition feed circuit terminals at EVAP purge valve connector. Using scan tool, select OUTPUTS TEST function and cycle EVAP purge solenoid on and off. If test light flashes on and off. If test light does not flash, go to next step.

12.Check EVAP purge valve control circuit for poor terminal connection at PCM. Repair as necessary. After repairs, go to step 16). If connection is okay, go to step 15).

13.Locate and repair open in ignition feed circuit to EVAP purge valve. After repairs, go to step 16).

14.Replace EVAP purge valve. After replacing valve, go to step 16).

15. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step. Using scan tool, select CLEAR INFO or CLEAR DTCS function to clear DTCs. Turn ignition on, with engine off.



16.Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. Monitor SPECIFIC DTC info for this DTC until this DTC test runs. If scan tool indicates FAILED THIS IGN, repeat step 2). If scan tool does not indicate FAILED THIS IGN, repair is complete.

I just replaced the spark plugs and wires as my plugs were old.

I took it out on the road to try to get a code to throw. I noticed if I tried flooring it it would miss immediately, if I drive like normal it goes fine unless I get to 3k RPM then it starts misfiring.

I noticed in O/D that it starts to miss alot aooner, like 2k rpm, and it misses alot harder, like the car jerks.

when testing the MAF with a DVOM what exactly am i checking for? there are 3 wires to my MAF, a yellow one on the left, a black one witha white strip in the middle, and a red one on the right. Which one do I want to check? I tried myself and one of the wires read 4.53V at idle, and dropped down steadily to 4.0V when i increased teh throttle to about 2500 RPM. I didn't test the black wire witha white line in it, the other wire read 14V so im guessing that was the power feed.

ok so I just figured out my s-10 has the same MAF sensor, So I took the sensor off my s-10, cleaned it, and put it on my monte carlo. I started it up, the injectors were pretty loud, but they usually are when I first crank it. Then I ran a bit, it misfired alittle but then it started making it to 4k rpm, and the rev limiter, So I took it on the road and punched it, it worked fine, I drove down the road with the occasional hiccup but it climbed to 6k RPM then cruised at 8- mph fine. I turned around to come back, and punched it again, and then it started missing again and I'm right back where I started. I don't know if it was working good because the engine was really cold or what, It threw no dcodes and now I'm back to where I started, I'm so confused and disapointed with the false hope I was given.

any ideas?

Ok I ran it a bit more and got the original symtoms again, except worse. I went about 4 miles to the gas station, when I pulled in, it died. I put 5 bucks in the tank then I was gonna ride softly to autozone since at lower rpms it seems to be fine, well not now. I pulled out of the gas station and it started bucking at around 1500 rpm, the tach would drop and jump all over the place. So I turned around and drove home. Even with my foot off the gas and cruising it would want to die, the tach would drop 500-600 rpm and I still couldn't get it to go over 2500 rpm, also when I pressed the gas sometimes it would seem to do nothing, Obviously this problem gets worse the more warmed up the car is, and first thing in the morning with dew on the car it managed to get to 6k rpm. I read somecodes and got a new freeze frame data from when i unplugged the MAF I think tho I may be wrong, heres the info it put out tho.

MAybe its an electrical wiring problem? I don't know.

p0102

Load 1.1%

2610 RPM

MAP sensor 37 KPA

Air Flow Rate 1.90 GR/sec

Throttle position 16.4%

Coolant temp 197 degrees.

Fuel trim same as above

Fuel system open.

If I goto I/M monitor it says OK or N/A or INC, no fails.

It threw p1676 again as well I guess I need to check that wiring as well.

Hope some of this helps, and someoen can figure out what -96.7% short term 3 fuel trim is.

I got another p1676 code so I'm really starting to think this has something to do with fuel tank vapors constantly flowing into the vehicle maybe?

I noticed my fuel trim hasn't changed in this code, I read that the PCM doesn't adjust anything untill the engine goes into closed loop? So why would my engine not meet closed loop requirements?

Sorry I lost you some time ago !!!

disconnect the MAF sensor and try running it with it disconnected and if its better
suspect and replace it
S10 sensor may look the same but different # my be different check with local part store if they are the same
or not

Subject: 98 monte carlo wont exceed 2500 rpm
how do I perform a test with a scan tool? Or do I need a better scan tool?


what kind of scantool are you using ?
or is it an OBDII reader that you have

Just an OBD II reader that i borrowed from autozone.

I've been reading up a bit and I don't think my car is going into closed loop.

Every time I read freeze frame data from any code, my fuel trim is exactly the same. It hasn't tried to adjust it at all.

My thermostat appears to be working because the coolant temperature is different in each freeze frame and its been as high as 197 degrees, I'm not sure how to ttell if the car has gone into closed loop or not?

Possibly my o2 sensor is bad, I pulled it out to check if I was having an issue with backpressure from a bad cat and sprayed it with MAF cleaner and stuff, ran the car with it out confirming that the cat wasn't clogged as it ran the same with no backpressure.

in the freeze frames it says "FUEL system open" does that mean I'm still in open loop? That is the same on every code I scan as well.

I'm under the impression at some point my car set some really off fuel ratio information, then got stuck in open loop and has been using that information ever since and not going back into closed loop.

I don't know just throwing it out there.

I was doing the EVAP purge valve circuit fix and I was getting 0 amps on the connector at the PCM, and did get voltage at the connector to the purge valve(I think its the purge valve, it's located above the o2 sensor below the ICM on the back of my engine?) and I got voltage there. So I think it's leaning towards a short or a bad purge valve maybe? but i don't think that has to do with my engine going closed loop does it? I blew the fuse to the purge valve by trying to test amps on the power feed wire on the connector to the purge valve, so I'm getting good amperage there lol.

sorry just shooting some stuff out there to see what you think.

OK i Just took it out on the road, and got a p0401 code, EGR FLOW INSUFFICIENT.

I got this error a few times before, so I used carb cleaner and cleaned the EGR vacuum out best I could, and got a new EGR valve. Ok now I took the throttle body off (that was a pain due to a very poorly designed mounting bolt on the bottom right of the throttle body), cleaned the EGR out VERY good from the inside of the intake plenum, cleaned my throttle body out as well.

Unfortunately at some point while my throttle body was off I broke my throttle cable so now I need to replace that, any ideas? I musta kinked the wire or something because one tiny wire of the braided cable broke and started jamming up the cable so it wouldn't go back to idle, I tried pulling that off but 6 braided cords later its hanging by a single braid of wires and it still jams up so not much I think I can do other than replace it. I couldn't find an OEM replacement tho, just a universal kit? any suggestions?
Freeze Frame data:

------------------------------------------------------------

Throttle Position - 0.3%

Engine RPM - 1136

Air Flow Rate - 4.67GR/sec

MAP Sensor - 30 KPA

Coolant Temp - 177 degrees F

Short term fuel trim 1 - 0%

Long Term Fuel Trim 1 - negative 13.3%

Short Term Fuel Trim 3 - 50%

Long Term Fuel Trim 3 - negative 45.2%

Vehicle speed - 45mph

Fuel System 1 - closed

------------------------------------------------------------

So It finally went into closed loop and tried to adjust, but it was still misfiring. Note I took this drive with the evap purge valve unplugged. I was trying to go through the OBD II GM driving cycle I read but i didn't have enough space

I did the repairs and it said to replace evap purge valve. One thing that was weird is when I started the tests the connector at the PCM read battery voltage, but now after I've done all the tests If i goto read voltage at the PCM connector I get none? but I still get battery voltage at the purge valve connector.

Well im going to get a purge valve tomorrow but I doubt that will fix my problem, but I feel like I accomplished something getting rid of the codes I've been getting.

Also I was a little confused and I tested the voltage of the purge valve circuit while the PCM connector was connected and got 0.06 volts, whereas I get 0 volts with the connector disconnected. I believe I was supposed to test with the connector disconnected right?

So now that I fixed my EGR problem and my Purge valve problem where do I go from there? I'm still misfiring badly at 3k rpm.

Could something more internal like a fuel injector or piston be messed up? could my block be cracked, i'm lost at what to do now

After reading all this. I see your car revs fine up to about 2500rpm's. Have you checked your TPS? sometimes when they go bad it won't throw a code. But as you open the throttle the pot will reach bad spot and jump all over the place causing backfiring, hesitation and misfires. Maybe that's something to check out. If that scanner you have can graph the TPS slowly open the throttle as steady as you can and watch the graph. It should be a smooth line moving up. When you reach a bad spot the line will start jumping around.

I did compare parts at a few online stores for the MAF sensor to confirm that the s-10 and my car have the same MAF sensor.

on the TPS it isn't always at 2500 RPM, If I try flooring it it misses bad right off the get go and almost dies long before 2500 rpm, if I gradually apply throttle I can get to 3k rpm.

The car will die while idling sometimes when it is warmed up. I think it's more than a faulty sensor. It runs like this in closed or open loop.

I'm starting suspect fuel flow is the problem, I'm not sure if my fuel pressure is supposed to be 41-47 while running, or if its supposed to be a bit lower? I get 36 psi while running, I noticed if I rev up the engine then let off the gas the pressure drops down to 30 psi momentarily before building back up to 36.

I don't have any rfeally fancy equipment just stuff I borrowed from autozone.

I'm afraid to bring it to a shop because I worry they migh just go and replace tons of stuff before solving the problem, costing me way too much money.

I'm laid off right now and money is really tight.

Ok heres what we know, I think.

It's not the o2 sensor because it runs bad in open loop as well as closed loop.

It's not the catalytic converter because with the o2 sensor removed and the back pressure released it still runs the same. Same goes for backpressure released through removing the EGR valve.

It's not the MAF sensor because I replaced it with the same part number from another vehicle and it didn't make a difference. Also noting with the MAF unplugged it behaves differently but it's hard to tell with the problem being so severe as it is. it still idles fine without MAF hooked up.

It seems to be a problem isolated to 1 side of the Fuel trim? I'm not sure if the 2 sets of fuel trim refers to a trio of cyclinders or what? But Fuel trim 1 is always pretty normal, whereas fuel trim 3 is very far off? This has to mean something, most likely that that set of cyclinders has an air/fuel ratio problem.

This leaves us with a) not getting enough fuel flow to one half the engine. B.) not getting good ignition off one half the engine. C) bad injectors or bad compression on one half of the engine.

Well does any of that seem to make sense, maybe I'm wrong about the fuel trim, but it seems this problem is happeneing on half the engine, causing issues with the fuel/air ratio there and the computer struggles to fix it but it is far too severe.

so maybe my fuel injectors on that half are bad, that fuel rail is clogged or faulty? I don't know, what do you guys think?

It doesn't really mater if i remove sensors or not, it still runs like crap when you rev it. I really think my fuel injectors are bad or some of the cylinders have bad compression.

And how do I go about replacing this throttle wire?

ok scratch the throttle cable, I went to the hardware store and made my own.

Ok about the fuel trim, Since bank 3(there is no bank 2) is the one thats out of whack when the computer tried to fix it, thats obviously the side of my engine that is having problems probably, either bad injectors or something right? If my fuel pump wasn't putting out enough flow then both sides would probably have issues, If it was due to injection and I had a bad coil or something, then itd be one cylinder on each side.

This leaves me to believe I have bad compression on one of the cylinders of bank 3, or the fuel injector back there is bad or something along those lines.

So What Is my next step, or could it still be too little flow from the pump or a clogged fuel rail.

I still have decent engine fuel pressure I will pick up a vacuum guage and compression tester ASAP to test the back cylinders or the front ones, Im not sure what side TRIM 3 applies to.

can you walk me through how to test compression and/or vacuum? and where can I find the proper specs?

Could a bad injector or low compression be causing these problems mainly only at 2500 rpm or higher?

Ok the egr system is fixed, I ran a test drive and the I/M monitor says EGR system OK. On my test drive I had no codes but many symptoms. I got out on the road and took off gradually like the GM OBD II drive cycle says, Got up to 55mph and put on cruise control and drove 4 miles or so at 58 mph. I then gradually decellerated down to 20 mph, turned around and this time applied about 3/4 throttle and it was misfiring badly in the 2.5k-3k range, never got higher than that. I then got up to 55mph and re-equipped cruise control, it went a little bit, then it bucked alittle bit, kicking cruise control off. I traveled back to my house then cruised down to a stop at my driveway. It bucked a few more times on the way in.

I noticed that went it bucks the tachometer goes from liek 2.5k rpm down to 2k then flucuates some more before the car stops bucking and missing and settles down to slowly resume acceleration again. any of these driving symtpoms help anyone diagnosing the source of my problems?

I dont see how is it bucking with out turning the check engine light
on
check for pending codes
are you sure its an engine problem and not tranny issue
but again that should get a check engine light on
have a helper drive as you watch data on the scanner
checking misfire and tranny shifting data

could it be that the plate the coil packs are sitting on has a crack and only seperates when the car is warm andthat is why the coil packs came back fine?

I just wanted to add, you do have a bad fuel regulator. No doubt. When you turn your car off, the fuel pressure should not drop that low. (No more than 7-10 PSI from where it is when the engine is running)

But this is not to say that's causing your misfire. A leaking fuel pressure regulator causes your engine to run very rich which could foul your spark plugs and cause a misfire, but maybe in your case, maybe not.

Pull the vacuum line on the FPR and smell for gas. If there's ANY, then I'd bet that is causing your misfire. If not, then your FPR is bleeding the gas back to the tank when you shut your car off. Which it isn't supposed to do. Change the FPR anyway.

Now, I do believe either you have a bad Crank/Cam sensor, or your computer is bad. If you really would like to learn the ancient ways of an automotive technician, get a multi-meter and back-probe your sensors and the computer.

Check for reference voltages going to all of your sensors and fuel injectors as well as the voltages going back to your computer.

If any of your sensors aren't RECEIVING the right reference voltage, then either your wiring harness/connectors are corroded or broken, or the computer is bad. If any one of your sensors aren't SENDING their correct voltage to the computer, then the sensor is bad, or the wiring harness/connectors are corroded or broken.

Hopes this helps.

I have a 1998 Monte Carlo with 135,000 miles on it. I had issues with the Fuel Injectors years ago. Shuttering and shaking. I had one replaced and it was really expensive. Intially I was using Mobile Gas when I started having the problem. My husband didn't believe me when I said don't use the gas from that station anymore so he did and it messed my car up again and had to take it back to the shop. Had to take it back again because others were misfiring to. They put in fuel injector cleaner and I was told to use Shell Gasoline and I haven't had any problems since. For many many years. Only problem is my check engine light goes on all the time because of misfires. It has for years but the car is great and

Have you car's engine computer scanned for trouble codes to locate cylinder that is misfiring or if it is a sensor that is out of range.