Rough Running Engine

I have a 1993 Chevy Silverado regular cab that is lifted 9 inches, has 435 front and rear end, a 5 speed manual, 38inch tires, and a crate 350 4bolt main with maybe 50,000miles..

Keep in mind that it has been sluggish for 4ish months and I have replaced Plugs, wires, cap, router bug... But it has been sluggish and not quick to get up and go like it should when you mash the gas pedal. It's kinda delayed...

Anyways, I was driving down the interstate and I down shifted about 70-75 mph from 5th to 4th and I did so to get some rpm's and speed to get around someone and my tach never went about 4000rpms.. but it started to kinda tick and maybe have a little bit of a knock. Well when I got to my destination it was running pretty rough and it definitely shook everything inside the truck at idle from how rough the engine was running. I managed to make it to my apartment and never lost oil psi and it never began to smoke. I've done some research and it almost sounds like a Knock Sensor went bad cause of the previous sluggishness.. But I wanna know what someone else thinks.. Please.

Ok, um two codes came up: one pointed to the "environmental regulator", saying it was not working (we had to bypass it when we put in the propane system) and the other code came up as the "fuel regulator" which we had checked and cleaned on both the propane and gasoline systems.

Side note: my father recommended checking the silicon compound on the ignition module...the idea being if the module got too hot and there was little/no silicon, the lack of heat distribution would burn up the part and shut down the engine. Or the computer would read the problem, and kill the engine. When I checked the part, it does indeed lack the silicon on the metal plate...it had dried out and flaked off a long time ago.

Thank you for the donation, alright. lets see what you got going on.

Since i assume its distributed i would definitely check and set the ignition timing and make sure it is spot on and that it is advancing properly.

Next step is what type of fuel system. and what fuel pressure you got?

I would first get a scan do to check for any unresolved fault codes, a faulty knock sensor will trigger a code, I would also do a precautionary comp test, just to make sure all is good in that department, start here.

Unsure if there is an EGR problem, with the EGR valve disconnected there is no change and the valve when hand tested operates like a new one. The power brake hose is not pinched or obstructed if that is what you mean. I did try to depress the brake pedal to put the engine under some load when it was running and there was no change in operation or unusual change in vacuum.. The engine needed the crank ground and also nad a worn cam lobe, so i replaced the cam with a stock cam, and replaced the lifters, just for more info.

Ok, then I would say that your problem with the engine shutting down is with the Control Module.

Well, I don't know much about the propane systems, but the fuel pressure regulator you would usually change, usually when you have a problem with fuel pressure the diaphram and or the spring go bad and are in need of replacement.


.

I'm embarrassed to say this, but when I crawled under it to change the Knock Sensor, I spotted a spark plug wire that popped off! It runs like new again! Thanks for the help.

I am a diesel mechanic and have been wrenching for 17 years. The machining work and cleaning was done at my diesel shop under my supervision so I am sure it is accurate and everything is clean and in good condition. There was a gap in the intake manifold after manifold was set in place although I used extra sealant on the front and rear of the mating surface. When I realized there was a gap I sealed it by pressing the sealant into the gap and added extra on the outside, but I am thinking if there was a problen here the engine would not produce normal vacuum initially.

Ok, thank you! I changed the part last night and test drove the truck this morning. It seems to be doing much better! And no light. I really appreciate your quick responce, thank you very much!

its alright! we all miss little things like that. glad you found your problem!

check the ignition coil if you can by the way because when a spark plug wire is off and doesnt ground out it feeds back through the coil and can damage it.

i see what you mean. try blocking off PCV to intake.

You are very welcome.

When the PCV is blocked off the idle increases a little but the vacuum problem is still present. I blocked the PCV for a few attempts and got the same results, however when the PCV is disconnected the engine will start better and sometimes did not need the throttle opened to start, and on the first attempt idled on its own at around 300 RPM for almost a minute.

how did you adjust the valves?? i set them at 0 lash and go 1/2 turn so you get better low end. you may have a tight valve if you went the full 1 one turn.

Roy

I set the valves at 0 lash plus 3/4, then re checked them while i had the engine running.

I would back them off 1/2 turn and see if it makes any diference. i have seen issues with new lifters not settling in as they are supposed to.

Roy

I have a 1995 Silverado - 2500 (3/4 ton) 4x4 with a 454 (7.4 liter) engine and I just replaced the (automatic) transmission this spring. Since I've gotten the truck back with the new transmission, it has been running terrible - RPMs all over the place, 'coughing', sometimes backfiring . . . and it dies or stalls almost every time I'm at a stop light or when the wheels stop moving - I need to use two feet (brake & gas) to keep it running at a light.

The 'check engine' light has been on (but it has been since I bough the car [used] a year and a half ago after my previous Silverado was totaled when I was rear-ended by an SUV - but that's another story...) . . . the codes I've checked since trying to diagnose this running problem indicated the EGR valve and MAP sensor - both of which I've replaced - and neither of which has solved the problem. We also checked the coolant temperature sensor - unplugging/bypassing it seemed to solve the running/idling problem - replaced this [relatively inexpensive part], but again, no fix. I've also replaced the fuel filter and ignition module (more recently it's been giving an 'ignition system' code) - neither of which have solved the problem either.

I've tried all of these:

EGR valve
MAP sensor
coolant temperature sensor
fuel filter
ignition module
premium/hi-octane gas

none of them have solved my problem.

What can be wrong with my truck? Might I have been the victim of sabotage? (strangely, not long after the running problem started, each of the four tires needed to be replaced inside of a ten day period - each from seemingly unrelated events - leaks, nail/screw, etc...)

Any insight would be of great value.

THANK YOU.

Is there anyone that may have put something in your fuel tank? Also, have you checked for vacuum leaks? Can you tell me the last codes you found? Have you tried running fuel injector cleaner in the gas? Finally, when you replaced the EGR, was there carbon build up in the intake or the vacuum hose?

Sorry for so many questions. Let me know.

Joe

Hi Joe -

Thanks for your prompt reply to my query - -

I really don't know if someone might've put something in my fuel tank - but I suppose it is possible. I also suppose I'd have to remove the tank and actually look inside it to see if this is the case...? I believe the mechanics helping me (who're both perplexed) checked vacuum pressure - but I don't know if that rules out leaks or not. I will check again and get you the most recent codes - the last codes I know were for the ignition system - which is why we replaced the module. I have not tried fuel injector cleaner in the gas, but I believe my mechanic checked and cleaned the injectors. I replaced the EGR myself and I did not notice any carbon build-up on either the intake or vacuum hose - apart from a very tiny bit of grime (which I scraped off with a razor blade before installing the new gasket and then the new part.)

Thank you for your questions! I hope this info helps clarify some issues - - I'll check the codes again and post the results ASAP.

- PR

Let me know the codes when you get them. It will help. Also, they should be able to get fuel from the schrader valve on the fuel rail. Maybe they can tell if something has been added.

Let me know.

Hello again! I have had some other issues taking unfortunate precedent for a bit (clutch/t.o. bearing and more for my other truck - a Chevy '70' dump truck - and minor repairs/maintenance on a New Holland skidsteer . . . AND, believe it, other trouble with, I think, the starter for this truck now too! Seems to draw down the voltage from ~13V to less than 9V every time I start it - - just this week needed to jump it several times to get going. Test shows the battery to be good. Could this be at all related to my other issues?)

But back to my still persistent running problem(s) . . .

The codes I now get are "36" (Idle Speed Control Actuator - which sounds very likely to me) and "54" (Fuel Pump Relay - sounds likely as well . . . but not as sure how to proceed with checking this one myself though). I also get a "12" code, but I think this just indicates the diagnostic feature is working.

Thank you!

-PR

My 1995 Chevy Z-71 was running fine until I slowed down for a stoplight yesterday when it died. It started back up but continued to run rough and would die if I did not put it in neutral and give it some more gas. When the light turned green, I took off but it was acting like it wasn't getting enough fuel; hesitation, jerking etc. Finally got up to 55-60 mph but when accelerating, it would still hesitate. When I got to the house, it died in the driveway, but started again, running rough. The fuel was less than 1/4 so I thought maybe some trash plugged up the fuel filter. I changed the fuel filter but still have the same results. The spark plug wires all appear to be in good shape and in place.

There is no "Service Engine Soon" light on or any other light on.

Any suggestions?

With no check engine light I would believe it to still be fuel related. Be sure to check fuel pressure, should be around 65 psi if I remember correctly.
I would also reccommed checking the fuel rails, have ran into similar systems and found water/debris in the fuel (usually right) fuel rail, wouldn't hurt to clean them.
Just a couple of ideas, let me know if they help.
Dan

Also, I'm [over]due for a follow-up on my check-up by the transmission place - had that replaced around April-May . . . running problems started the day I got the truck back - but had been sitting for mayvbe six weeks prior to replacing the 4L80E transmission.

Someone else suggested I ask about the 'modulator valve' . . .

Any thoughts on this?

I actually now need to solve my starting problem before I can proceed anywhere with confidence - - the battery seems good, and had a new alternator put in a little over a year ago . . . I'm expecting it needs a new starter - if/unless I can eliminate wiring/connections in the process.

If I can figure out the starting issue , I'll probably be in for the tranny check-up yet this week.

Thanx again!

danauthier,

Thanks for your reply. It turned out to be my fuel pump. I bought this truck brand new and this was the original fuel pump. Not bad for 172,000+ miles.

It has been replaced and now runs fine.

It sounds like you have the same type of luck as I do. As far as the no start, it sounds like the starter is drawing too much power. Your battery should maintain a minimum of 9.6 volts for the ignition system to work properly during start-up. If you can get it to a parts store, they can check how many amps the starter is drawing. That way you can be sure it is the problem.

As far as the other truck, a code 12 indicates no distributor pulse. However, it can also indicate the start and end of the scan. As far as the other items, the idle air control valve will cause an eratic idle and the engine to die at a stop. The fuel pump relay is the cheapest thing to try because I am sure you could find another relay on the truck with the same part number and switch them to see if that helps. If it doesn't, I would say the IAC is the most likely suspect.

Let me know what you find on both vehicles.

Joe

Glad you got it fixed,
Thanks,
Dan

hello -

so sorry to confuse things with info about the other truck - - the starter issue is actually with the Silverado (not the dump truck) . . . anyhow, it was at the store that we confirmed the battery was good, but an issue with the starter - just not sure if I only need to replace the solenoid or the whole starter. Working on this now.

Your description of the idle air control valve (idle speed control actuator?) "...will cause an erratic idle and the engine to die at a stop" describes my symptoms perfectly. Yes, the Fuel Pump relay seems easiest and cheapest - could it be that this sends a signal/power to the IAC? Otherwise it seems like I may need them both...

I'll try the relay 1st - and then - if not solved - the IAC is my [final?!] hope!

I'll post my results.

- PR

okay -

. . . long day . . . replaced my junk starter - one success!

I also removed and 'tested' the IAC - - by checking the ohms on each pair of contact points in the plug receptor - I got a steady 45 (or was it 54?) on each pair (the Haynes manual says the range should be between 40 and 80 ohms). This seems to suggest that the part is working . . . but the problem persists! I also 'checked' the Fuel Pump Relay . . . I don't have a matching relay - - it seems that it should either work or not - - and I never get no gas - just the wrong mix and absolutely errant idling. Oddly, I get gas with as well as without the relay in place?! Shouldn't it kill altogether without the relay - just like a blown fuse? I also noticed the 'feul sol' fuse was missing - I replaced it with a 30 amp fuse - but don't know what this might affect.

A friend may have a matching IAC for me to test against this apparently (but not certainly) working one of mine - if that affects the performance, then I'll know if it's the cause . . .

- PR

If you pulled the relay and are still getting fuel, someone had to rewire something. Like you said, removing the relay should kill the power to the pump. Has anything melted down where the relay attaches?

nothing melted by the relay I can see . . . I did notice that the whole fuse box is under the hood - - in my [Haynes] manual it says that the fuse/relay box should be behind the fire wall in the cab on a '95 model truck - and where it actually is on models '96 and newer . . . ? Why might this be? I believe I have a '95 Silverado.

It could be because when it was produced.

My truck starts/runs fine when cold, when reaching operating temp the service engine soon light comes on intermittently, starts to hesitate and run rough, sometimes stalling.When hot, it's very hard to start, you have to hold the accelerator pedal to the floor, and it blows black smoke, running very rough, until it smooths out some. I obtained codes 15, coolant temp sensor, and code 32, egr, from the ecm. I replaced the following parts- coolant temp sensor, egr valve, egr vacume solinoid, fuel filter, air filter, throttle position sensor. After replacing these parts there has been no improvement, ecm still shows a code 15, but the code 32 is no longer there. Please Help ! Thanks

Have you checked the thermostat operation. IF it is stuck open the a/f ratio will continue to be rich causing runnibility problems like you have.

Does it seem like it takes a while longer than it used to to get good heat?

Engine Performance problem
1998 Chevy Silverado V8 Two Wheel Drive Automatic

I have a 1998 Chevy Silverado that has a running rough issue.I have replaced all 4 oxygen sensors and the feul regulator per the trouble code generated by the PCM.Now when I go to start the engine,2 of the cylinders are filling up with feul and wont allow to it to fire up...Thanks for the help

That sounds like you have 2 fuel injectors stuck open.

Thanks DennyP....I have ordered all new injectors...:)

I am 18 years of age live in cold MN and my 92 Chevy truck is ******* me off. This all started a couple months ago it would start up and idle rough for a couple min of me holding it at 2500 rpms and then would run fine cleared right up, as time went on it slowly got worse as it will not clear out. So now it starts runs rough for maybe 15 seconds and then without doing anything it will smooth out, the check engine light comes on but once I try to give it any gas it chokes out. I cant drive because it has no power and will backfire on me. I have replaced everything from the fuel pump to the egr, tbi, map sensor, temp sensors...etc please please help. I have been working on vehicles for a while and these trucks are nothing new to me....this thing has me flat out stumped.

Great site :-)

hows the fuel pressure? any codes to help?

I have a 1996 chevy 1500 5.7 i have put a new distribitor, timing chain,fuel pump and had a shop put in on a scope. If I let it sit over night and start it it runs great for about 15 mins after that it runs bad. I can shut it off and start it back up and it will only run good for a min or two and then it starts running rough. No one can figure out what is wrong. thank you

Go to this link for further info:
https://www.2carpros.com/articles/engine-misfires-or-runs-rough