Engine has a lack of power?

Do you have any codes? have you ran a exhaust back pressure test yet? Check out these guides to help us find the problem.

https://www.2carpros.com/articles/engine-has-low-power-output

and

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Please run down these guides and report back.

Exhaust pressure is fine , no trooble codes at ell , just very sluggish acceleration , I think its either a clogged fuel filter , or a ignition problem , wires , coils , cap and rotor , I put lucas octane booster in it and it has just has a synthetic 10w30 oild change the truck has 400K on it and she's still going strong this has just recently started where she has become extremely sulggish and is lacking power

The truck aslo has a Cold Air intake on it plus a few other performance mods , I'm not really an amateur when it comes to cars I have been working on them since I was 7 years old , I'm going to replace the plugs and wires see if that's the problem as I was going to be purchacing MSD complete igniton for it anyways , also I'm going to replace the EGR valve and fuel filter as I haven't replaced those in about 3 years , it could also possibly be an bad o2 sensor as well it looks to me like I might have a bunch of replacing of small parts to get done , oh well an afternoon with some beer and music it'll get done!

Ignition problems wouldnt cause a lack of power they cause missing.As far as the fuel filter goes you see if its restricted by removing it and blowing thru it not with a air compressor it should flow freely.So have you gotten any where replacingall those parts?

Engine Performance problem
1999 GMC Sierra V8 Four Wheel Drive Automatic

Hi,

My 1999 GMC 2500 has the 6.0 liter vortec engine with an automatic transmission with tow options and 71K miles.

I am am and have been experiencing problems that occur only while towing otherwise the vehicle runs flawlessly.

While towing, I tow a fifth camper, the engine looses power and is unable to tow. Looses power meaning that with 'tow haul' disabled or enabled am only able to crawl along at 20 miles and or so with fuel pedal fully depressed.

This is what has been replaced at the GMC dealership already:
replacement of fuel pump, fuel filter, exhaust manifolds 2eac, and complete new exhaust system too include replacing two costly catalytic converters. Two sensors were replaced and the truck still has the problem.

Needless to say I am discourgaged to deal anymore with the local GMC dealership as I just paid over 5K for the above work to be performed that did not correct the problem. Is there anyone that possibly shed some light on where the problem may lay so I can take it a local mechanic?

Again without the trailer attached there are no issues whatso ever with the vehice, transmission or engine.

Thanks in advance!

Tony

my little bro had a similar problem he discovered that two of his injectors were partially clogged causing a slight misfire under a load and the computer whet into safe mode and would only let him get to about 25 or 30 mph. he removed the injectors and cleaned them and no problems since.

Hi,

Thanks for the reply - it makes sense that if the fuel injectors were fouling out under load it would cause issues with the exhaust, hence the computer code which prompted the expensive repairs which did not cure the issue.

My next question is how to does one determine
if the fuel injectors are potentially fouling under load? Would this throw a computer code?

Thanks again!

yes and no sometimes it will throw a code but since it only does it when your haulin it may not throw a misfire code. the only way we found that the injectors were fouling was to take them out one at a time and look at the bottom and you may see some junk in them and just take some carb cleaner and spray them. there actually really easy to get out it took us about 45 min to do all 8. now this may not be your problem but its cheap and easy and worth a try. good luck

I'll be driving around 70mph on the freeway and the speedometer will start rapidly fluctuating. I'll slow down to around 60mph and it still continues. After a while, it feels like the engine loses power and it drops to around 45mph. I'll try to hit the gas more, but it just sounds like the engine is revving. I'll pull over to the side of the road and wait a bit to drive again. I started driving again but kept it under 55mph, and it'd be fine. If I went up to 57mph, it would act up again. I had this problem last winter, and we realized it was because I had the 4 wheel drive on while driving long distances. After we discovered that, I hadn't touched the 4 wheel drive since. However yesterday, 8 months or so later, I had the same problem. I made sure that it was in 2 wheel drive, so I have no idea what else it could be.

scan for codes and check fuel pressure with a gauge first

We scanned the codes and did a diagnostic last spring and they were fine. It showed no problems, though it was not acting up at the time. The check engine light never came on. The fuel pressure isn't the issue, because I was able to continue at the same speed while the speedometer was acting up. In brief, the speedometer fluctuates down and back up again, at first from 50-60, eventually getting worse and going down 30-60. The truck in spurts acts like its in neutral and the engine will rev up when accelerated, but the truck itself slows down to 45mph. If I keep trying to drive, it'll stay around 45mph, but I usually pull over because it doesn't feel safe to drive. After 5-10 minutes rest, often with the engine still running, I'll drive again, and it'll be fine for a bit. The tranny fluid is good, as are the other fluids.

you need to scan for codes now not last spring and you need to check fuel pressure first cause it can be low but still operate then check vacuum at idle.

Engine Performance problem
1998 GMC Sierra 350 Vortech Four Wheel Drive Automatic 192000 miles

When I crank up everything is fine. When I put the truck in gear my speedometer and tacometer and odometer don't work and when I take off it is really sluggish and acts like it doesn't want to take the gas. I have been told it was and oxygen sensor, or octane sensor...not sure which is which or if there is such a thing.

check the engine for codes to see if it's what you think it is. it could be broken fuel lines inside the intake manifold. but it all has to be checked first.

I recently replaced the Idle air control valve, throttle postion sensor,MAFS, O2 Sensors, thermastat and for some reason it keep cutting out on me. What else can I check since I am a novice mechanic. Im not getting any codes and it seems difficult to start which takes about 3 times and with a little help from me pressing on the gas pedal

Check and test the coolant temperature sensor and EGR and PCV valves if okay test the fuel pressure and comeback with the readings we start here

Called the mechanic that worked on it the other and said the vaccum were within range. He also suggested the temperature sensor I'm waiting for it to cool so I can pull out to check it. PCV valve is also brand new I forgot to mention last night. Dumb question how would the temperature sensor affect the truck? The mechanic said the sensor may not relaying back to the computer that it is operatoring at 190 degrees since I could had the wrong thermostat install which was giving them a reading of 160. I hooked up my program to the truck and I was getting a reading of 194 degrees. Wouldn't the sensor register as bad at this point? Thanks for the help sorry I'm asking a lot of questions just tired of it quitting on me it good truck and plan on keeping it for a few more years. Thanks
Gilbert

Check the fuel pressure to rule out a clogged fuel filter and fuel pump

changed out fuel filter havent been able to fuel pressure reading. The shop said it was good when I talked to them yesterday. But i have a new problem when i taking the temperature sensor I saw that the I think it the upper intake manifold was cracked where the temperature threads into. Is that the right name "upper intake manifold"; i filled it in with soem RTV I dont see any leaks and made sure to put teflon tape on it and was as careful as one could be when installing the temperature sensor to avoid cracking it anymore. Doesnt seem to be holding back anymore but the start is still a little sluggish

truck is hard to start. chugs really bad when idling, almost like a lope. has a hard time accelerating from a stop, and sometimes will stall or bog really bad. uses alot of gas for a v6. smokes sometimes when started and reeks of a gas smell. i have a p300 multiple cylinder misfire code. ive replaced the cap, rotor, plugs, wires, coil, and fuel filter.

Hello_

The random misfire DTC indicates multiple cylinders are
misfiring or the PCM cannot identify which cylinder is misfiring.
The underlying cause is often a lean fuel condition, which may be due to a vacuum leak
in the intake manifold or unmetered air getting past the airflow sensor.
Check also for a malfunctioning Camshaft position sensor (CMP) or stuck open EGR valve.

Hi guys, first time I've ever tried coming online to ask someone because I'm completely stumped.

Disclaimer: I am not a mechanic, have just figured it out by ear my whole life.

My vehicle: 1996 GMC Sierra 1500 2WD Auto w/ 5.7l Vortec

Beginning: Just bought the truck for next to nothing with bad engine. Replaced engine 1 month ago with identical engine with "140,000" miles on it. (Who really knows right... it looked and ran great for last month.) My buddy and I split the work and turned it into a few hour process. In doing so, we somehow managed to completely miss plugging the map sensor back in this whole month.

Middle: The truck ran strong, minus a very quick and sudden complete stall, if you stepped your foot in the gas. The stall actually felt like the truck just "shut off" for about 1 second, then vroom. The truck also smelled like it was burning lean, but I never had time to tinker with it.

About 2 weeks ago, I started to notice that the truck would run kind of rough and vibrate/shake any time you were "coasting" down the road and barely had to touch the gas petal to remain at 30 mph/45 mph/55 mph for city speed limits. It also felt like the truck would shift too early and sort of bog down.

Today, I drove the truck for about 10 miles and on the way home, I noticed that the truck would do that "pipe pop" like a manual transmission when you rack up the rpm's and let off the gas. (I have dual exhaust from manifolds to 2 flow master mufflers and echo tips, no cats). Anyway, normally, if I was going 45mph in 3rd gear, and let off the gas, it would seem like it went into "neutral" and quietened down. Today, it was doing the "pop pop pop BOOM pop pop" sound. It actually backfired a few times. When I noticed it do it by itself, I got curious and actually put it into 2nd manually, to see if it would do it again. It did. I NEVER abused it and the RPM's never went over 2.5k in the process... I think it red lines at 6 or 7...

After I got it home, didn't think anything about it, because it was cold this morning, cold start, left quick..

Ending: Later, I took the truck again, but made it about 8 miles before I just lost all power. I was on the interstate, attempting to reach 75 mph and keep up with traffic when it just progressively lost power. By the time 5 more miles were up, I was on the interstate going 50 mph with my foot almost in the floor. So I let off the gas and putted to the nearest exit, where I parked it at an autozone.

I had autozone do a diagnostic scan, and it said MAF and MAP sensor. (This is how I found out the map sensor had never been plugged back in)

The truck would start, idle poorly, then eventually adjust up to being able to idle fairly... but the moment I put it in gear, it just bogs down and loses all power.

I have another vehicle (98 z71 w/ same motor) so I changed the MAP sensor, the MAF sensor, the idle air sensor and throttle position sensor with the other vehicle and no difference other than idling more poorly with different configurations of swapping parts. (I did not do battery reset between sensor testing). I tried changing the entire breather and no difference. I had recently replaced the fuel sending unit and the guys that did my exhaust removed my cats and wouldn't let me keep them......

I have not tried crank sensor, cam position sensor or anti-knock sensor.

Tonight after dark, I went back out to the truck to tinker and noticed that I got a neat little display show from 4 plug wires and my coil wire going to distributor. The second and last plugs (from front) on both sides, were jumping. Not a strong jump, just enough to show a fuzzy blue light show. The connection at the coil was doing the same thing. So #4, #8, #3, #7 and coil. Everything was closed, so I couldn't change plugs and wires yet.

So right now, my truck idles at almost correct state, but vibrates. The moment I attempt to put it in gear, it bogs way down and tries to die, and shakes horribly. If I try to drive, I have no power. With petal 1/2 way down, I would hit 30 mph in about 4 minutes...

Could it just be the plugs/wires? Is it something more simple? Until I noticed the sparks, I was going to try fuel filter next. Or thinking I got water-gas...

Any ideas on what to try next?

It sounds like you have two problems the first is the popping from the exhaust this would be your air deverter valve stuck open or the diaphragm is blown. This is a common problem I would replace both. Here is a guide to show you how:

https://www.2carpros.com/articles/engine-backfires-while-running

I would also replace the plugs and wires with AC Delco Parts.

Please let us know what happens.

Cheers,

To clarify, the popping sound is coming from the exhaust, just to demonstrate the similar behavior to a manual transmission vehicle's sound when you leave it in 1st gear, hit 4,000 RPM's and then let off the gas. How it slowly goes back down RPM's and goes "pop pop pop pop" as it's doing it.

There is no popping sound coming from the intake/engine at all, except the typical clinks of an engine that's just about ready to die. (The sound all movies make when a car breaks down while still rolling) and that only happens when I put it in gear.

Replaced spark plugs/wires and tested each for adequate spark and found something strange. We were able to remove all spark plug wires from the passenger side and there was no difference in how the engine ran. So #2-#8 cylinders are not working. Where would I even begin?

It sounds like you have lost the spider injector under the upper intake manifold. Here it is on Amazon for $180.00:

https://www.amazon.com/gp/product/B01NAAGMV2/ref=as_li_qf_sp_asin_il_tl?ie=UTF8&tag=2carprcom-20&camp=1789&creative=9325&linkCode=as2&creativeASIN=B01NAAGMV2&linkId=3ab81783c478d71409cc7c3e11248acf

Here is how you change it (below)

Please let us know

Nice you are right on the money, I did both deverters and changed the injector and it worked great thanks for your help. This site rocks!

Nice work, we are here to help, please use 2CarPros anytime.

Cheers, Ken

Engine Mechanical problem
1990 GMC Sierra V8 Four Wheel Drive Manual

What would be the reason that an engine idles great and then falls on its face when you accelerate?

alot of things cause this, a blown gasket between the TBI unit and manifold, low fuel pressure, paritally plugged fuel filter plus many other things. Run a scan on the engine for codes and change teh fuel filter. see if that helps..