Rough Running Engine

If you have the actual error code it would be helpful, but with 350,000? miles, it can be valve springs or other internal engine parts, start with a compression test, wet and dry! post results here...

This guide can help

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

I only did a dry compression test. I can do a wet test if needed, I just didn't have anything handy to get oil into the cylinders.

I pulled out all plugs, stuck a screwdriver in the air intake to hold it open, and pulled the coil wire, then cranked the engine about 5 times and took my readings.

All were between 170-180psi, except cylinder 4 which was 162. I think these readings are acceptable considering the mileage on this truck.

Oddly the plugs from cylinders 5 and 6 were already very black (only in for two weeks) 6 was probably non-functional, as it was just a big glob of tar like substance on it. The engine does not use a lot of oil, and does not smoke.

I cleaned the plugs, checked the gap at .06 and replaced the plugs.

Now the truck won't start at all.

It does not seem to have any spark at all. Perhaps I have finally found my problem or maybe caused a new one. I double checked all the wires, and made sure I hadn't bumped anything while working and didn't see anything. With a screwdriver in the end of a wire, I got no spark at all when turning the motor over.

Is it possible I harmed the coil?

Is there a way to test the coil and/or ignition module with a standard multimeter?

Thanks.

That is a very helpful and thorough, step by step procedure.

I kinda got thrown off on step 5, since the coil connector is not labeled, I assumed the 'pink' wire was 'C' and was chasing my tail until I looked at a wiring schematic. Then I assumed the 'black/wht' wire was 'C' since it was connected to the control module.

Assuming that is correct, I then proceeded down to until I got to step 12, where I did not show the 1-4 VAC, I only showed about .4 VAC on my meter.

I was not sure which connector was the 'VCM C3' connector, or which terminal was the ignition control (IC) circuit as described in steps 15-17, but I did disconnect all plugs from the module, then re-connect.

At this point, I am assuming it is the VCM since I do not seem to be getting hardly any AC control voltage to the Ignition Control Module.

If you have any other ideas, I would appreciate it.

Im having the same problem any fixes?

These trucks had a problem with the injectors. Replace all of the injectors or just the ones over the cylinders with the black spark plugs.

Please let me know if you need anything else to get the problem fixed.

Best, Ken

Hi, I found out that the distributors on the vortecs wear out and cause these problems, some say only 100,000 miles. Mine is 243,000, but a new one fixed it. The OEM are plastic and the shaft starts to wobble as they wear and age and produce misfires.. Got a new one made from aluminum with cap and sensor for $34 on eBay, works great. I first had changed everything from sensors to filters and injectors, but it was the distributor. To set the new one on a vortec you have to use a scan tool, you are really setting the cam sensor since the engine is self timing. Instead I bought an app, Car Gauge Pro and a obd2 blue-tooth adapter I got on eBay (BAFX) and set mine for under $35,

Glad you could get it fixed, that kind of problem can be tough. Please use 2CarPros anytime we are here to help

Cheers, Ken

97 k1500 silverado 5.7 I had to crank the engine over for about 30 seconds until it finally started. after that it starts right up and seems to idle fine and it seems fine when i step on the gas in park. when i took it for a drive it spits and sputters. i changed plugs and wires but still spits and sputters. Please help!!!

what motor?

its a 5.7 vin#R

You could have a fuel pump bleeding down. get a pressure gague on it and turn the key on and then off and then see if the pressure drops very fast?

no CEL on?

97 Silverado 1500, 40,000 miles, 5.7L with auto trans,2wd.......Over the past month the truck has turned itself off (died) 3 times. All 3 times, I dropped it into Neutral and it re-started without a problem. The first time was at a red light, the next time was while going about 20mph, and the last time was while driving about 40mph. I don't notice the truck running rough or any other indications of trouble right before or right after it happens. I'm not real sure what is going on, but am affraid that eventually it won't re-start. Any ideas?

There were problems with the Crank Angle Sensors in those CPI engines. Caused no starts and intermittent stalling

Not familar with a crank angle sensor. What is involved in repair/replacement? Is there a specific brand/type sensor you would recommend?

Should be in the bottom of the timing chain cover. Very easy to replace yourself

Ive had this same problem 4 the last 2 years, i have changed the gas pump, distributor, crank shaft sensor and the problem has not gone away, the computer will not show faults. let me know if you have an answer for this problem and good luck.

mamalonsisimo.....I'm going to start with the crank angle sensor and see what happens. hopefully that will fix the problem. I saw your post and see that you already replaced this along with several other things and you're still having trouble....thats no bueno...

I just rebuilt my chevrolet Chevrolet K-2500 350 5.7L T.B.I. V-8 out of my 1992 K-2500. The engine had locked up so I rebuilt from the bottom up. When I start the engine the idle is rough and only keeps running with assistance. After about thirty seconds the engine will die no mater what
Engine is in initial start up and break in phase of rebuilding.
New piston Rings, main bearings, rod bearings, TPS, oil pressure sending unit, cam bearings, new stock camshaft, lifters, valve seals, professionally cleaned all engine parts, qualified all non replaced engine components, new timing chain.
adjusted rocker arms, checked timing, verified vacuum hoses are in good order and correctly placed. crankshaft was professionally ground and polished to 10/10.

have you done cylinder test to determine misfiring cylinders? i loosen wires at cap, start and lift them off 1 at a time to find cylinder that is not firing properly.

I have not checked, the engine when running is rough at idle, but does not sound like a misfiring cylinder, and that would not explain the loss of vacuum that does not recover, but I will check tomorrow to see if there are firing problems. Thank you and any other suggestions are appreciated.

When I first crank up I have to put I run it for about my foot on the gas and it sputters and runs hard like its missing. After I run it about twenty mins it so it starts idling fine until I turn it off. I try to crank it again right away and runs like trash all over again. Replaced plugs and wires and fuel filter and still didn't help. Please help.

k, i just put an engine in a couple years ago ran fine. about a couple months now. ive been having trouble with it. as it step on the gas it hesitates. when i let up on the gas lopes like i have a race cam and the oil pressure gauge will drop with it not much tho. i thought it was a IAC sensor so i replaced it. but its not that.

Hi: Engine runs rough and misfires when accelerating. Idles fine. Changed fuel filter, plugs, wires, distributor cap and rotor. Thanks George

Hi, thanks for the donation. I'd use a gage and check fuel pressure. Any trouble codes? Your obd1, you should be able to access some mil codes, if there are any? If you up the rpms in park, does it act the same way? Sometimes, a high speed cut-out can be caused by a faulty coil? I can't be sure. I hate to throw parts at anything.

so you did vacuum gauge test and there is a problem?

scan for codes an dcheck for a vacuum leak under tbi unit. spray with choke cleaner rpm will change if it is. also check your vacuum line leading otyour map sensor it sucks together and map can't get any vacuum. check your pcv hose as they get soft and do the same and pcv won't work check fuel pressure for tbi should be 9-11 psi

Have you checked for vacuum leaks? Not only the hoses but the intake too.

Hello, I'm having problems with my 1989 Chevy Silverado 1500. This truck has 112,000 miles and I have kept it well maintained, but it dies while you're driving down the road. It has a propane system that I installed, but the problem occurs while running on gasoline or propane: the "service engine soon" light comes on, the engine starts running rough, like "dieseling", and a few minutes later the truck will die. If you pull over and shut it off until the engine is cool you can get back on the road and it's fine. It only has this problem once in awhile, not all the time, and I have checked and changed every filter, valve, and line I can think of. Computer codes didn't help, and I've been to 3 mechanics. The truck does burn a bit if oil in the exhaust when you fist start it, and the heat gauge reads at 210 degrees when it has trouble, which is a bit higher then normal even with plenty of coolant. Someone suggested to check a exhaust valve, or the distributor/ignition module. Any ideas?

Hello,

What you are describing is pretty instintive of the Ignition Control Module. And with that year it does not throw out any codes or turn on the engine light.


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I will replace the coil tomorrow and let you know the out come. Thanks George

Yes I put the vacuum guage on multiple sources when the engine stalled the first time and the reading is consistent. The engine has good vacuum for about the first twenty seconds or so, although it is fluctuating, and then begins to drop at a rapid rate to zero, where the engine dies. I have tried everything to keep it running but once the vacuum drops there is no saving it even at WOT. This caused me to check and re check the hoses and connections against the schematics, and everything checks out. i pulled the timing cover and re checked the timing which was dead on, and I re adjusted the valves/rocker arms too but the problem persists.

No, i replaced all the hoses. But havent checked the intake. Ive seen an easy way to check for vac leaks but cant remember Do you know of any?

The codes that came up where all wrong, so that makes sense. But the light does come on. Could that still be it? Is it a "simple" fix? How much am I looking at to replace it? And is it something I can do myself?
Thanks for replying!

Thank you for using 2CarPros.com. We appreciate your donation and look forward to helping you in the future.

EGR problem?

many people will use carb cleaner and spray it around the intake. If the engine speed picks up, there is a leak. Just be careful that you don't cause a fire.

You would be looking at $80 - $100 for the part. It is mounted inside the distributor but you should be able to do the job yourself.

Before you do anything, what were the codes you got?

Depending on the codes and defs they could indicate another problem or lead me to something esle.


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pinch off brake vacuum?