Question about 1990 GMC K2500

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1996 GMC k2500 7.4L... Engine test passed, but still has problem

Hello!
I greatly appreciate your website and your willing to help! Here is my story about my truck: For a long while, my truck runs okay, but once or twice in a driving time, two of the pistons got no gas or no electricity to fire up. I changed fuel filter, spark plugs, firing wires, dispenser cap/rotor and also, I added a new battery. After all of these replaced, my truck still runs roughly.
So, I gave up trying to fix it. Yesterday, I took it to GM dealership for the testing. For all day yesterday and this morning, the GoodWrench team are still strugglied to find an answer to this problem. This morning, a tech called me and said that they had no luck finding any problems with their advanced test system.
As of now, I haven't gone to their shop for the list of tests they did so far, but I knew that this problem is so unusual and uncommon for any tests to find. They told me that they did many various tests in according to their educated test preformance.
Now, I am despairate to find someone who can anayzle this problem with his/her logistic thinking. Now, do you think that you can help me with different ideas of finding a problem?

Thank you very much for your help!

Please don't hestiate to ask me further questions, I really need some ideas!

Todd

Posted by on

  • tcorbett Jan 28, 2009

    I meant They had no luck find any problems with my truck even though they were using their advanced test system. This sentence replaced that last sentence of a second paragraph. Sorry for this misunderstanding.

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First i have to assume that the tech at GM have checked fuel delivery and ignition secondary(plugs,wires ,cap and rotors and coil) . so we have good fuel pressure, clean fuel filter and good injector.secondly the engine compression and mechanical is fine.
for engine to run smooth we need 6 element
1 compression
2 fuel
3 spark
4 air
5 timing
6 unrestricted exhust
any interuption in quality and quantity of this element will cause the engine to rrun rough or not at all.
i had a 1995 GMC with the similar problem in my shop few months ago .finally i found that it was a ECM (computer) ground wire (was located at intake manifold was bad and caused the primary ignition to act up. check with GM and make sure it is not an ECM issue which sounds like it .let me know and inform me what kind of test they did with result so i will be able to help you more.i hope i shed some light on your delama.

Posted on Jan 28, 2009

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Re:"two of the pistons got no gas or no electricity to fire up"

You need to find out if there is spark.

To find out you use a tool like this:Inline Auto Ignition Spark Plug ...

If there is no spark then it is a distribution problem.


If there is spark the mechanic must test fuel pressure/volume with a Compression Tester

If fuel pressure is fine, they need to check timing.

If fuel pressure is below normal, they need to test fuel pump, lines, do an injector cleaning.

What have been done at the garage is just a superficial ECU (car computer) scan. Take car back and complain, a mechanic should be able at least to address the reason for the problem, probably they need to spend some more time on the car.

Posted on Feb 09, 2009

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Hi and welcome to FixYa,

Your described issue would seem to be an intermittent electrical connection, loose. A couple of ideas you may want to consider:

  • start the truck in a darkened area/night. Have somebody throttle it up varying the RPM. With an insulated rod, move/wiggle the sparkplug wires. If there is any spark arcing, it would be visible and that could cause occasional misfire;
  • locate the truck's engine computer. Check, clean and/or tighten the connectors. In some cases it may be necessary to scrape them to expose fresh metal;
  • locate the injectors of the erring cylinders. Similarly as above, check, clean and/or tighten the electrical connectors. In some cases it may be necessary to scrape them to expose fresh metal.
Interesting that there were no error codes when scanned. Would appreciate any updates on developments.

Good luck and thank you for using FixYa.



Posted on Feb 08, 2009

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Welcome to Fixya! Your Solution, As Short and Sweet as it Sounds, Is to Replace the ECU Box on this Truck. I have dealt with this Problem Before and repaired the Same Items before replacing the Computer as the Last line in Defense. This will fix your Problem. Please Rate My Response! Thanks!

Posted on Feb 08, 2009

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I would say just to give it a shot, check your EGR valve, and your sensor, I dont know if this will work just recomendation

Posted on Feb 08, 2009

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Here is where I would start, first off this can be a bad COMPUTER on this vehicle. I would have that check first off. I would also check The crank sensor because that control the spark and all so the cam gear that this sensor reads from (mounted on Crankshaft). If it has broken teeth it will not provide spark to all cylinder through reference signal to coils. Second I will check camshaft gear and sensor because they provide the reference signal for injector to pulse, same here if there is a broken teeth you will not get signal to certain injector, therefore NO gas to cylinders. If any of these problems are intermittent they will NOT show up on a diagnostic machine. My personal opinion by just listening to what you said I would think COMPUTER is bad. Good luck and thanks for using FIX YA

Posted on Jan 28, 2009

  • O Mclean Jan 28, 2009

    I MEANT CRANK GEAR THAT THE CRANK SENSOR READS OFF OF...

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This sounds like the ICM maybe overheating,You can try replacing the heat grease under it and see if that helps,If not,just replace it.

Posted on Jan 28, 2009

  • Randy Hough
    Randy Hough Jan 28, 2009

    The heat grease under it statement ,Only applies if it is located inside the distributor

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Hi!

I think the piston coupling has worn out or become loose, do check for that.

Please revert for any clarifications

Thanks
Rylee

Posted on Jan 28, 2009

  • Rylee Smith
    Rylee Smith Jan 28, 2009

    Also check the ECM (Electronic Control Module) which is located beneath the steering wheel inside dash board

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Hello there if it passed the engine test try cleaning the throttle body this can sometimes cause rough runnig and irrtic idle, also check induction pipe(the pipe that goes from carb to airfilter for splits .
you could have a friend blip the throttle while you cup the pipe and work your way down if you feel suction on your hand then you have a split pipe just a thought thanks for using fixya!

Posted on Jan 28, 2009

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WHERE I LIVE SOME OF OUR AUTO PARTS STORES LIKE CHECKER, PEPBOYS, FIRESTONE, AUTOZONE WILL COME OUT TEST YOUR CAR WITH A CODE MACHINE AND SHOW YOU WHAT THE CODE MEANS

NOT ALL DO THAT, HABOR FRIEGHT TOOLS SELLS THAT DEVICE AND YOU CARRY IT IN YOUR CLOVE BOX ITS 89.OO AND UP BUT NOT MORE THAN 100.00 DOLLARS

ROD

Posted on Jan 28, 2009

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When Was The Last Time You Had A Full Tune Up?
How Many Miles Are On The Engine?
Did They Check The Timing?

Posted on Jan 28, 2009

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Sounds like a vacuum situation maybe.I would try checking the fuel lines and assembly as well. your fuel pump could be malfunctioning also. Check to see if your dispenser cap is in the correct position too. oh, one more thing, the points are vital. make sure the points are installed correctly.

Posted on Jan 28, 2009

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