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90 GMC 1500 poor start misses out


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Hillbilly910
User

Aug 11, 2011, 8:12 PM

Post #1 of 15 (2328 views)
90 GMC 1500 poor start misses out Sign In

has a 350 TBI, high milage(over 300,000) burns some oil and fouls some plugs...now you know
truck was running great all things considered, started missing out at high-end speeds in O-drive, and slowly got worse. Now it wont start in the morning unless you hold the gas pedal to the floor, starts extremely rough, but once started runs ok for 8-10 miles, then slowly starts to miss out worse and worse. The gas is not the problem(tired differnet places)

Changed distributor cap,rotor button and wires 6 months ago, just changed all plugs a week ago. No engine lights come on. Changed fuel filter 6 months ago as well.

Gas milage has went downhill leading up to this.

Any ideas?


Hillbilly910
User

Aug 11, 2011, 8:15 PM

Post #2 of 15 (2326 views)
Re: 90 GMC 1500 poor start misses out Sign In

also, are there ignition codes for this truck? I had a 92 where you could turn the key on and off like 3 times and certian lights in the dash would flash indicating where a potentail problem was.

HB


Sidom
Veteran / Moderator
Sidom profile image

Aug 11, 2011, 8:23 PM

Post #3 of 15 (2325 views)
Re: 90 GMC 1500 poor start misses out Sign In

Well considering the mileage.....You should probably run a compression test & post the results, do & wet & dry test. Also for this problem we would need a fuel pressure reading, I know it's not easy on this model but to move forward we need to know what the reading is.....Also, if you can get the codes pulled.......


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Aug 12, 2011, 3:08 AM

Post #4 of 15 (2294 views)
Re: 90 GMC 1500 poor start misses out Sign In

To extract a trouble from the computer for diagnostic purposes, the Assembly Line Communication Link (ALDL) connector is used.
Ground terminals A and B with the ignition "ON" and engine not running. The system will enter the diagnostic mode. In this mode, the computer will display a 12, three consecutive times, by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" or light. A 12 consists of one flash, a short pause, then two flashes in rapid succession.
After 12 is displayed, any stored trouble s will be displayed by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" light. All s are displayed 3 times each then a 12 will repeat. In the diagnostic mode, the computer will also energize all computer controlled relays and solenoids.


ALDL Connector (Located Underdash)


The ALDL diagnostic connector is located in the passenger compartment.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Hillbilly910
User

Aug 15, 2011, 2:56 AM

Post #5 of 15 (2277 views)
Re: 90 GMC 1500 poor start misses out Sign In

UPDATE
truck sit for 2 days, went last night to take it to mechanic for recommend tests, truck wont start, never offers to fire. The fuel pump is making normal noise.
There is no fuel spray coming out of the injectors, regardless throttle input.
In a last ditch effort, i poured some gas down into the TB, absolutely no fire...

idea's?


Hammer Time
Ultimate Carjunky / Moderator
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Aug 15, 2011, 3:02 AM

Post #6 of 15 (2274 views)
Re: 90 GMC 1500 poor start misses out Sign In

   All "crank, no start" conditions are approached in the same way. Every engine requires certain functions to be able to run. Some of these functions rely on specific components to work and some components are part of more than one function so it is important to see the whole picture to be able to conclude anything about what may have failed. Also, these functions can ONLY be tested during the failure. Any other time and they will simply test good because the problem isn't present at the moment.
If you approach this in any other way, you are merely guessing and that only serves to replace unnecessary parts and wastes money.



Every engine requires spark, fuel and compression to run. That's what we have to look for.

These are the basics that need to be tested and will give us the info required to isolate a cause.

1) Test for spark at the plug end of the wire using a spark tester. If none found, check for power supply on the + terminal of the coil with the key on.


2) Test for injector pulse using a small bulb called a noid light. If none found, check for power supply at one side of the injector with the key on.


3) Use a fuel pressure gauge to test for correct fuel pressure, also noticing if the pressure holds when key is shut off.

4) If all of these things check good, then you would need to do a complete compression test.

Once you have determined which of these functions has dropped out,
you will know which system is having the problem.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Hillbilly910
User

Aug 15, 2011, 8:33 AM

Post #7 of 15 (2267 views)
Re: 90 GMC 1500 poor start misses out Sign In

no spark at the plugs, gonna check coil in a few mintues, will try checking the injector for power, but not exactly certain on that, but will try.

Thanks for all the help, will keep relaying info as i find it.

HB


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Aug 15, 2011, 9:56 AM

Post #8 of 15 (2262 views)
Re: 90 GMC 1500 poor start misses out Sign In

It's not just power that you have to check at the injector.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Hillbilly910
User

Aug 15, 2011, 10:34 AM

Post #9 of 15 (2258 views)
Re: 90 GMC 1500 poor start misses out Sign In

OK
Not exactly sure how to test the coil, more wires than im used to...got a grey plug and a black plug, each have a white and red wire, so what do i do to test it? i have a continuity tester and a multi-meter.

Also, did the paper clip thing in the under dash link, it just kept flashing 12's(one flash,pause,2 flashes and long pause) over and over. Am i mis-interpreting the flashes, or is it not recognising a problem.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Aug 15, 2011, 11:47 AM

Post #10 of 15 (2256 views)
Re: 90 GMC 1500 poor start misses out Sign In

OK, if you're not going to follow instructions, then you're on your own.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Hillbilly910
User

Aug 15, 2011, 12:46 PM

Post #11 of 15 (2252 views)
Re: 90 GMC 1500 poor start misses out Sign In

sorry, guess i missed something, i checked for spark at plugs, none
not sure how to check at the coil, thats all i was asking
thought i was follwing instructions


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Aug 15, 2011, 12:58 PM

Post #12 of 15 (2249 views)
Re: 90 GMC 1500 poor start misses out Sign In

I though you were trying to check the coil itself. You just need to verify power into the coil with the key on.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Hillbilly910
User

Aug 15, 2011, 4:48 PM

Post #13 of 15 (2244 views)
Re: 90 GMC 1500 poor start misses out Sign In

Replaced the ICM(after testing for power at coil, at recommendation of several mechanic) it was bad, i now have fuel and spark at the plugs, truck is still crank no fire...
guess im down to compression testing now. Still odd i have absolutely no fire at all, no hint of combustion.

HB


Hillbilly910
User

Aug 17, 2011, 6:54 PM

Post #14 of 15 (2230 views)
Re: 90 GMC 1500 poor start misses out Sign In

truck is repaired
the ICM was the problem, after installing it, i had neglected to get the rotor seated correctly, and it fried, giving me intermitent spark at the plugs.
Replaced rotor, truck runs like a champ

Thanks again for the help!

HB


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Aug 18, 2011, 4:48 AM

Post #15 of 15 (2224 views)
Re: 90 GMC 1500 poor start misses out Sign In

Thanks for the report of the fix,

T







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