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1990 Chevrolet C1500 won't start when cold
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paulg
User
Dec 13, 2016, 2:01 PM
Post #26 of 41
(1067 views)
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Re: 1990 Chevrolet C1500 won't start when cold
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One of the car guys here at work suggested the ECM was bad - any thoughts on this? While they aren't stupidly expensive I'd rather not just blindly keep throwing parts at it, so any suggestions as to a test approach?
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Hammer Time
Ultimate Carjunky
/ Moderator
Dec 13, 2016, 2:16 PM
Post #27 of 41
(1064 views)
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Re: 1990 Chevrolet C1500 won't start when cold
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You need to first identify what is specifically happening before you start concluding what the cause may be. You have nothing to point to a computer issue yet.
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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.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Dec 13, 2016, 2:35 PM
Post #28 of 41
(1058 views)
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Re: 1990 Chevrolet C1500 won't start when cold
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Sorry if already covered or ruled out but by age has valve timing been ruled out? Yes it's a chain not a rubber belt but likely to have a nylon cam gear still OE and could be nice even worn teeth or have jumped such that compression isn't enough and it would fool vacuum measuring controls.
If not tested without a novel just see what a couple cylinders are for compression and an actual intake manifold vacuum reading at idle however you can get it to run.
Just age it should be ruled out and no you can look right at it just do those checks as since so much adds up and it isn't right this would fool a lot of testing,
T
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paulg
User
Dec 13, 2016, 2:35 PM
Post #29 of 41
(1058 views)
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Re: 1990 Chevrolet C1500 won't start when cold
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Well, it's not strictly true that there's nothing pointing at the ECM - by a process of elimination, there's really not much else it can be.
I've proved out the fuel system from pump to injectors, and I'm confident the ignition system is working. That leaves....the ECM, the battery and .....well, not much else. Unless you can think of something that is....
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Hammer Time
Ultimate Carjunky
/ Moderator
Dec 13, 2016, 2:40 PM
Post #30 of 41
(1054 views)
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Re: 1990 Chevrolet C1500 won't start when cold
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That couldn't be further from the truth.
The ONLY thing you have truly eliminated is fuel pressure. The tests you have performed are far from conclusive.
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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.
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Hammer Time
Ultimate Carjunky
/ Moderator
Dec 14, 2016, 7:48 AM
Post #33 of 41
(1027 views)
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Re: 1990 Chevrolet C1500 won't start when cold
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Although many of your DIY methods will suffice in most cases, they are no substitution for the correct diagnostic equipment and years of experience to make keen observations that may spot a cause.
To date you have not identified what is actually taking place to cause the lean mixture and therefore are not even close to condemning an ECM. I think you would do better to spend your money on a highly skilled diagnostic tech rather than continuing to throw parts at the problem.
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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.
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Hammer Time
Ultimate Carjunky
/ Moderator
Dec 14, 2016, 7:59 AM
Post #35 of 41
(1019 views)
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Re: 1990 Chevrolet C1500 won't start when cold
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I don't know where you are getting those numbers from. Most shops diagnostic charges are 1 to 2 hours, usually 1.
You never know, they may isolate the cause in a matter of minutes. That's where experience comes in.
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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.
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Hammer Time
Ultimate Carjunky
/ Moderator
Dec 14, 2016, 8:21 AM
Post #36 of 41
(1009 views)
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Re: 1990 Chevrolet C1500 won't start when cold
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Also, I can't stress enough that you find the right shop. DO NOT just go with the cheapest. DO NOT go to any of the chain locations or tire stores. Find a shop with a reputation for quality.
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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.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Dec 14, 2016, 8:22 AM
Post #37 of 41
(1007 views)
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Re: 1990 Chevrolet C1500 won't start when cold
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1st I agree a professional diagnosis would now save a lot of time and no doubt money.
Quote ">Sorry - I'm struggling to follow what you're saying here. I *think* you're saying I should check cam timing - how? Even if the cam chain has jumped a tooth, the compression wouldn't be affected, so I'm not sure what the compression test would show.
I've never done a vacuum test - what should it be? I'm assuming I pull off one of the vacuum lines and just measure the pressure, right?
For the record, the truck is relatively low mileage - 98000 or thereabouts.<"
It's a NYLON cam gear. They like plastics do get brittle, wear faster than metals. You can tell if actual intake vacuum while at a steady idle is off. Average to expect is around 18Hg = inches of mercury. So much is reading that info to decide what to do for fuel delivery by other sensors it matters. Compression would be evenly lower than expected. Low intake vacuum suggest to sensors that it's under load or can't adjust properly at all. Once running it apparently deals with it enough to run and can up to a few teeth jumped off then engine can't run anymore at all low miles or not for any reason it's off the mark by more that about 7 degrees of timing as seen by crank damper motion vs distributor rotor if checked engine off turning engine both directions how far crank can turn before distributor rotor turns as well.
That's all is rule it in or out. BTW - for ages if/when a regular person's vehicle in my hands happened to need a water pump for example at about 4-5 years old and 100K area would ask if vehicle was expected to go on for lots longer go one extra step and do that and be done with it for the life of the vehicle. All but one of countless was already worn and had cracks in that nylon gear that early never mind this age. Thing is plastic so doesn't tolerate being cold then hot over and over again.
In fairness ones already failed partly would near always jump and be off then jump back and run properly for a while before it alone was the problem.
Now just asking to rule it in or out is all,
T
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paulg
User
Jan 27, 2017, 2:37 PM
Post #39 of 41
(973 views)
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Re: 1990 Chevrolet C1500 won't start when cold
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So resurrecting this necro-thread to post what the problem turned out to be.
The throttle position sensor had failed such that it never went below 2.5v - at rest, it should have been 0.45v or thereabouts. Once it got above 2.5v it was OK, but that put the ECM in the "clearing flood" mode, so it leaned everything out.
Guess I've got a nice clean fuel system now.....
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Hammer Time
Ultimate Carjunky
/ Moderator
Jan 27, 2017, 4:51 PM
Post #40 of 41
(964 views)
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Re: 1990 Chevrolet C1500 won't start when cold
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That makes sense. Kinda surprised it didn't set a code though.
That didn't do anything for cleaning your system though. All it did was make the engine run rich at low throttle and possibly too lean at heavier throttle. Neither are good for the engine.
I will close this thread now as solved.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 28, 2017, 12:07 AM
Post #41 of 41
(957 views)
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Re: 1990 Chevrolet C1500 won't start when cold
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Should have easily set a code or been found with as little as an incandescent test light watching it dim but didn't.
It's NOT nice and clean now rather the opposite as HT just said not good for it. I would give this a decent highway run meaning work it some will help to burn off junk or perhaps make something show up but worth knowing if truck is worth it at all it's an asset as a real truck if nothing else.
If you wish to comment as this is page two just refer to this thread and start a new one where you stand with more current info is probably best,
T
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