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1990 Chevrolet C1500 won't start when cold


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paulg
User

Dec 1, 2016, 8:41 PM

Post #1 of 41 (457 views)
  post locked   1990 Chevrolet C1500 won't start when cold  

OK folks, let's get some brain power here :)

So the symptom is that when it's cold, my 100k mile 1990 C1500 will not fire - cranks and cranks but no go. However, a splash of gas down the throttle body and away we go. Once started, it runs fine, a little down on power but drives and idles fine.

If the engine is hot, it fires right up, no problem.

So I figure - must be fuel, right? So I change the fuel pump. Twice. It currently has a nice quiet Delco one. No change.

So I change the fuel filter (silly me, missed it the first time) and the fuel pressure regulator. Still no change. Cranks but doesn't fire up unless you add gas to the throttle body.

So now I'm desperate. There's not much else it could be, right? So I change the fuel injectors. At this point I've changed everything except the fuel pipes. No change. Still the same.

So I sit down and think - maybe it's being TOLD by the sensors to do crappy stuff - so I change the coolant sensor. No deal. And because I have one around I also change the rotor arm and distributor cap. No dice. Just as before.

Finally, in an act of desperation I thought - it sounds like it might be ignition timing related - so I changed the ignition module. No deal. Still the same.

So. I'm stumped. I've worked on cars a LOT over the last 30 years or so, but this one has me beat.

Help me please.......


paulg
User

Dec 1, 2016, 8:44 PM

Post #2 of 41 (453 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

Oh, one more thing - it has ODB1 which is less use than a rubber screwdriver, but what the hell - I figure it might help so I pull the codes.

Nope. No code stuck in there, and in fact the only issue I've had over the last 3 years or so was the EGR valve got stuck, so I disconnected the valve so that it idled OK.


Tom Greenleaf
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Dec 1, 2016, 9:28 PM

Post #3 of 41 (442 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

"Less use than a rubber screwdriver" - Crack me up!Sly


It can help and should at least communicate or will screw you up. EGR unplugged? Why not fix the thing as it's probably leaking at idle causing the problem and code really should show. Clean it first - pintle under side should hold carb cleaner IMO and it shouldn't have vacuum to diaphragm while at idle or it's messed up.


Once again, bulb check the CEL works with just key to run, engine off it should stay lit. If not see if it's missing or blown. A lot of people get sick of getting a sunburn from them staying on and go nuts to make it go out but taking it out isn't the answer and can be the problem itself. No bulb, no codes even if useless up to erratic operation,


T



Hammer Time
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Dec 2, 2016, 5:07 AM

Post #4 of 41 (436 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

Maybe it's time to stop simply throwing parts at it and do some actual testing.

What is the fuel pressure.
I assume this is a TBI system. Can you see fuel coming from the injectors when someone is cranking it?



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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.



paulg
User

Dec 2, 2016, 7:15 AM

Post #5 of 41 (422 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

The fuel pressure is hard to measure - it's a throttle body with the pressure regulator integrated into the casting with the two injectors. There's no schraeder (sp?) valve that I can connect a pressure meter onto. I do agree that it FEELS like a pressure problem but I've changed out pretty much everything that might affect that....

When it cranks you can see the spray of gas (I used a timing light which worked OK-ish) - and little droplets of fuel can be seen on the butterfly - but it really doesn't want to catch till it gets a dose of gas.


Hammer Time
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Dec 2, 2016, 7:19 AM

Post #6 of 41 (415 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

I'm aware or how it is set up. They make an adapter that goes in place of the fuel filter that makes reading the pressure easy.

We need to know specifically how fast it is coming up to pressure and whether it is maintaining rest pressure.





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

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.



paulg
User

Dec 2, 2016, 8:08 AM

Post #7 of 41 (406 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

It looks like the local autozone has a loaner fuel pressure set with all the adapters - so with luck I'll pick that up at lunchtime and see what the story is.

I'm assuming that the best spot to connect it in is to replace the fuel filter, right? All the fuel lines are solid.

Thanks for your time - it's appreciated :)


kev2
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Dec 2, 2016, 9:42 AM

Post #8 of 41 (394 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

yes tap pressure at fuel filter.
Spend a few minutes checking why no CEL - bulb or fuse*. USE a test light as ALDL jumper advise if it flashes.
1990 is awhile back but I think there were 2 temp sensors on this engine series - and ECT is a critical sensor. At thermostat and between plugs 1&3.
You will want to repair the egr - A SIMPLE SYSTEM. The gang here can walk you thru it after the starting issue....


*I think cigarette lighter fuse....


paulg
User

Dec 2, 2016, 9:50 AM

Post #9 of 41 (392 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

The CEL is OK - it lights for the bulb test, and it lights after about 10 minutes of running if I have the EGR plugged in (it also idles badly from that point on, which is why I disconnected it :))

Pulling the codes gives precisely nothing until the EGR code trips.

I changed the sensor that's close to the thermostat - you're saying there's another one?


Tom Greenleaf
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Dec 2, 2016, 11:37 AM

Post #10 of 41 (381 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

CTS near T-Stat should have the black and yellow wires to it so you know OE it was, replacement with plug may not and get a plug/pigtail if you do.


EGR is supposed to be 100% off at idle so may be leaking? Spray around it when it is running at idle plugged in or not it shouldn't react to being sprayed with like carb cleaner. If so diaphragm may be NG and or other issue and sending wrong pressure backwards? Worth the check.


CTS - without specs at hand you can just watch with an OHM meter it change from stone cold engine to a warmed up one changes in gradients. If it somehow always thought you were warmed up already it wouldn't start for crap. Plug itself used to always come with those because of failure so at least check that connects and doesn't look lousy for any reason,


T
PS: I'll let you search out a fitting for fuel filter that goes in line with a hose tube off of it to check pressure or vacuum once made by Snap-On (rip off) came in the kit might be sold separately??



(This post was edited by Tom Greenleaf on Dec 2, 2016, 11:40 AM)


kev2
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Dec 2, 2016, 1:54 PM

Post #11 of 41 (372 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

ok a 1990 C1500 with a 4.3L V6 or a 5.0 5.7L v8 ? pretty much the same but worth knowing...
EGR plugged in after 10 minutes what code do you get?
>> when you disable EGR you unplug the elec or vacuum?
ECT sensor at T'stat - 2 wires, with it plugged in what is the voltages on the wires? yellow? blk?


Tom Greenleaf
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Dec 2, 2016, 2:33 PM

Post #12 of 41 (363 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

OK - CTS or ECT can be called either just know the one near the thermostat usually and all I've seen from around there were yellow wire and black. None just showed that for a pig-tail replacement either blue and black or both black - nuts.


I'll try not to be wrong but if unplugged it would think it's fully warmed up and add no extra fuel which it must if cold or would require the prime of gas manually if cool enough ambient temperature or a real extended cranking.


This chart shows ohms to the exact temp. I don't buy needing it so precise just it works or thinks it's always -40F or essentially warmed up.


Chart is this showsCrazy
Coolant Temperature Sensor Diagnostic Test CTS

If you get a CTS error code or suspect it to be bad it can be tested with a multimeter set to OHMS. Here's the readings, it should match the outside tempreture if the engine is cold.

Coolant sensor approximate resistance specifications:
177 ohms @ 212 deg. F. or 100 deg. C.
241 ohms @ 194 deg. F. or 90 deg. C.
332 ohms @ 176 deg. F. or 80 deg. C.
467 ohms @ 158 deg. F. or 70 deg. C.
667 ohms @ 140 deg. F. or 60 deg. C.
973 ohms @ 122 deg. F. or 50 deg. C.
1188 ohms @ 113 deg. F. or45 deg. C.
1459 ohms @ 104 deg. F. or 40 deg. C.
1802 ohms @ 95 deg. F. or 35 deg. C.
2238 ohms @ 86 deg. F. or 30 deg. C.
2796 ohms @ 77 deg. F. or 25 deg. C.
3520 ohms @ 68 deg. F. or 20 deg. C.
4450 ohms @ 59 deg. F. or 15 deg. C.
5670 ohms @ 50 deg. F. or 10 deg. C.
7280 ohms @ 41 deg. F. or 5 deg. C.
9420 ohms @ 32 deg. F. or 0 deg. C.
12300 ohms @ 23 deg. F. or -5 deg. C.
16180 ohms @ 14 deg. F. or -10 deg. C.
21450 ohms @ 5 deg. F. or -15 deg. C.
28680 ohms @ -4 deg. F. or -20 deg. C.
52700 ohms @ -22 deg. F. or -30 deg. C.


Sorry - lots of info per degree. I've never found this just works or doesn't and plug to it or wires was the problem if this at all.
Did look and parts are a stock item for combo with pig-tail or separately. Short bucks as things go but test it! Test away as knowing it's wrong or not is good info,


T




Hammer Time
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Dec 2, 2016, 4:13 PM

Post #13 of 41 (357 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  


Quote
I'll try not to be wrong but if unplugged it would think it's fully warmed up and add no extra fuel which it must if cold or would require the prime of gas manually if cool enough ambient temperature or a real extended cranking.


Exactly the opposite. Unplugging the sensor creates open circuit and signal -40F to the computer will will cause a very extreme rich mixture.


I don't know if you have access to an OBD1 scan tool but looking at the sensor data would quickly tell you if you have a temp sensor problem. If the truck hasn't been started yet, the CTS and IAT should read exactly the same.



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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.



Tom Greenleaf
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Dec 2, 2016, 9:11 PM

Post #14 of 41 (350 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

Somehow I knew I'd have that backwards. Back to check for voltage passing thru the thing. It won't be 12V.


I have the scan tool quite dusty now but it just makes the CEL blink and get the # by counting the blinks should pick up a bad one but doesn't know if the item or the wiring to and from it IMO more likely if at all.


It's the equivalent of a choke for a carb sensing temperature. Add fuel when cold and don't add too much when warmer and tells even OBDI systems when it can do other functions like mess with the EGR or not until engine is warmed up and more. There's more electronic control of how it runs than you think for a 1990 and even older.


Did we clear up which engine this has? I saw even a 7.4, (454 CID) was available. All still need these things to work properly including EGR which also helps control engine knock at part throttle so this stuff is needed.


Need some info and observations posted - codes read can only help but limited. Parts tossing is NOT the answer,


T



paulg
User

Dec 4, 2016, 8:37 AM

Post #15 of 41 (332 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

Sorry - I wasn't clear, it's the 5.7.

I have tried unplugging the coolant sensor - on the basis that it would then fool the computer into assuming it was stone cold - and there was no difference in starting. It didn't turn on the CEL either, but I only had it unplugged while I cranked it over, so probably not long enough to register.

I do have an OBD1 reader - there are no stored codes. And the EGR valve is disabled by unplugging the valve electrically. Before I had the starting issue, if I had it connected, the truck would run fine, but when hot when I stopped at lights, etc, the idle was terrible - it would stumble and occasionally stall out.


Hammer Time
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Dec 4, 2016, 9:11 AM

Post #16 of 41 (326 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

It sounds like your EGR has some carbon caked up on the pintle holding it open. Why don't you just clean or replace it. That is a necessary component to the system.



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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.



Tom Greenleaf
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Dec 4, 2016, 9:15 AM

Post #17 of 41 (324 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

? Should have done something unplugging temp sensor? Test for any voltage going thru it use a "T" pin or a needle to touch back side it possible to keep it plugged in. I hate to may have to make the smallest prick in wires to test that way if so seal up even the tiny prick hole.
Still need the series of tests - fuel pressure that holds.


EGR: With it running spray around the thing either carb cleaner or brake cleaner it would change in front of you if leaking - gasket or diaphragm. If you just pulled up on that diaphragm with you fingers it should stall the engine right away.


If you try to clean it test it that it even hold vacuum you can do with your hands pulling it up and with finger block the ports and it should hold then when released back to OFF - sealed up tight. If you take it off there a cone "pintle" in side it that mixes spits of exhaust into intake air and fuel but not at idle or wide open throttle. You probably will need a new gasket if you take it off to try to clean a pintle cone pushing on it against wood with carb cleaner going thru it is about all you can do. IDK - most don't clean up but all this years ago for me on that one.


Trick: use a combo timing wrench to take those off helps! I think one nut is 1/2" and the other 9/16th" - don't bust those!


Use the high temp grease on those gaskets - just a smear and can be reused again later.


IDK why no codes? Not too surprised either as I didn't find OBDI very informative MOST of the time,


T



paulg
User

Dec 12, 2016, 6:11 PM

Post #18 of 41 (286 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

So today was the work xmas party, so I skipped out and I got the loaner fuel pressure test set from Autozone, and at $150 it'll be going back there tomorrow :)

And what a massive PITA that was to use. The throttle body adapter only fits when you have removed the fuel line clip from the bell housing, an operation that took nearly an hour. When it was installed it leaked gas EVERY which way, and only after we'd put petroleum jelly on the o-rings inside the adapter did we get the leaks under control.

And after all that? When the ignition is first turned on, there's 10 psi at the throttle body, which doesn't seem to drop much when cranking. It's tough to tell, because the pressure gauge is designed for much higher pressures so it's all at the bottom end of the range.

Since there is a hole cut in the bed to access the fuel pump, I thought I'd check there as well - and it was a little higher, maybe 11 psi if I squint hard.

Anyway, after an afternoon messing around with this thing, several cuts and about half a gallon of gas on the ground, I'm not sure I'm any better off. What do you all think?

I was sort-of leaning towards the flexible parts of the fuel hose collapsing, but given the pressure reading, and that it doesn't really drop when cranking......


Hammer Time
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Dec 12, 2016, 7:20 PM

Post #19 of 41 (282 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

The spec is 9-13 PSI so it doesn't sound like you have a fuel pump 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.



paulg
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Dec 12, 2016, 7:34 PM

Post #20 of 41 (278 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

Right, that was what I'd reckoned.

So my thinking goes that it has sufficient pressure at the TBI to work - it just "chooses" too lean a mixture. I'm pretty sure the temperature sender by the thermostat is OK - disconnecting it (and telling the ECM that it is way cold) doesn't affect the behavior. Also, I've replaced it AND measured the resistance so ....

So I guess my top question is "why is the mixture so lean"?

O2 sensor wouldn't do this, right? There's no MAF sensor that I know of.....


Hammer Time
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Dec 12, 2016, 7:46 PM

Post #21 of 41 (272 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

Are you sure both injectors are spraying properly?



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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.



paulg
User

Dec 13, 2016, 6:03 AM

Post #22 of 41 (251 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

Well, it's hard to know, because I'm not sure what "properly" means here, but there is a spray from each injector, and enough gas to form droplets on the butterfly valve.

Earlier I changed out the injectors, O-rings and filters for remanufactured ones so I'm pretty confident that isn't the issue.

To recap, here's what has been changed/checked:

New Delco fuel pump, strainer - and the rubber hose connecting the pump to the fuel pipe.
Fuel filter has been changed
Fuel pressure regulator
Both fuel injectors and filters on the nose of the injectors
Temperature sensor by the thermostat

Also - distributor cap, rotor arm and ignition module inside the distributor

There doesn't appear to be any codes stored - although ODB-1 means that's not all that surprising. The EGR valve has been bad for a while, and that hasn't been changed.

Once a cap of gas is poured down the throttle body, it'll fire up and idle nicely. It drives OK, although it feels very "flat" to drive - there's no get-up-and-go when you stamp on the gas. It restarts OK when warm.

Driving it to get the xmas tree, it stalled a few times in the grocery store parking lot when I was backing the truck out of the parking space - however, it ran OK on the way home.

I'm stumped.


kev2
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Dec 13, 2016, 6:50 AM

Post #23 of 41 (235 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

11psi is a good reading, have you checked for vacuum leaks - HT has mentioned the EGR being slightly open and vacuum leaks diaphragm or lines ...
us the old school spray trick easy fast and checp.... TBI base gasket, all vac lines. head to manifold gasket, PB line, MAP line, PCV stuck open,


Discretesignals
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Dec 13, 2016, 7:36 AM

Post #24 of 41 (228 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

I'd be looking at the injector pulse with a NOID light to see what happens when it is a cold no start. Seen that before in the past on those. The light should be flashing as the engine is cranking.





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paulg
User

Dec 13, 2016, 8:28 AM

Post #25 of 41 (216 views)
  post locked   Re: 1990 Chevrolet C1500 won't start when cold  

While I've not used a noid light on the injectors, I have looked at the pattern using a timing strobe, and it looked pretty good - there was a consistent spray, and gas IS getting there when it doesn't start. I'm somewhat surprised that it doesn't fire eventually, since it does seem to spray quite a lot of gas while cranking....

One good thing - well, I guess - is that when it's cold, it really won't start. At all. You can crank till the battery goes dead, and she'll not fire up. That does make it reasonably easy to try stuff while it's in the failing state. Once it lights up though, and it's fine.






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