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1990 c1500 with possible fuel issue


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zboy56
User

Dec 16, 2012, 10:08 PM

Post #1 of 42 (2924 views)
  post locked   1990 c1500 with possible fuel issue  

My 1990 c1500 has been attacking up lately but only when it's near freezing or below outside. It has 5.7 v8 engine and it's fuel injected. sometimes i'll start it and will idle very rough and bog down then stall but will start up again and have to the gas peddle to keep it running also as i down the road it will bog and have almost floor it before it will power again and accelerate. I have recently replaced the fuel filter and have checked for fuel leaks or pinched lines and there are none.


nickwarner
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Dec 17, 2012, 4:07 AM

Post #2 of 42 (2879 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

are there any trouble codes stored? You don't need a scanner to view them with this truck, just a paper clip between ports A and B of the ALDL connector will let you get blink codes from the service engine light. What is your fuel pressure at? You would need a gauge with the proper adapter to tee into the pressure side. Shold be between 9-13psi. Check that the injectors are spraying properly too. Take off the air cleaner and have someone start it while you look down the throttle body at the two injectors. They should both be spraying a fine mist. If you see one that dribbles a bit you know you have a bad one. If you're not finding it from those tests, you would want to get ahold of something that is able to link up to an OBD1 system and show data. I'd be curious what the coolant temp is reading while cold. Should mirror the IAT reading prior to startup.


zboy56
User

Dec 17, 2012, 8:30 AM

Post #3 of 42 (2865 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

ok where is this ALDL connector located at and where will the a and b ports be at on it?


zboy56
User

Dec 17, 2012, 2:45 PM

Post #4 of 42 (2855 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

i've checked the fuel injecters and they are working like they should but i don't have any way to get a something that will show the data you want i stopped at the part stores around here but their code are only for check engine light problems and the only comes on when the truck dies so they can't help.


nickwarner
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Dec 17, 2012, 4:36 PM

Post #5 of 42 (2851 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

The diagnostic port is underneath the dash to the left of the transmission tunnel. Terminals A&B are top right two. If you put a jumper between them it goes into self diagnostic to display codes using blinks of the check engine light. You put in the jumper with the key off, then turn the ignition to key on, engine off. The engine light will flash each code 3 times in a row, starting with a code 12. That tells you it is about to show the codes and the diagnostic mode is working. When it has shown all the codes three times, it will again flash the code 12 three times to tell you that it has shown you all the codes in memory.

Without the benefit of a scan tool to show data we'll have to do things the old-fashioned way. The coolant temp sensor should be on the front of the intake manifold in the coolant passage and will have two wires. You can measure the resistance of the sensor and see if it changes with engine temp. I don't have the chart myself, but one of the buys here has a chart that shows ohm readings in relation to the temperature that would give you an idea if its reading right. If they come across this thread I'm sure they'll post a chart.If its way off you'll get a code 14 or 15 when you pull the codes.

Other things to look at are vacuum leaks. With the age of this truck you most likely have a few and they can add up to enough of a leak to cause bad gas mileage and driveability issues. One method I like to use is to put a piece of rubber hose on a propane torch. Start the engine and let it run. Turn on the gas and slowly move the hose around the throttle body base, intake manifold, brake booster and such. You may need to take the serpentine belt off so that your engine fan doesn't blow the gas away. Remember then to only run it for a minute or two so you don't overheat anything or kill the battery. If the RPMs suddenly go up, you've found the leak where the hose is. On the upside, parts are dirt cheap for your engine and its about the simplest truck to work on.

One cheap thing you should do now is to change all your vacuum hoses. You can buy it cut from a bulk roll at parts store for very cheap. Get about 4 feet of the main three sizes and a razor blade. The old hose likes to stick so slit the side of the hose where it hooks up and it will pull off easy. Change one hose at a time so you don't get anything mixed up. Those hoses are old enough to walk into a bar and are just cheap rubber. Most likely they're weatherchecked and leaking a bit of vacuum. Even if it doesn't fix this problem, its going to save you problems down the road for sure.


zboy56
User

Dec 17, 2012, 11:22 PM

Post #6 of 42 (2837 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

well strangely the fuel mileage seems not to be effected by this problem but i'll check to see if any codes come up tomorrow from that test and all the hose appear to be fine no cracks or anything in slightest bit wrong with them


(This post was edited by zboy56 on Dec 18, 2012, 12:58 PM)


zboy56
User

Dec 18, 2012, 1:16 PM

Post #7 of 42 (2817 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

i connected to the a and b ports like you said to do but all it did was flash the 3 times and pause and then flash it 3 times again and pause and it repeated that about 5 times so then i turn the key off and took the thing of the ports


nickwarner
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Dec 18, 2012, 3:02 PM

Post #8 of 42 (2813 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

Thats a code 12 so you have no codes in the ECM. You count them by the spacing between flashes. Flash, pause, flash flash, pause.

Have you checked for vac leaks around the gaskets with the propane yet?


zboy56
User

Dec 18, 2012, 4:43 PM

Post #9 of 42 (2808 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

i have checked the hoses but not with a torch because i don't have one but they all appear to be fairly new there aren't cracks or anything that would indicate air could escape from them, no sounds or anything like that coming from the engine compartment that would make me think there is a leak


nickwarner
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Dec 18, 2012, 5:55 PM

Post #10 of 42 (2802 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

a few small leaks won't make an audible noise. Looking just at the outside of a line isn't the same as visually inspecting it for dry rot which can come from the inside. Thats why I said to just change the things. Best ten bucks you'll ever spend. You need to get in there and test it according to the info I've already given you.


zboy56
User

Dec 18, 2012, 6:13 PM

Post #11 of 42 (2801 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

ok, there is supposed to snow and windy condition here the next 2 days and i don't have garage to work in so that will have to wait until this weekend but i'll post a message if any thing changes with this problem i'm having


zboy56
User

Dec 18, 2012, 7:50 PM

Post #12 of 42 (2794 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

i didn't know if this would help you with trying to help me figure out the problem is or not but my truck seems act up the most after its heated up and then sits with the engine off long enough for the temp to fall back down to about 140-170 degrees f


Tom Greenleaf
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Dec 19, 2012, 5:07 AM

Post #13 of 42 (2778 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

Here's that chart for the Engine Coolant Temp sensor............


In that you haven't noticed unreal lousy fuel economy and no codes it's probably fine. This vintage of vehicles can have issues and not throw codes so you end up testing stuff in assorted ways. If some sensor is sending credible but wrong info they don't know anything is wrong.

Long enough read here already. I'd be thinking fuel delivery also. Any vacuum leak can fool it, not just hoses but throttle body gaskets, intake manifold gaskets could be engine temp sensitive and not show at certain times. That crap causes one to pull hair out as things may test OK and aren't,

T


zboy56
User

Dec 19, 2012, 2:19 PM

Post #14 of 42 (2766 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

when i was looking under the hood today i noticed that the, i believe it was called, throttle body intake gasket was all but gone so replaced that but because this is a intermittent problem i'll wait i few days before i say that fixed it or not


(This post was edited by zboy56 on Dec 19, 2012, 4:28 PM)


Tom Greenleaf
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Dec 19, 2012, 3:29 PM

Post #15 of 42 (2759 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

Anything like that, that is allowing unmetered air in would cause problems. Hope that's it and you are all set for now,

T


zboy56
User

Dec 19, 2012, 3:58 PM

Post #16 of 42 (2753 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

well that didn't fix the problem but it might have helped because now anytime i start the truck with the temp around the 140 to 170 range it will act up but not as badly Frown


Tom Greenleaf
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Dec 19, 2012, 4:06 PM

Post #17 of 42 (2742 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

There's a gasket set for the throttle body. I didn't see just one out there. If one was so lousy perhaps another. As said "unmetered air" is like the equivalent to any vacuum leak.

Plenty of things could still need checking. It's improved so sure seems like you are on to it,

T


zboy56
User

Dec 19, 2012, 4:29 PM

Post #18 of 42 (2731 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

ok it was the air cleaner gasket i replaced and are there any other gaskets in that area i should check


(This post was edited by zboy56 on Dec 19, 2012, 11:52 PM)


nickwarner
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Dec 19, 2012, 4:42 PM

Post #19 of 42 (2728 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

You need to go back to my earlier post about checking very carefully for vacuum leaks. Sounds like you have some. You can use carb cleaner if you don't have a small propane torch. But you need to look very closely.


zboy56
User

Dec 21, 2012, 6:35 PM

Post #20 of 42 (2690 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

 


(This post was edited by zboy56 on Dec 21, 2012, 8:39 PM)


nickwarner
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Dec 21, 2012, 7:32 PM

Post #21 of 42 (2684 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

humidity doesn't affect it


Tom Greenleaf
Ultimate Carjunky / Moderator
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Dec 21, 2012, 7:52 PM

Post #22 of 42 (2683 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

I'm going blind trying to follow this. Is this to say it does or doesn't act up based on humidity? Snow doesn't necessarily mean very humid. That post suggests that weather matters a lot. Of course all things working well weather, humidity shouldn't matter much. A vacuum leak probably wouldn't care so much about humidity - high voltage items, that is anything to do with spark is more sensitive to moisture/humidity.

Perhaps we are chasing the wrong things or there's a typo in there somewhere. If an engine runs well if known all dry then a spray test with just a tad of salt and water or I have luck with plain window cleaner (Windex) spot spraying suspect areas one by one and see if an area or item reacts to that. Some will plain arc in sight while damp to wet.

Gotta be careful with assorted test tricks for an intermittent problem trying to duplicate a problem no matter if chasing vacuum or electrical leaks. A hot engine isn't going to like being soaked or shocked cold. These funky tricks do come with some risks of hurting something.

Sorry if misread but if this can be that sensitive to humidity we need to look there.

High voltage items are things like distributor cap, plug wires, coil towers, plug wire boots and even the porcelain of spark plugs themselves. Technically called "secondaries" of the ignition system. New items or not can still fail. Ex: you don't pull on plug wires, drop spark plugs new or if out for any reason but when something just began with something new or messed with you would look there first.

Before we beat this to death is this humidity causing the problem?

Tom


zboy56
User

Dec 21, 2012, 8:38 PM

Post #23 of 42 (2674 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

sorry guys i meant to say it's not acting up at all now. it's almost like now that there is moisture in the air it sealed the leak or fixed the problem but as to i'm clueless


(This post was edited by zboy56 on Dec 21, 2012, 8:40 PM)


Tom Greenleaf
Ultimate Carjunky / Moderator
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Dec 21, 2012, 9:03 PM

Post #24 of 42 (2669 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

An intermittent problem is going to be a pest. By all rights so called moist air shouldn't make it better. Some vacuum leak issues can be a split in a hose, hose elbow or some diaphragm somewhere and not cause an issue all the time.

Dang it's hard to fix what ain't brokenMad IDK - try wiggling things keeping your hands out of harms way and something might change in front of you. If nothing you may have to wait for it to act up again??

T


zboy56
User

Jan 10, 2013, 10:37 PM

Post #25 of 42 (2606 views)
  post locked   Re: 1990 c1500 with possible fuel issue  

well guys i finally figured out what the problem was with my truck, one of the spark plugs had crack in the insulator but the boot was holding it together






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