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89 chevy truck staling


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lhanddh
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Jan 16, 2010, 2:21 PM

Post #1 of 35 (7263 views)
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1989 chevy truck 1500 4x4 5.7 250,000 miles keeps staling after warm up when you come to an idle


Tom Greenleaf
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Jan 16, 2010, 2:52 PM

Post #2 of 35 (7257 views)
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Re: 89 chevy truck staling [In reply to] Sign In

At the miles and age it's open to about anything. If it can run well off idle I'd be looking for vacuum leaks first with the symptom of warm only as it would naturally have some extra fuel when cold to cover a leak for a while.

Do you know what's been done and how long ago on this?

T
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Long retired now


lhanddh
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Jan 16, 2010, 3:09 PM

Post #3 of 35 (7253 views)
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new moter and trans about 5 years ago, in the past 2 months i have changed all vacum hoses, egr valve ecm, tps, idle air control valve, compleat tun up, put it in a shop and had a compleat test done on it. all they could find was plug wiers and replaced them again. still same problem.


Tom Greenleaf
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Jan 16, 2010, 3:44 PM

Post #4 of 35 (7246 views)
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Ok: Vacuum leaks can still be gaskets not just hoses. I think this should be TBI = throttle body injected which could need cleaning - carb cleaner type thing. I shudder to say spray areas with carb cleaner for suspect leaks as it can catch fire so perhaps using brake cleaner or plain water would be safer if not accustomed to that. When and if a leak is found the idle will change.

Places to look/check are base gasket of throttle body and where intake meets heads. Also the EGR shouldn't react. Don't go nuts with sprays that could be flammable as they can flash as said so if you try that (your call) pin point one spot at a time - let dry and move on. I haven't used brake cleaner which can hurt paint and rubber items but most is marked not flammable - can't speak for every brand of anything. Water (easy on hot stuff) would be safest.

If in doubt - DON'T! Let a pro check it but so far it seems like a common vacuum leak to me,

T
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lhanddh
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Jan 16, 2010, 4:05 PM

Post #5 of 35 (7241 views)
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put all new gaskets and fuel regulator on tbi, i will try and check where intake and heads meet. thanks for the help.


Tom Greenleaf
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Jan 16, 2010, 4:48 PM

Post #6 of 35 (7233 views)
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Recheck torque on the new gaskets as some require it! If you find intake to head issue I'm pretty sure those are 9/16th and gently snug up if loose - center first, criss crossing sides just easy by hand till end bolts. It's an all iron engine and manifold I think (could be wrong) and tolerant. If not iron only use exacting torque specs and order - been a while and I don't have specs at hand.

Good basics to those engines, fundamentals date back to the Flintstones!



T
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lhanddh
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Jan 16, 2010, 4:58 PM

Post #7 of 35 (7228 views)
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thank you, i will try that tomarrow and let you know how it goes, and thanks again for your time.


Sidom
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Jan 16, 2010, 11:27 PM

Post #8 of 35 (7218 views)
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Just a quick check. Disconnect the vacuum from your EGR valve and see if it makes a difference on your problem.
I see where you changed it but try it any way, it just takes a minute..........






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lhanddh
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Jan 19, 2010, 1:33 PM

Post #9 of 35 (7206 views)
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havent been avoiding you, took truck back to shop that worked on it, dumd asses ran the plug wieres across the ex. manafold and bund them up.they said they would fix them and check the rest out for free. i will let you know what i find out. and thanks again for your time.


lhanddh
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Jan 21, 2010, 5:27 AM

Post #10 of 35 (7199 views)
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they said the rod that goes through the tb tahd the tps is hooked to the hole is wore out and it needs a new tb. said that is where the vacume leek is.


Tom Greenleaf
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Jan 22, 2010, 6:40 AM

Post #11 of 35 (7188 views)
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If you carefull spray some carb cleaner at suspect area away from norm air intake and idle changes for better or worse there is a leak there,

T
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Long retired now


Loren Champlain Sr
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Jan 25, 2010, 9:26 PM

Post #12 of 35 (7174 views)
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Throttle body worn out?Unsure It's possible, but if the engine is running lean, you'll be able to suck in liquid most anywhere. These had a problem with 'sucking in' the TBI to manifold gaskets.
To add; If the throttle plate bushings are worn, they can be replaced without having to replace the TBI.
Loren
SW Washington


lhanddh
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Jan 27, 2010, 3:25 PM

Post #13 of 35 (7156 views)
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thank you, sprayed all around intake, throttle body, egr, and the idle did not change at all.


Tom Greenleaf
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Jan 27, 2010, 7:52 PM

Post #14 of 35 (7149 views)
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A maybe: The EGR has a pintle which seals it shut when cold (or supposed to) and at idle. This could not be sealing tight unseen without taking it off and cleaning it. A new gasket may be required and if you use some high temp silver grease on new gasket it usually will come apart and be reusable.

This pintle is essentially like a needle valve for a carb. It allows some exhaust gasses to enter incoming new mixture to cool oddly the temp of combustion to lower emissions. They don't always seal tight and it shows at idle speeds when it should be sealed tight.

That would be consistent with it only having a problem when warm as there's enough extra fuel while cold to cover it and not when warmed up.
When removed it may look like this one with the pintle hidden in this example. It's just a cone usually to block the passage of gasses when not called for and sometimes can get deposits on it and not seal. Carb cleaner and strong solvents can clean them up while off vehicle. They should be spring loaded to be shut and vacuum opens them when it's called for. It shouldn't work when cold, idling or full throttle and load. It wouldn't show up with it installed with any spray tests. For the price of a gasket it's worth looking at and attempt to clean IMO with the complaint of stalling you have, T
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lhanddh
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Jan 28, 2010, 6:49 AM

Post #15 of 35 (7141 views)
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ok, but i have already replaced the egr valve with a new one about a month ago, could this have alredy cloged up, and if so is there somthing i can change to stop this from happening again.


Tom Greenleaf
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Jan 28, 2010, 6:56 AM

Post #16 of 35 (7138 views)
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Not likely - sorry if I missed that,

T
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lhanddh
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Jan 28, 2010, 6:17 PM

Post #17 of 35 (7132 views)
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THATS OK, I THANK YOU FOR YOUR ADVICE ANYWAY.


lhanddh
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Jan 29, 2010, 7:15 PM

Post #18 of 35 (7117 views)
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with it being a new EGR could it still be a bad one without it flashing a code for the EGR valve.


lhanddh
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Feb 6, 2010, 3:01 PM

Post #19 of 35 (7085 views)
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does anyone know, is it posible that it is the o2 sensor causing the problem.


lhanddh
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Aug 7, 2010, 10:27 AM

Post #20 of 35 (5949 views)
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Ok, im back. Thanks for all the advice. Truck is running alot better. Now it is flashing code 43 electric spark control. I have replced the electri spark control, the speed sensor, a compleat throtol body unit with all new sensers, oxgen sensor, computer,and all vacume hoses.still flahing same code. The truck rus good at an idel andgoing down the road but go between 25 and 45 mph and it starts surgen, or like loping and will stall, if you let your foot off the gass it goes back to ideling fine, or if you put your foot into it it smooths out and takes off like there is no problem. Just put on new plugs, wires, cap and roter. still same problem


(This post was edited by lhanddh on Aug 7, 2010, 5:00 PM)


lhanddh
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Aug 14, 2010, 3:25 PM

Post #21 of 35 (5924 views)
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well, 7 days later and no replys i guess evryone is as stumped on this one as i am, well thanks anywayFrown


Tom Greenleaf
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Aug 15, 2010, 7:09 AM

Post #22 of 35 (5684 views)
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Long thread and sorry if I missed it. At 250,000 miles the timing chain could easily be way over spec for lash. Short of just going in there to see try putting timing on a known like TDC turning crank bolt in one direction and stop. With dist cap off see how many degrees engine turns by hand at that bolt before rotor turns. More than 5 degrees is trouble.

When they are way off they can jump and go back. Usual initial symptoms are backfires, loss of power and staggered misfires and perhaps snap right out of that.

Hey - it's a guess when you've checked everything with a high mile engine this can be the kicker. May or may not show with other routine tests and codes aren't likely to help except those that can say random missfire perhaps.

If you know it's original it is junk - trust me. 99% of ones I have done were because I was close anyway for another reason like a water pump and vehicles with over 100k to be kept I just asked if they wanted the next item in as the labor was mostly done.

Just once I was shocked to remove an OE timing chain at over 100k that really was good. Nylon geared cam geared (OE one) so did it anyway as it not big bucks,

T
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Long retired now


Sidom
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Aug 15, 2010, 8:05 PM

Post #23 of 35 (5675 views)
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As you know that code is for the electronic spark control. There is a problem with your knock sensor circuit. Basically when there is a knock the ESC sends a signal to the PCM and it retards the timing.... When the signal is there for too long the code is sets.

If I remember correctly the signal wire has 12v on it and the ESC pulls the voltage down when a knock is detected. These weren't the best sensors and anything could generate a signal.

So 1st off if there is any mechanical problem going on making a noise, that would need to addressed.... Tom already mentioned some....

After than you need to get a diagram for the circuit and check voltages and make sure the knock sensor can generate a signal....

I'm a little data challenged at the moment so I can't post anything but if you really need something, I might be able to get something from work....

I don't know what you have tool wise but a scanner & scope really makes checking this problem out A LOT easier.......


Just a quick thought..... A good short cut would be to get a diagram find the circuit that goes from the ESC to the PCM, disconnect both connecter & check it with an ohm meter to make sure it isn't open. Then find the circuit going from knock sensor to the ESC, make sure it isn't close to any plug wires......After that you need to start at square 1......






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lhanddh
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Aug 15, 2010, 9:22 PM

Post #24 of 35 (5670 views)
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moter and trans was replaced about 6 years ago,has about 60,000 miles about 3 monthes ago replaced the distributor. Is it posibale it could still be in the timing chain. I will check like you said, thanks for the help.


lhanddh
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Aug 15, 2010, 9:25 PM

Post #25 of 35 (5669 views)
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I will try these and get back to you and let you know how it turns out, and thanks again
cant find where the knock sensor is, book has it in front of the starter, there is nothing there.


(This post was edited by lhanddh on Aug 19, 2010, 9:28 PM)




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