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Stalling When Hot

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SurfinCR

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So this isnt for a k5 but it is for a chevy. before i start throwing a ton of money at the truck i wanted to ask here. i have an 88 c2500 350tbi and 700r4 tranny w/92k miles on it that runs good when it first starts (it does need new valve seals and possibly rings as it give a nice blue cloud at first start) it will run fine until its up to operating temp then if i stop she will randomly die. i cleaned the egr which was stuck and did have a vacuum leak at the hose. fixed a leaked at the canister. this weekend it started do it so i popped it into neutral and the engine started to shudder off and on but didnt want to die. it feels to me like its missing but i'm not sure. if i keep on the gas it will run fine again. my first instinct is to replace the coil as plugs, wires, points, and condensor were replaced maybe 40k ago.


Any help is much appreciated.
 
Follow these directions:

1. Check the codes. You can do this by putting a paperclip in the port under the dash, and it will tell you what is wrong. Directions are in the Injection section (sorry, I don't have access, so no link! :( )

2. Fix what is broken.

Do anything else and you are likely wasting money, time, and energy not fixing the problem.
 
All the HEI stuff (coil included) can be properly tested other than plugs and wires which IMO can be flakey enough to cause issues that wouldn't be found in testing. Those should be replaced at a specific interval or when it's obvious they are shot. If routed properly, and good wires, I'd say 40K is low for replacement, but that's me. If they are bad, normally a light show at night, underhood, is easy to see. My motto is don't replace ANYTHING until you have completely diagnosed the problem, unless you already have a known good spare that will cost you nothing to swap.

No points and condensor, so not sure what you mean there...module, pickup coil maybe?

Codes don't tell you what is wrong, it tells you what sensors the ECM thinks aren't seeing proper values. Low O2 voltage doesn't mean the O2 sensor is bad, it could be an exhaust leak, bad injector(s), etc. Codes can help narrow down an issue, but that's it.

One thing on TBI that never hurts to check is the TBI to intake gasket. They seem to be pretty prone to cracking and creating a vacuum leak.
 
dyeager535 said:
All the HEI stuff (coil included) can be properly tested other than plugs and wires which IMO can be flakey enough to cause issues that wouldn't be found in testing. Those should be replaced at a specific interval or when it's obvious they are shot. If routed properly, and good wires, I'd say 40K is low for replacement, but that's me. If they are bad, normally a light show at night, underhood, is easy to see. My motto is don't replace ANYTHING until you have completely diagnosed the problem, unless you already have a known good spare that will cost you nothing to swap.

No points and condensor, so not sure what you mean there...module, pickup coil maybe?

Codes don't tell you what is wrong, it tells you what sensors the ECM thinks aren't seeing proper values. Low O2 voltage doesn't mean the O2 sensor is bad, it could be an exhaust leak, bad injector(s), etc. Codes can help narrow down an issue, but that's it.

One thing on TBI that never hurts to check is the TBI to intake gasket. They seem to be pretty prone to cracking and creating a vacuum leak.
Click to expand...

points and condensor you're right, for some reason that stuck in my head as being replaced. too early on monday for my brain to fucntion properly.


The truck did sit for long periods of time so that would make sense that the gasket could be shot. i'll have to check this week.
 
My truck sits a bunch too, and the pickup coil was a mess when I had to replace it...I am surprised it lasted as long as it did. But again, most of this stuff can be tested. Make sure you take a look at all your vacuum hoses and electrical connectors/wiring while you are underhood, might be something even more simple.

Vacuum hoses really need to be replaced every so often as well, if they are showing cracks, time to replace.
 
so i'm back to the drawing board. all the hoses look great, checked the codes and nothing came up. attempted to see if the spark plug boots were bad last night but the truck decided it would run perfect.. go figure. i'm wondering if it could be the air sensor in the tbi?
 
I just had this problem as well as low power from the engine. The coil wire was sparking as it sent a spark to the cap and melted the boot enough that it was grounding out. New plug wires with dielectric Grease to Make sure It Could Only spark to the wire itself. Fixed. Just check That the wires are all the way on correctly if they still look good. Pull a spark if and see what they look like. That will tell a lot.
 
have you checked the IAC? when you start it does idle high then gradually drop back to the normal idle?.
 
blaznjon said:
have you checked the IAC? when you start it does idle high then gradually drop back to the normal idle?.
Click to expand...

that is actually what was on my list to check next.

When cold it actually does idle rather high (no idea how high as the truck doesnt have a tach) then when it warms up part way it goes to a normal idle then when fully hot it starts acting up.
 
Really need to get a scanner on the motor (or laptop/ALDL cable/tunerpro RT) to look at this stuff real time.

Seeing as it does it when the engine warms up, sounds like something that is occurring after it goes closed loop, when the O2 sensor starts trying to "fix" fuel delivery based on what it's seeing in the exhaust stream.

No exhaust leaks?
 
dyeager535 said:
Really need to get a scanner on the motor (or laptop/ALDL cable/tunerpro RT) to look at this stuff real time.

Seeing as it does it when the engine warms up, sounds like something that is occurring after it goes closed loop, when the O2 sensor starts trying to "fix" fuel delivery based on what it's seeing in the exhaust stream.

No exhaust leaks?
Click to expand...

there is a leak between the manifold and pipe. i actually keep meaning to fix but havent had time and not sure of the best fix since the bolts are pretty much shot.
 
Anymore I think I'd try this stuff on the bolts https://weldingsupply.com/cgi-bin/einstein.pl?PNUM::1:UNDEF:X:05222 before trying to loosen them, and just be prepared to use an oxy/acetylene torch on any that break off in the manifold. Or just go headers :)

In this case, need to fix that issue before doing anything else, no further diagnosis needed/warranted. It is possible that it's messing with the O2 sensor. May or may not be causing the problem, but its definitely not right, so fix that first, see if problem goes away.
 
Electronics can act funny when they get warm. Don't rule out the ignition module (mine acted up when warm, but I think my arcing coil and wires helped get it to that point). Someone on here mentioned that their parts store was friendly enough to allow them to "test" a new one before (however, most electronics are usually non-refundable once installed).
 
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Pop your distributor cap and look at your pick up coil. If it looks like it is falling apart it needs to be replaced. You do have to pull the distributor to replace the pick up coil.

Wiggle the two wire ICM to Ignition Coil wire when the engine is running to see if that is tight.

If you do end up replacing your pick up coil make sure the pick up coil to ICM wire can't reach to the edge of the dist cap. If those wires get pinched, you will start having troubles down the road. Twist the wires so the bunch up a bit and then plug it into the ICM. That keeps the wires from getting under the cap lip.

The pick up coil looks like this - (blocked by the forum) search for it on Rock Auto

Does the truck have a tach? Does the tach fail when the engine fails? If so that indicates a problem with your primary ignition components.
 
No tach on it, unfortunately is the absolute AT base model c2500 ext cab w/ long bed. so it doesnt have any of the good stuff.

unfortunately it decided to pour here last night so i still wasnt able to check anything, but i definitely have a list of things to check.
 
so i decided heck with it , while i'm cleaning the iac valve i'm going to rebuild the tbi and since found a coupon for advance i'll be replacing the coil as well.

hopefully i'll report back after
 
So i rebuilt the TBI, swapped the coils and cleaned the rather dirty IAC valve the truck seemed to idle a lot better. took it for a test drive and it actually seemed to run better. i didnt have any issues with it stalling however saturday the temp was only around 80 and was really only having a problem when the temps were in the 90's.

the one thing i did notice is after reving it and letting it come back down it would shudder and then be fine at idle.

i noticed the spark plugs were pretty rusty and had some new plugs (ac delco ac1 ) so i swapped those in. the truck now has a much more noticable shudder when idling. Any thoughts on what would cause this?

going to take the truck for a ride today to check the stalling issue as its going to be hot enough.
 
the good news is i took it out in the 96+ degree weather and for the first time it really did not want to stall. it still seems to have something off so nexts steps are going to be fuel pump & relay, along with new plug wires and headers since i dont want to mess around with the rusty manifolds
 
just in case anyone is following this or in the future has a similar problem. the truck is definitely running better over all however after running it in 90+ weather i got back home went to shift into reverse and the engine died. so its still back to the drawing board. next up is going to be the fuel pump since both times i worked with the fuel system there was no pressure in the lines.
 
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