1993 Chevy K3500 - Rough idle and stall

[PlayingWithTBI]

I'm not saying this is your problem; I had issues with my engine surging while cruising. According to my data log it would jump to as high as 4600RPM when cruising at ~2200 (which is impossible). The ECM sees the jump in RPMs and throws fuel at it causing the surge.

I've read where other members had issues like this at idle (I'm seeing more and more cases of this). Turns out it was the ICM in the distributor (only 3000 miles old). I bought an AC Delco ICM and used MX-4 compound. Now it runs smooth at all speeds.

The point is data logging didn't show the ICM or ignition for that fact was bad but, it did show a weird anomaly. Sometimes you just gotta guess. HTH

https://www.summitracing.com/parts/ado-d1984a


https://www.amazon.com/gp/product/B0795DP124/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1

 

[JWAZ73]

Thanks, I'll look into it further.

I was looking at the scan data I collected last night and noticed the automatic spark advance was almost 17 degrees advanced of TDC. Is this a normal range?

UPDATE:
Answered my own question, these timing values align with the values in the .bin file tables...

 

[Schurkey]

Using a hand vacuum pump I tested the EGR and EGR solenoid, they behaved properly according to the Haynes.

That's OK, but an EGR valve can stick open at idle, making a mess of vacuum readings. If there's any carbon stuck to the valve pintle, it can prevent the valve from fully closing. Might be worth your time to remove the valve from the manifold and inspect the valve and manifold visually.

Testing the O2 sensor, key on and engine not running the sensor voltage from TP was about 430mV (Haynes says it should be between 400mV and 500 mV). Engine running at idle, sensor value was all over the place, the low I saw was about 300mV and the high was in the low 600mV range (Haynes says this should be between 100mV and 900mV and it should fluctuate). O2 sensor seems to be fine.

The low range is high, the high range is low. The sensor MAY be reporting accurately, but I have a hunch that says the thing is slow and lazy and staying too much to the middle of the range.

I don't expect that's the rough-idle problem, though.

@Schurkey, to answer your question about fuel, I don't see a sensor in TP for fuel pressure and I don't have a tool to test it. I will have to borrow a tool from the parts store to do that but that's not a bad idea. As far as the fuel pump and filter, they both were replaced by the previous owner when he was trying to get the truck to run before we took possession of it. They have less than 1000 miles on them.!

A thousand miles is more than enough to destroy a fuel pump if it got contaminated by a rusty, dirty fuel tank. Grit going through the pump is the number one killer of replacement pumps.

There's also the possibility of an electrical failure causing the electric motor of the pump to not spin at an appropriate speed. The wire harness back to the battery (positive and "ground") could be suspect.





What are your short- and long-term fuel trims?
Coolant temp sensor accurate? Does it show ambient temperature after the engine has been shut-down overnight?
And I'm still curious about the compression-test results.

 

[JWAZ73]

@Schurkey, here are the compression numbers by cylinder:
1 - 160
2 - 170
3 - 165
4 - 160
5 - 160
6 - 160
7 - 160
8 - 170

I'm not sure how to look at the fuel trims but I'll research that. If you know how to do that with TunerPro RT, I'm all ears... The coolant sensor does read at ambient temp once the engine has cooled overnight.

Sorry for the length of this but I need to provide a bit more background on this issue. I thought I had solved this already but it was suggested to me today that it may still be THE problem...

When we first got the truck it would get very hot then the thermostat would open and it would run at a more 'normal' temperature. I thought that sounded like a sticking thermostat so I set out to replace it. Regardless of how careful I was, I managed to break one of the thermostat housing bolts. Now I have to remove the intake so I can get bolt drilled out and re-tap the hole. The intake should have 12 bolt holes on it, the four center holes did not have bolts and were filled with orange RTV. Wait, it gets better... After getting the intake off I noticed that the four center holes did not align with the holes on the heads. They were the same size but were at a different angle. This caused me to look at the engine closer and after finding the casting number on the block I found out this is not the original engine but rather a 305 CI block for a 1996 - 1997 Vortec engine. Casting number 10243878. I called and talked to a support person at Summit Racing who was a big help in pointing out the intake I would need to bolt properly to these cylinder heads. He also told me that the geometry of the new intake was identical to the one that I had except for the angle of the four center bolts. He was happy to sell me $300+ in parts but, he said if I was comfortable with it, I could modify the bolt holes on this intake so they line up with the holes in the heads. That is what I did and it turned out nicely. Before reinstalling the intake I ran a tap into the bolt holes in the heads to make sure whoever did this engine swap didn't mess up the threads in those holes that were not aligned. The threads were fine. I used a gasket kit that included new plenum seals for the front and rear of the intake. I followed the instructions with the gaskets and used black RTV where indicated including a healthy amount on the plenum areas and torqued the intake down.

The conversation I had today was with the guy at the parts store who recommended the machine shop to me to fix the thermostat bolt hole. (He also tested the ICM for me and it passed.) He said that these symptoms still sound a lot like a vacuum leak and suggested I smoke test the intake system and verify the intake gaskets and plenum are not leaking. I should be able to do that in the next couple of evenings.

This is a prime example of free not being free. The guy we got this truck from told my son that if he could drive the truck off his property that he could have it. And that's what we did... This is a lot more than either of us expected. This has the potential to be a great truck and when we are done there won't be any part of this engine that he (or I) will not have an understanding of.

 

[Schurkey]

@Schurkey, here are the compression numbers by cylinder:
1 - 160
2 - 170
3 - 165
4 - 160
5 - 160
6 - 160
7 - 160
8 - 170

That seems fine, if anything it's high--but they're even enough.

I'm not sure how to look at the fuel trims but I'll research that. If you know how to do that with TunerPro RT, I'm all ears... The coolant sensor does read at ambient temp once the engine has cooled overnight.

I can't help you with TunerPro.

When we first got the truck it would get very hot then the thermostat would open and it would run at a more 'normal' temperature. I thought that sounded like a sticking thermostat so I set out to replace it. Regardless of how careful I was, I managed to break one of the thermostat housing bolts. Now I have to remove the intake so I can get bolt drilled out and re-tap the hole.

Why? I'd drill the thing in-place. You do it right, (and that takes some skill and some luck) you'll peel the bolt threads out of the hole like they were a heli-coil.

[EDIT]Never mind. Pull that intake manifold off. You need to have a machinist check the gasket surfaces for straightness and flatness and smoothness.[/EDIT]

The TBI engines tend to have a bunch of ground wires that are attached to one or the other of the thermostat bolts. You didn't leave those loose, right?

The intake should have 12 bolt holes on it, the four center holes did not have bolts and were filled with orange RTV. Wait, it gets better... After getting the intake off I noticed that the four center holes did not align with the holes on the heads. They were the same size but were at a different angle. This caused me to look at the engine closer and after finding the casting number on the block I found out this is not the original engine but rather a 305 CI block for a 1996 - 1997 Vortec engine. Casting number 10243878.

I didn't realize that the 305 Vortec had 6-bolt (12 bolts altogether for the intake manifold) heads. I figured they were 4-bolt like the 5.7 Vortec heads. Or do you have "old" heads on a 96+ Vortec 305 block?

WHAT INTAKE MANIFOLD DO YOU HAVE? Photo? I looked at putting an OEM TBI intake manifold with the more-upright center bolt holes onto a pair of heads intended for '85--older engines. I wasn't willing to grind the holes oblong, because the underside of the intake manifold casting didn't look like there was enough material to grind the holes far enough over to make it fit. OTOH, I do have an intake manifold for the older heads that's been ovalled at the center holes to make it fit the TBI-style upright center bolt holes.

You replaced the injectors. Did you use 305/5.0L injectors, or are you over-fueling the engine with 5.7L injectors?

I used a gasket kit that included new plenum seals for the front and rear of the intake. I followed the instructions with the gaskets and used black RTV where indicated including a healthy amount on the plenum areas and torqued the intake down.

"Plenum areas"??? WHAT "Plenum areas"? Do you mean the lifter valley?

Most guys refuse to use the rubber seals included in an intake gasket set. RTV Silicone, or The Right Stuff by Permatex (Urethane) are the preferred methods.

WHAT GASKET SET (Part Number) DID YOU USE? Were the rear water passages blocked off, or open?

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The conversation I had today was with the guy at the parts store who recommended the machine shop to me to fix the thermostat bolt hole. (He also tested the ICM for me and it passed.) He said that these symptoms still sound a lot like a vacuum leak and suggested I smoke test the intake system and verify the intake gaskets and plenum are not leaking. I should be able to do that in the next couple of evenings.

I still don't know what you mean by "plenum".

Testing an ignition module can tell you if it's bad. It can't tell you if it's good. It can tell you that it passed whatever the test is...but the module testing is crude.

A Tonner 4X4, with a 305 and probably 5.7L injectors? No wonder the fuel economy is in the toilet.

 

[JWAZ73]

@Schurkey, thank you for the detailed reply!

Here is a photo of the intake manifold before I cleaned it up. (broken bolt has already been extracted.)

The 'plenum' I'm talking about is the space beneath the intake where you can see the lifter rods.
I did use a gasket set that had the rear coolant channels blocked with only a small hole in the space. Here is a link to the gasket kit used: https://www.autozone.com/external-e...e-manifold-gasket-ms15401/148287_696806_12080

The fact that I bought injectors for what I thought was a 5.7L didn't even cross my mind. Brilliant suggestion! I see there are different part numbers for the 5.0L injectors. Unfortunately, I cannot read any part numbers on the ones I took out so I have no idea what they are. Anyway, I need to get the proper injectors for this displacement.

I know this is a newbie question but, would the injectors providing too much fuel cause the rough idle condition I'm struggling with?

 

[PlayingWithTBI]

I'm not sure how to look at the fuel trims but I'll research that.

Fuel trims are INT (short term) and BLM (long term). Stoich (14.7 AFR) is ~128, lower it's running rich, higher it's running lean. If you have 5.7 injectors in a 5.0 it'll run rich unless your PCM can trim enough fuel out of it, by reducing injector BPW (Base Pulse Width). Generally it can only adjust a small percentage. Watch your O2 sensor. If your trim is right it will go over and below 450 rapidly. Cross counts tell you how well it's working. The more you get the better. Oh yeah, INT is Integrator and BLM is Block Learn Multiplier.

Here's a screen shot from one of my logs.

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[PlayingWithTBI]

I know this is a newbie question but, would the injectors providing too much fuel cause the rough idle condition I'm struggling with?

That's a possibility.

 

[Schurkey]

The 'plenum' I'm talking about is the space beneath the intake where you can see the lifter rods.

Lifter valley.

Don't forget to have that manifold checked for straightness. Wouldn't surprise me to find it's warped, given that it was attached with only about 2/3 the required number of bolts. For that matter, if it wasn't sealing in the middle, there's a vacuum passage for the EGR that might have been sucking air.

If you flip that manifold over and look at those center bolt holes from the bottom, you'll see where the manifold has been cast with "hollowed-out" areas around the bolt holes. You grind the holes oblong, the manifold may no longer be strong enough due to the lack of material.

Somehow, you've got pre-TBI cylinder heads on a post-TBI block, using a TBI intake and injector system. This was not very bright on the part of the guy creating this Frankenstein's Monster. Perhaps his brain was Abbey Normal.

Now that I think about it, the Vortec 5.7 (and, I suppose, the Vortec 5.0) used a different coolant routing for the coolant bypass. I wonder how that was handled by the guy who put this together.

I did use a gasket set that had the rear coolant channels blocked

Excellent. That sort of gasket set is mandatory with the "stock" TBI intake manifolds.

The fact that I bought injectors for what I thought was a 5.7L didn't even cross my mind. Brilliant suggestion! I see there are different part numbers for the 5.0L injectors. Unfortunately, I cannot read any part numbers on the ones I took out so I have no idea what they are. Anyway, I need to get the proper injectors for this displacement.

Yup.

I know this is a newbie question but, would the injectors providing too much fuel cause the rough idle condition I'm struggling with?

It's certainly not helping. There may be something else wrong in addition...but we know that the injectors are wrong. Keep the injectors for when you upgrade to a 5.7 later on.

"I" would be looking for a complete TBI unit from a 5.0L of the appropriate year, on craigslist or a Treasure Yard, or whatever. There's got to be a zillion of them out there, and I bet you could get one for about $20. As long as the vacuum nipples that you need were there, you'd be set.

 

[JWAZ73]

Happy Friday friends!

This week got really busy at work and I haven't looked at the truck again until today. I connected my scanner to the truck and monitored the short and long term fuel trends (INT and BLM counters). Both were less than 128 but above 120. I went ahead and replaced the injectors with the appropriate injectors for a 305 block and both fuel trends stay at 128 now (at least for the 15 minutes I was watching it). This did not fix the rough idle problem. I talked to some folks at work who also play with engines. They all seemed to agree that this could be a vacuum leak or could be something else, but the first step is to prove that's it's not a vacuum leak. I hooked up the smoke pot, connected it to a vacuum inlet and began pushing very low-pressure smoke (<5 PSI) into the throttle body. Immediately there was smoke coming out from under the TPS. Using a mirror I looked under the TPS and saw the smoke coming out from around the 'gasket' that was around the stem where the throttle rod connects to the TPS. I removed the TPS and replaced that foam ring with a new one from the TBI rebuild kit. Reinstalled the TPS and turned on the smoker again. No smoke from the TPS now.

I don't see any smoke from anywhere else on the intake except the opposite side of the throttle body. There is smoke coming out from the spring on the throttle cable side of the throttle body. Basically the opposite side of the rod the TPS is connected to. There was nothing in the instructions with the TBI rebuild kit that said anything about anything with this rod. There were no parts left over in the rebuild kit that look as they would fit this rod; o-rings specifically but I'm not sure how/if this rod is sealed.

Has anyone had a '93 Chevy throttle body torn down as far as taking the 'butter flys' off the rod and removing it from the throttle body?

I haven't forgotten about testing the fuel pressure but I'm still looking for how to do that. Honestly, I haven't spent much time researching it and plan on doing that tonight.

Also, with the confusion about the block and heads, I pulled a valve cover to get the head casting numbers. Here is what I have found, for what it's worth...

Block casting number: 10243878.
When I ask the google about this casting the results I get are from a '96 - '97 Vortec 5.0L (305CI). That agrees with the additional casting details I found that show GM 5.0LG SGI

Head casting number: 14014416.
Again, google tells me that this casting is from '80 - '86 305 1.84/1.5 valves, 58cc chamber.