1993 Chevy K3500 - Rough idle and stall

[PlayingWithTBI]

There is smoke coming out from the spring on the throttle cable side of the throttle body.

Your "butter flys" blade shaft bushings are probably worn out, need to replace them, or have it rebuilt by someone like SPR Perfomance or R.V.Morse Machining.

I haven't forgotten about testing the fuel pressure but I'm still looking for how to do that. Honestly

Try 62-FP, 62-PG, and might as well 62-FR

http://www.rvmorsemachine.com/product.htm

Here's what mine looks like (I'm running a little higher pressure than stock, yours should be ~11-13psi

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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.

You really have a unique combination, good luck and enjoy!

 

[Schurkey]

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?

Your "butter flys" blade shaft bushings are probably worn out, need to replace them, or have it rebuilt by someone like SPR Perfomance or R.V.Morse Machining.

The FIRST thing you need to know about the screws holding the throttle blades, is that they're staked on the underside. DO NOT TRY to remove them until AFTER you grind the "bottom" of the screw even with the throttle shaft to remove the staked portion. You WILL break the screws if you try to just spin them out without grinding the bottom first.

My buddy the machinst uses thin-wall valve guides to re-bush the throttle shaft bores. He finds a valve guide of the proper ID, cuts it to length, and presses them into the bored-out holes using a threadlocking compound to retain them. Dress the throttle shaft so there's no burrs that would damage the new bushings when the shaft is inserted.

The trick in this is to get the existing worn holes bored oversize AND IN-LINE, concentric with where they were when new.

Any moron can poke a drill bit through each of the holes, but that may get the hole out of position, or not in-line with the hole on the other side.

HOWEVER, I'd be checking for actual movement of the throttle shaft to try to judge "how worn" the hole is. My best guess is that you don't have enough wear to account for the rough running you have. Perhaps I'm wrong...but re-bushing the throttle shaft would be about the LAST thing I'd do, unless the throttle shaft was flopping around in the throttle body.

Have you considered a cylinder-balance test to trace down which cylinder is misfiring? IF (big IF) the misfire isn't random--spread among all the cylinders haphazardly--knowing which cylinder(s) are the problem children would go a long way toward diagnosing the root cause.

 

[JWAZ73]

Well, friends, we have progress!

I completed the smoke testing of the intake. I completely removed the throttle body from the intake and injected smoke into just the intake to test the gasket. As it turns out, the EGR valve leaked like crazy. Replaced the EGR valve.

I reassembled the throttle body (I did not mess with the throttle shaft or blades), reinstalled it, and started the truck. Still had the idle issue.

Replaced the ignition coil. Still had the idle issue.
Replace spark plug wires. Still had the idle issue. The wires were old and stiff, probably needed to be replaced anyway.

At this point I was frustrated. We started the truck and gave it enough throttle to keep it running. Checked the fuel pattern with a timing light in the throttle body, used the scan tool to look at fuel trims and other sensors. Then, all of a sudden, it started idling normally. What!?!? I sat there for a few minutes and was pondering the actions of the day, wondering what made the difference. I'm wondering if after changing the EGR that I didn't give the computer enough time to 'think about' what had changed and make corrections. We got in the truck and went for a 45-minute drive. It ran beautifully. Stop and go, sitting and idling, we just drove it around the town. We got back home, put the tools away and my son decided it was time for some ice cream and wanted to take his truck (this one). Got in, started right up. Backed out of the driveway and it stalled. Started right back up and drove about five minutes to the ice cream shop. Several stop signs and lights and no issues. Pulled in the parking lot, stalled again. After ice cream, we got in the truck and drove home with no issues.

Silly me, I did not have the scan tool connected for any of this driving. After we got home I pulled up a recorded scan that I saved and for some reason, something told me to look at the O2 sensor more closely. I remember saying in here that the O2 sensor seemed to be bouncing around on voltage as expected. When I looked closer at the actual voltages it was never outside the range of 400 - 500 mV.

This engine is running remarkably better than last weekend. If the O2 sensor is faulty or 'lazy', could that now be contributing to this last bit?

I also discovered an exhaust leak on the passenger side of the engine. Haven't pinpointed the location yet but as we were trying to troubleshoot this afternoon we managed to make the engine run very rich and saw black smoke coming up from around the exhaust manifold. Not sure if that would contribute anything or if back pressure is applicable here...

I also still need to do the fuel pressure test. None of the parts stores near me have a loaner test kit so I'm going to have to either find someone who does, order one, or get one of those gauge assemblies @PlayingWithTBI mentioned in his last post.

The plan for tomorrow is to hook up the scan tool when cold (as cold as it will get in Phoenix in the summer) and record data, from cold to normal operating temp, and drive it more. I will pay attention to loop condition (open/closed) and what the O2 sensor is doing.

 

[Schurkey]

Progress is good. Congrats.

Yes, re-check the O2 sensor voltage and cross-counts.

 

[JWAZ73]

Well, when we took the truck out the next day we ran into additional trouble but more on that later in the post. I hooked up the scanner and went for a drive (emissions testing and motor vehicle if all goes good). I remembered to record the scan this time so I could go back and look at it. As far as the O2 sensor goes, as soon as the loop changed to closed the O2 sensor began rapidly changing voltage. The sensor was reporting voltages from 48mV on the low side to 845mV on the high side. Looking at the graph it's averaging about three cycles per second. The TunerPro mask I'm using doesn't seem to have a counter for cross-counts and I haven't been able to find where in the datastream that metric is to read it. From what I have read elsewhere online the O2 sensor should cross the midpoint (about 450mV?) about 10 times per second. If that is the case then this sensor is behaving lazily.

The new issue was that it was having a hard time starting, like the (brand new) battery was dead. We did get it home and I put it on the battery charger. The charger said it was 80% charged so I topped it off and tried to start again. Would not start. All it did was a very slow cranking motion. Took the battery out and back to where I bought it to have it tested. It tested as a good battery. Removed the starter for testing and took the alternator off as well since it seemed it wasn't keeping the battery charged. Both passed the testing.

Reinstalled the starter and alternator. Rigged up a piece of wire from old welding leads to connect the starter directly to the battery. Cranked hard and started right up. Ordered new positive and negative battery cables.

New battery cables are installed. The truck starts up quickly and now idles smoothly. The last remaining issue is that when sitting in gear with your foot on the break struggles to keep running then will stall. Here's a link to a video of it.

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Is this still a vacuum leak somewhere?

 

[Schurkey]

Is this still a vacuum leak somewhere?

Does the O2 sensor indicate a vacuum leak (lean?)
Idle speed indicate a leak (Too high)
IAC responding properly? IAC commanded to a low-idle speed position as if the engine were getting additional air it shouldn't be?

What is the commanded idle speed vs. actual idle speed?

 

[JWAZ73]

Does the O2 sensor indicate a vacuum leak (lean?)

In the recording of the driving session in the scan tool the long term fuel trim (BLM) stayed at 135 or above. This including periods of idling and driving. I believe higher numbers are lean and normal is 128. (could be wrong to feel free to correct me.)

Idle speed indicate a leak (Too high)

On a cold start it idles about between 850 and 900. The scan tool indicates the desired idle is 600.

IAC responding properly?

On a cold start, at idle, the IAC position is between 60 to 75 then works its way down to between 30 and 45. This close to the IAC table in the bin file for the truck. At 32 C (70 F) the IAC should be at 55. At 44 C (111 F) the IAC should be at 35. When driving it seems to stay around 110.

 

[PlayingWithTBI]

Ordered new positive and negative battery cables.

Also check your gounds - Battery to body, engine to frame, wires to T-stat housing, back of engine to body, etc.

In the recording of the driving session in the scan tool the long term fuel trim (BLM) stayed at 135 or above. This including periods of idling and driving. I believe higher numbers are lean and normal is 128. (could be wrong to feel free to correct me.)

Yes that's right, as @Schurkey said, you may have an intake/vacuum line leak. Or your VE (Volumetric Efficiencies) table isn't dialed in close enough for your set up, your PCM can only adjust ~10 - 15% on your INT/BLMs.

Or your fuel pressure is too low, injectors semi-plugged/undersized (you're sure you have the correct injectors for your engine), which will lean out your AFR too.

 

[JWAZ73]

@PlayingWithTBI, good point on the grounding straps. I forgot to mention this in my earlier post. When replacing the battery cables I noticed the grounding strap from the engine to the frame was completely severed. Since the body ground strap was right there I replaced both making sure they had good clean metal contact. After replacing the battery cables and the grounding straps is when I noticed the 'miss' had gone away completely. Also, the scan tool reports a running voltage of 14.04V compared to 13.4 - 13.8 with the old cables.

Or your fuel pressure is too low, injectors semi-plugged/undersized (you're sure you have the correct injectors for your engine), which will lean out your AFR too.

I did recently install new injectors appropriate to the 305 engine displacement. I also forgot to mention that I found a parts store that has a fuel pressure test kit to loan. It's about 20 miles from the house so I'll stop by and borrow it one day while I'm out and when I have the time to dig into that test.

 

[PlayingWithTBI]

Since the body ground strap was right there I replaced both making sure they had good clean metal contact. After replacing the battery cables and the grounding straps is when I noticed the 'miss' had gone away completely.

Good job!

I did recently install new injectors appropriate to the 305 engine displacement.

Were they new or reconditioned? Were they "matched" and flow tested? Big difference.

I also forgot to mention that I found a parts store that has a fuel pressure test kit to loan.

Book says 9 - 13psi, preferably 11 - 13psi. If not, get an AFPR, I have a setup from http://www.rvmorsemachine.com/product.htm

pn #s 62-FP, 62-PG, & 62-PR - make sure you use plenty of Teflon tape or it'll leak (ask me how I know lol).

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Looks like this installed - I'm running higher pressures with a bigger spring and vortec fuel pump but, you get the idea.

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