More TBI weirdness

[xs-style]

I've been driving this k5 (87 TBI) a couple months now. A week or so ago on the way home from work, it felt like it started running a little rough and the service engine light pops on. I pulled the codes when I got home. Code 32, egr. Next day I go out to see if I can figure it out, no service engine light and the trucks running fine. As such, I didn't worry anymore about it. But last night I had the same deal happen, a little bit of running rough and the service engine light. This time I got codes 33,34, and 42. So two map sensor codes and something to do with the electronic spark timing. Figured I'd check it out this morning since it was raining last night. Now today I've got the same situation as before. No check engine light and the trucks running fine. It kinda makes me think computer... But ya never know. Any ideas?

[SunSoaked]

I just went thru a similar situation with my Nissan truck. Do you ever smell sulphur? Mine turned out to be a bad converter. I was getting misfire and egr codes.

[xs-style]

That would make sense, but mine doesn't have a converter anymore.

[andyh1956]

If your truck still has EGR if it sticks open the manifold vacuum will fall & when the engine goes to idle the MAP will see out of parameter condition & set a code.
The spark timing code is set because the low MAP makes the ECM think you're going up a big hill at wide throttle & it tries to adjust the spark for it. But the engine is idling & so now the rest of the parameters it needs- Engine RPM, TPS, VSS don't match the low MAP & so the ECM just gives up & sets the SES light.
We went through this with our '88 K5 a long time ago.
Get a Vacuum Gauge & hook it to manifold Vacuum & mount it where you can see it. Watch as you're driving normally & you can have a value to compare to when the engine goes haywire.
Oh yeah if you aint already done it, get all those grounds on the front of the intake onto fresh wire & fasten them to the stud the neg batt cable fastens them to.

[cal30_sniper]

Welcome to why I eventually ditched TBI for a carb swap on my old '90 burb. This issue, coupled with another EGR induced stumble at steady road speeds, and about the 3rd AC Delco ignition module that fried and left me stranded was all I could take from the old TBI. Perfect excuse to dive into a heads/cam swap while you're at it. A quadrajet, Vortec heads and a mild cam do wonders for an old TBI 350.

[andyh1956]

Originally Posted by cal30_sniper

Welcome to why I eventually ditched TBI for a carb swap on my old '90 burb. This issue, coupled with another EGR induced stumble at steady road speeds, and about the 3rd AC Delco ignition module that fried and left me stranded was all I could take from the old TBI. Perfect excuse to dive into a heads/cam swap while you're at it. A quadrajet, Vortec heads and a mild cam do wonders for an old TBI 350.

Don't forget them Flat Top Pistons!

[xs-style]

Personally on this one if it were to keep giving me fits, I'd do an ls swap of some variety.

[SunSoaked]

Originally Posted by xs-style

Personally on this one if it were to keep giving me fits, I'd do an ls swap of some variety.

Me too......if I had a $ tree.

[Damien]

I think the EGR valve is a good start. I have found that almost anything will set an EGR code on a TBI engine. My '92 K1500 was giving me drive-ability issues last fall after swapping the engine and I checked nearly every sensor and the ignition swapping the parts with others that I have. One morning was especially bad making me think fuel pump. The truck was running on 7 psi.

If it were me, I would pull a vacuum on the EGR valve to make sure it is opening. If it is pulling the EGR valve off to clean up the valve may be the next step. If this checks out or does not change anything I would check the fuel pressure. I believe the spec is 11-15 psi for the TBI.

[kwmech]

I had a vehicle one time with a similar issue. It turned out to be the egr passage way. The passage way was loaded up with carbon and small pieces were flaking off and getting lodged intermittently between the pintle and the seat creating a small vacuum leak. Pulled the intake, scrubbed it out...done

[xs-style]

This thing has given me fits with the fuel pump before too. To the point I have a fuel pressure gauge mounted under the hood lol it seems to have a consistent 12-15 psi depending on gear and speed.

It hasn't had an issue in a day or two now. Reading the responses here and thinking about them, I am more inclined to think egr. If it happens again I'll likely swap for a delco. The valve and solenoid are newish (like 3-4 months), so it would be just a swap plus like 20 bucks on my end. The only thing that concerns me is kw's point. It could be a passageway getting blocked some. I cleaned out what I could see when I changed the egr, but there's always some ya can't see.

[xs-style]

Well after a few days of nothing, it's giving me 32,32, and 42 again. It's gotta be that egr.

Two things I find odd.. 1) it only does it when I'm coming home from work. 2) if I let it sit, the ses light will go out without me clearing it. Last two times, is sat overnight and was out the next morning. This time since it happened early, I'm gonna give it an hour or two and see if it's out.

[xs-style]

After about 5 hours ( forgot about it lol) I crunk it back up. No light. Ghost in the machine much?