Got a REAL stumper for the experts

[potenza]

Reckon that ground for lockup solenoid would cause the idle surge too? Or the lean condition?

And yeah this truck has no cats, straight pipes and glass packs, lol

not likely, sounds like multple problems, unhook your exhaust and see how it runs

 

[FbodTrek]

Oh yeah, compression tested great, as well as leakdown.
PCV is fresh, and Throttle body has been removed and cleaned.

 

[ShawnZR-1]

Ok, going back to the O2 sensor then. If it's reading rich, it'll lean the mixture out causing low power, drivability issues, etc. The fact that it runs OK in open loop and with the sensor disconnected seems like good indicators to me.

 

[FbodTrek]

But yeah, if it was a backpressure problem, i'd see it with the vaccum test.

 

[FbodTrek]

Ok, going back to the O2 sensor then. If it's reading rich, it'll lean the mixture out causing low power, drivability issues, etc. The fact that it runs OK in open loop and with the sensor disconnected seems like good indicators to me.

I would think the same, but when these cars see load or WOT, they go into open loop anyway, and the lean condition persists, which robs it of power.

 

[ne ga pappy]

I have seen the knock sensor do this

 

[ShawnZR-1]

Are you able to read the PW on the injectors? Does it change with throttle position?

Can you read the TPS values that the computer is seeing? I know you checked the TPS voltage but what is the computer interpreting it as?

 

[Constitution Hour]

Reckon that ground for lockup solenoid would cause the idle surge too? Or the lean condition?

And yeah this truck has no cats, straight pipes and glass packs, lol

NO the ground issue would affect it in gear while driving. What is your spark KV? = Coil output
I have seen all kinds of issues on these old trucks over the years, distributor pick up coil is another issue. Find the Tan wire w/white stripe (I think) on the firewall single wire with an inline connector, unplug the wire (that will put the system into open loop base timing) how does it respond.
Don't forget to check the throttle body vacuum fittings for being clogged with carbon, do you have good vacuum to the MAP sensor?
Does propane enrichment stablize the idle?
Check the throttle shaft where it goes into the body, they wear and can cause vacuum leaks large enought o lean out. I used to have a kit to install bushings in them.

 

[jdm333]

Do these systems use an idle air control motor? If is acting erratic I can see that causing an issue with during idle. It could act like a transient vacuum leak which is what this sounds like to me. Also, assuming vacuum brake boost try plugging the line going to your booster as you could have a leaky diaphragm. Of course be really careful driving like that if you do.

 

[FbodTrek]

Are you able to read the PW on the injectors? Does it change with throttle position?

Can you read the TPS values that the computer is seeing? I know you checked the TPS voltage but what is the computer interpreting it as?

I haven't read the TPS values AT the PCM harness yet, but the feedback signal is normal, ground and power are normal TO the ECU with TPS unplugged.

Coil output is "nice and hot", i have no HV tester, but with a gap tester is blue and hot. I figure if it were ignition I'd see a rich condition on the plaugs, not 8 bright white plugs with heat marks in normal range on the ground strap.