Hey Guys I Need Help Quick

[Nick88]

Hey im new here, i have a 1988 K5 Blazer tbi (i know not gmt400 but you guys know a lot about tbi) Ive been having this issue where the truck will run super rich causing it to be very sluggish and guzzle gas. There is no smoke out the tailpipe but i went from averaging over 15 down to getting under 5mpg. Ive replaced the o2, cts and connector, map connector, iac and connector, tps connector and tested tps to verify is correct, rebuild throttle body, new fuel pump reg. and filter, new air cleaner, cleaned both grounds on top of manifold, new egr, almost everything. The truck also has developed a rough high idle and jumps from 700-800rpm then drops to jumping 600-700rpm. Please help Im lost here.

 

[WICruiser-97]

Did you replace the ECM temp sensor or the guage sensor (they are different ones)? It sounds like it is stuck in cold start enriched condition.

 

[Nick88]

Did you replace the ECM temp sensor or the guage sensor (they are different ones)? It sounds like it is stuck in cold start enriched condition.

I replaced the ECM temp sensor, AcDelco replacement, ohms are spot on and brand new connector. The problem I should have mentioned starts after it warms up, it actually runs better before closed loop, it has a new Bosch o2 sensor with only like 4k miles on the sensor

 

[Scooterwrench]

Injector stuck open or possibly tore an o-ring when rebuilding TB.
Have you checked fuel pressure?

 

[Nick88]

Injector stuck open or possibly tore an o-ring when rebuilding TB.
Have you checked fuel pressure?

Fuel pressure is right in between 11 and 12 psi, the injector has a nice spray cone and there is no leaks from the top of pod, how should I test if injector is stuck open, I heard something about the injector spraying with key on and engine off, but I do not have that. Although I can’t see the fuel coming out of injector I can see it hitting the throttle plates and running down, not sure if that means anything.

 

[Erik the Awful]

The problem I should have mentioned starts after it warms up, it actually runs better before closed loop

I'd suspect a vacuum leak. When in closed loop the enriched mixture covers up the leak. Once it goes into open loop the mixture isn't as rich and the vacuum leak causes it to run too lean and misfire. It takes more throttle to accelerate, and the unburned fuel from the lean misfire goes out the tailpipe without contributing.

 

[Nick88]

I'd suspect a vacuum leak. When in closed loop the enriched mixture covers up the leak. Once it goes into open loop the mixture isn't as rich and the vacuum leak causes it to run too lean and misfire. It takes more throttle to accelerate, and the unburned fuel from the lean misfire goes out the tailpipe without contributing.

I tried checking for vacuum leak with carb cleaner in all the regular spots, TBI base gasket, all vacuum hoses, around intake manifold, but none seemed to make a difference, I think it might be one of three things but I’m not sure. I’m thinking either the knock sensor Since it’s original maybe screwing up timing, the grounds on the manifold I cleaned and shortly after I noticed the high idle- maybe I should replace the eye connectors???, and maybe the map is bad but I doubt it because I swapped in a replacement map from another blazer and it ran the same.

 

[Erik the Awful]

Check the throttle shaft for leaks.

Try unplugging the knock sensor.

Replace the eye connectors and make sure the wires are clean and tight.

 

[evilunclegrimace]

At this point all you are doing is guessing,hook a scan tool to the truck and find out what live data is telling you.

 

[Nick88]

Check the throttle shaft for leaks.

Try unplugging the knock sensor.

Replace the eye connectors and make sure the wires are clean and tight.

Should I check throttle shafts with carb cleaner similar to a vacuum leak?