92 5.7 TBI complete loss of power under load

amizzly · January 26, 2015

Hey everyone.

I posted in this site around a year ago while having issues with my truck. Now I've gotten most issues handled that I was having in the past, and no more check engine light. However, I'm having a new problem that everyone I speak to seems to be completely dumbfounded by. I thought I'd broaden my "support group" by asking you all again.

MANUAL TRANSMISSION!!!!

The problem: my truck seems to be slightly underpowered, especially within the first two minutes or so of driving when its very cold outside. This I can live with. What I can't live with is that I cannot put it under any sort of load, ever, or it completely halts power output.

What I mean: I'll be driving down the road, and let's say I'm going 25 and a decent sized hill is upcoming. If I don't feather the gas or shift into 2nd (putting me at 3k Rpm) the engine stops running while in gear. If I completely let off the gas pedal, it cuts back in and runs normally. If I'm going down the highway 65mph in 5th gear, if there's any sort of positive incline, I must pump the gas very carefully or the engine ceases power output; once again if I let the gas pedal out all the way, the engine starts running again completely normal. I live in the country, and as such there's tons of old roads to test on. If I don't let of the gas pedal in this situation, or if I give it more gas, the truck will slowly decelerate, and around like 5mph it will shake violently like if you were to accidentally start in 4th instead of 2nd, and then the truck stops.

No one I know can give me any definitive answer, including three master technicians within my family tree. Has anyone every had any issue like this? I work at a shop and have access to direct hit. I searched my issue there and could find no related posts.

I should probably add that the truck starts instantly, never misses at idle, and never stalls or has any other problem whatsoever other than what is mentioned.

Thanks for reading

Squirrely · January 27, 2015

The three things to check; fuel, spark, air. Do you have them all?

amizzly · January 27, 2015

I know I have no vacuum leaks, because I've sprayed everywhere and no effect, plus my idle is about 750 rpm, which I believe is correct. not sure how I'd check fuel or spark during these situations as the only time my issue occurs is while driving. I do however know that I have no wires, etc. arcing and that my timing is set properly (0° with timing light). I also know that my fuel pressure is around 13psi, which I believe is correct. I've actually started to believe that I may have an issue with my ecm or a plugged catalytic converter maybe? What are your thoughts?

What I'm perplexed by is that I have no issues taking off, idling, or starting. It does those three things like a brand new vehicle. The only time the truck really shows any issue is cruising/accelerating under a load.

Duelin · January 27, 2015

Have you tried disconnecting the EGR valve and driving it and see what happens?

00Silverado4x4 · January 27, 2015

I am probably wrong but I thought fuel pressure was higher then that. 13 psi seems awfully low for a fuel injected engine.

Duelin · January 27, 2015

For that TBI system the pressure should be 9-13 psi

Squirrely · January 27, 2015

Have you tried disconnecting the EGR valve and driving it and see what happens?

I would also try this. Block it off entirely if you can.

amizzly · February 1, 2015

Well plugging up the egr didn't help. I'm really starting to believe my problems are the result of a plugged up catalytic converter. Thoughts?

Duelin · February 2, 2015

If you think it is the converter remove the O2 sensor (less back pressure) and drive it and see if there is any improvement.

1997SierraSLT · February 3, 2015

catalytic converter clogged up perhaps? Had this issue with an 87' El Camino I owned many years ago. Put a new one on and it ran like a brand new car....err... truck....err....

Bswindle95 · March 13, 2020

I know this is a five year old post but I'm having the Exact same problem to a freaking t and right now the only place this truck is driving me is to drink... did you anyone ever figure out what the issue was this guy was having? My truck is doing the exact same thing and I'm running out of money to throw at it...