I'm having a problem with a stock 1989 GMC Sierra 1500 - 305 engine. It has no power off the line even though I have the gas pedal right down. Sometimes it picks right up and goes from a stop. Other times it moves out slow with no power (not stumbling or missing). It goes through all 3 gears though even when it has the "no power" symptom.After I'm in3rd gear on the highway and you kick down the pedal on the highway, no problem. This problem only happens from a dead stop, and then just occasionally.

I've had several things changed but no results yet. (map sensor, main distributor shaft, fuel pump strainer, fuel pump, cat converter, muffler, electronic control unit, sending unit). My mechanic gave up and thinks it might be a partially locked up torque converter. Trany shops don't think so though. Trany guys say this 400 hyrdramatic trany does not have electric torque control, it's mechanic/hydraulic. I checked the governor and it's ok. Problem all started when I had the trany fluid and filter changed (may be a co-incidence). The gm service center says my truck would not have a TV cable, it has vacuum control to the trany. Any ideas much appreciated.

 

OK i think you answered your own question, as a former mechanic i always asked the question you have been having this since when? usually when you change something and get a new problem you cause it yourself. if you just changed your fluid and filter i would #1 check fluid level, #2 check the filter, sometime they r not seated proprly or loose, this can cause a lack or fluid and or pressure. As i was reading your post the converter stuck out the most to me, i would say that its either that or a bang inside the trand that isnot relasing all the way. i would check with another mechanic.

 

One other thing that I didn't mention before is thatthe truckintermittentlyhas ahigh speed vibration (when stopped). It will go away when I put it in neutral or park. Sometimes at a stop it does not vibrate and sometimes it does.

 

Thanks Vegas. I've opened the pan on the trany 2 weeks ago to check the condition of the fluid (trany fluid change was 12 weeks ago). It had a bit of black sludge on the bottom of the pan ( a thumb wipe full) anda fewsmall bits of metal (not much). I filled it back up with new fluid to the proper level. Never really checked the filter to see if it was seated. I also pulled the governor out (suggestion for a tranny mechanic) and checked it. It was ok.

What would happen if the filter isn't seated?

 

if not seated properly the obvious is your fluid will not get cleaned, but you can have either too little or too much fluid running through it. it can also mess up the pressure in the trans, which usually causes irratic shifting, a stuck or loose converter, but that black sludge does not sound good if the fluid was changed 3 months prior. some trans shops have what is know as a power flush, which is the ulltimate in cleaning trans fluid, maybe something you would wanna try, or now that i think of it, if the problem happened after you changed the fluid its possible that the trans is toast, if we had a customer who had like 100k and never did a tranny service we wouldnt do it cause the new fluid is too clean (i know sounds ridiculious) but after about 2 weeks the trans would take a dump. there is a lucas oil additive for the trans... maybe something like that would do the trick, but i think its your converter and or trans.... sorry dude

 

Yes, I've heard if you have a trany that is slipping you should not change the fluid because that would make it worse. I bought the truck brand new. It's now got 362,000 kilometers on it. From 220,000 km to 310,000 km this trany used to pull during the summer my boat. It weighed 9500 lb. It never had a problem with that. Hard work on her though. I sold the boat and the truck doesn't get used a lot. I have a small car for going to work. When I pulled the boat I'd have the trany fluid changed once or twice a season. But since I quit pulling the boat, I haven't had the trany fluid changed till just 3 months ago (when problem started). I'd lean toward thinking it's the trany, but the darn trany shops say it's not the trany. The one trany guy drove it, said it's not the trany because when he held the brake pedal down (truck didn't move) and gave it some gas, the engine went flat (didn't rev up). He said that's an engine problem.

 

is that tbi?

 

Sorry, what does tbi mean?

 

yes an 89 is tbi. and also it should be a 700r4 tranny and not a 400 hydromatic. those are super old. and it will have a tv cable but not electronic controls to it.

 

This 89 Sierra is a 3 speed and is confirmed to be a 400 hydromatic transmission. Not sure what tbi lingo means but if it's "throttle body injection", then yes that's what it has.

Sympton added: When I step on the brake and push on the gas(when the problem is occurring), theengine will go flat (no acceleration or power). If I shift the tranny to "Park" and rev the gas pedal, then engine revs up with no missing or stumblingand sounds fine. Put it back in "Drive", push the gas pedal and the engine goes flat again.

This happens only when the intermittent symptom is occurring. When it is not, then if I step on the brake and rev the engine while in "Drive", then the engine revs and the truck lurchs against the brake. Lots of power. But when the symptom is occurring it goes flat.

I think there is something wrong with the tranny. What do you think?