fuel problems?

[BroncoDan]

I have been troubleshooting a problem with my 89 BII. It's a 2.9L auto 4WD... the vehicle drives fine from 0-45mph which is where i do most of my driving... however when i get over 45mph, really about 47mph i have noticed that the vehicle shakes when it drops into overdrive... if i let up on the gas it stops or if i accelerate it will stumble for a second and then it downshifts and smooths out... everything i have done to this point has helped but the symptoms are still present albeit much better than before... here is a list of what i have done:

1. pulled codes... only thing i got was a code for high idle one time and it has not come back since...

2. replaced every vaccuum hose i could find... the previous owner literally tried fixing them with electrical tape

3. spark plugs and wires... used a wire tester to make sure i had good spark on all wires...

4. seafoamed with oil change and dropped some in the fuel tank too... had never used seafoam before but it made me a believer...

5. replaced fuel filter and found one more vaccuum hose that goes from the firewall mounted canister back to the intake... this has given the best results so far... my gas mileage has improved tremendously and the symptoms are not as noticeable

6. tested fuel pressure... 29psi Chilton manual says it should be 35-45psi so cheapest thing first... replaced fuel pressure regulator... this actually made the problem more noticeable again...

at this point i am thinking fuel pump... this vehicle had sat for 5 years before the previous owner got it and i am wondering if he just dumped gas in it and cranked it given that the fuel filter made such a difference...

i was also thinking transmission but it really feels more like the motor missing than a tranny problem but i am going to do a fluid and filter change this weekend since it is such an old vehicle....

anybody have any other suggestions or ideas for troubleshooting? also if i do replace the fuel pump will this pump support a 302? i am about to start working on a 302 setup and i figure if i am going to buy new parts for the BII i want to make sure i am not throwing money into something that i am just going to have to replace soon...

oh and one more thing... if i put the BII in drive instead of overdrive the problem still shows up once i hit my cruising speed just a lot less noticeable

 

[IMenriched]

Might be the hanger bearing on the driveshaft???

 

[BroncoDan]

several people have said driveshaft so how would i check that... i've tried moving the shaft and there doesn't appear to be any movement any direction... wouldn't a driveshaft problem be apparent at a specific rpm range?

 

[Tedybear]

Sounds like "Torque Converter Chuggle"

Problem GM used to have in the worst way. Hit about 45mphish...Maintaining that speed (no hitting the gas or letting off on it) The torque converter clutch kicks in. Makes it a direct connection inside the torque converter. The slight increase in load brings the speed down slightly...so the TCC disengages.....decrease load...speed goes up...TCC engages again---wash and repeat--

When the TCC kicks on? It can in some cases feel like a "Shift" of the transmission. If you increase speed a few MPH over that point and it clears up totally? I'd almost suspect that could be it.

Drive shaft vibs are not always dependent on the engines RPM. But are dependent on the speed you are going. I see you're in the same truck as ours. If it's still got the CV joint type? (aka...the Tulip bulb type).. It's a pain in the rear, as ours didn't show any outward signs of failing...but we had a metal "crunching" sound when going from 5mph-20mph...sounded exactly like a bad CV joint on a front wheel drive car.

edit: It will sound or make bad vibs worse when doing a harder accel. The increased torque on the drive shaft makes it bind up stiffer.

S-

 

[BroncoDan]

Sounds like "Torque Converter Chuggle"

Problem GM used to have in the worst way. Hit about 45mphish...Maintaining that speed (no hitting the gas or letting off on it) The torque converter clutch kicks in. Makes it a direct connection inside the torque converter. The slight increase in load brings the speed down slightly...so the TCC disengages.....decrease load...speed goes up...TCC engages again---wash and repeat--

When the TCC kicks on? It can in some cases feel like a "Shift" of the transmission. If you increase speed a few MPH over that point and it clears up totally? I'd almost suspect that could be it.

Drive shaft vibs are not always dependent on the engines RPM. But are dependent on the speed you are going. I see you're in the same truck as ours. If it's still got the CV joint type? (aka...the Tulip bulb type).. It's a pain in the rear, as ours didn't show any outward signs of failing...but we had a metal "crunching" sound when going from 5mph-20mph...sounded exactly like a bad CV joint on a front wheel drive car.

edit: It will sound or make bad vibs worse when doing a harder accel. The increased torque on the drive shaft makes it bind up stiffer.

S-

Hey Tedybear thanks... that's exactly the driveshaft i have and it isn't making noise... most definitely the problem clears up on acceleration rather than gets worse which is kind of what i would expect from a driveshaft problem.. ... it only happens when the tranny drops into OD and for a second or 2 as i accelerate...

i was driving it last night and once again the problem seemed to be a lot less noticeable...

any suggestions on how to troubleshoot for TC problems? my only experience has been with 5 speed mustangs so these automatics are a completely new creature to me... does the transmission have any kind of vaccuum lines? i know it has a vent hose... i wonder if with all the dry-rotted hoses if i'm just not dealing with a vaccuum problem from the tranny...

 

[whitie]

find out exactly when the problem occurs and simulate it except next time have you overdrive off. if it still shutters then its not your converter clutch.