87 TBI Suburban bog / acceleration problem

I need some help with a problem that despite my best efforts persists.
The vehicle: 1987 ฝ ton 4wd Suburban with 350 TBI, AT, 67K original miles, all stock
The problem: on starting from a dead stop, there is an intermittent severe bog until mid RPMs then acceleration is as normal or near normal. Sometimes this bog is only on starting; sometimes it is at the low end of each gear. When the problem is occurring, acceleration during low RPMs is the same for full pedal, or light pedal. As I said, the problem is intermittent. When things are working, acceleration is great throughout and smooth and proportional to pedal travel. The problem seems to be more prevalent when hot, but does happen also when dead cold. No error codes are stored. MPG is not noticeably affected (bad as it ever was). The problem is not noticeable on the freeway. It seems to happen only on starting from a stop, and more often after sitting idling for a significant time (more than a minute or so).
What I have done: Changed 02, TPS, MAP, TBI gaskets, plugs, wires, cap, rotor, fuel filter. Checked timing (0 deg with wire disconnected), fuel pressure (13 psi), all hoses checked for vacuum leaks. EGR operation checked (by shop). Injector cleaner run though. Changed gas stations over last 5 tanks. I have tried disconnecting the 02 sensor but the symptoms are the same (I do get an error code then though). Same for the EGR system.
Other: I am not sure how the timing is supposed to work on this, but here is how it does work. With the test wire connected, timing appears to be advanced about 10 degrees at idle. When the throttle is bumped, the timing goes back to zero and climbs with RPM. With the test wire disconnected, the timing is at zero but the idle hunts a bit (idle is steady with the test wire connected).
Thanks for any help you can provide. At this point, I would dump the TBI and go carb, but the under the hoods in NV eliminate that option.
Disclaimer: I know some will note the "money I saved" in replacing all the sensors etc over taking it to a shop. I did take it to one shop here where they declared the fuel filter to be the culprit. This was changed by the shop and victory was declared. Of course, when I insisted on a test drive to verify the problem was solved, the problem remained. Their next suggestion was to change the harmonic balancer and the timing belt (timing belt on a 350?). I considered continuing to dump my wallet, but instead opted to pay them the $170 I owed them for the filter change and left. Since then, I have heard nothing but horror stories about mechanics here in Vegas. I was lucky to leave having spent that little. Many of my office mates have spent thousands with no results. I simply don't have the time or money to visit several shops on the slim chance of finding an honest mechanic here. So, I will be fixing this myself….unless there is a Vegas mechanic out there willing to let me pay only for service that actually fixes the problem.
Regards, Mike
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your fuel pressure regulator is probably leaking. when they leak they dribble gas into the engine and cause it to load up, causing your bog. you wouldn't happen to have to crack the throttle to get it to start do you?
hth, Bret
On 28 Sep 2004 13:55:37 -0700, snipped-for-privacy@juno.com (Michael Vosk) wrote:

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This problem started about a month ago. I have not really noticed a difference in starting it up, but I haven't really paid much attention to it either. Now that I think about it, I usually do crack the throttle a bit (but not much)and that is probably out of habit from carbs. I will get a rebuild kit and see if that helps. The pressure was at 13 psi, but I suppose it could be leaking.
Thanks for your response. Any other thoughts out there?
MV

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I could be wrong, but I think you would definitely have hard starting problems if it was the fuel pressure regulator. I think the suggestion by David and Lynn Shepherd is worth looking into. H
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Sometimes, sometimes not with the hard starts. As the TBI's are only cooking 9-13 psi to start with, this bleeds off pretty quick when the truck is shut off, and if it sits overnight most of the fuel dumped in there will have evaporated anyways by the time he cranks it in the morning. A good test would be key on, 3 second pause, key off (repeat 10 times or so) to get the fuel pump pressuring up repeatedly and allowing the FPR to dump lots o' fuel into the motor. Then try and start it.
I do agree with you that D and L Shepherd's suggestion is worth looking into as well.
Doc

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Another possibility, beyond the EGR and FP, is the ignition pick-up coil. I had the same symptoms, except when cold. The pickup coil had some green corosion on its copper windings that affected its operation.
Cheers

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In this case, its a sugestion, not a solution. Besides no one here could diagnose my problem.
Cheers

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This could a torque convertor problem, a failed overrun clutch on the stator, when it is doing it have someone who knows what to look for stall test the trans ( should be a trans shop), if the stall rpms are low, which would account for it being dead on accel from a dead stop. This can be tough to differentiate from a general power loss from the engine.

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I had the same problem in a '89 blazer. I tore the engine down to put a cam and carb on it just to find a very loose timing chain. I wasted a lot of money on cam, lifters, sensors, intake and all it was is a loose timeing chain.
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I had the same problem in a '89 blazer. I tore the engine down to put a cam and carb on it just to find a very loose timing chain. I wasted a lot of money on cam, lifters, sensors, intake and all it was is a loose timeing chain.
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Thanks to all who posted with suggestions. The good news is, you guys know your stuff. The bad news is, the tranny was the problem. The shop confirms the torque converter is toast. The really bad news though was all the metal shavings in the pan (guess I should have quit driving it sooner).
Thanks again, I doubt I would have found the problem before it left me stranded without all your help.
MV
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