87 TBI Suburban bog / acceleration problem
 

I need some help with a problem that despite my best efforts persists.

The vehicle: 1987 ½ 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

TOP POST

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, (Michael Vosk) wrote:

>:|I need some help with a problem that despite my best efforts persists.
>:|
>:|The vehicle: 1987 ½ 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

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

"Michael Vosk" > wrote in message om...
> I need some help with a problem that despite my best efforts persists.
>
> The vehicle: 1987 ½ 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

"Martin Riddle" > wrote in message
nk.net...
> 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

That's your solution to everything isn't it!

Doc


>
> "Michael Vosk" > wrote in message
> om...
>> I need some help with a problem that despite my best efforts persists.
>>
>> The vehicle: 1987 ½ 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
>
>

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.
"Michael Vosk" > wrote in message
om...
> I need some help with a problem that despite my best efforts persists.
>
> The vehicle: 1987 ½ 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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In this case, its a sugestion, not a solution. Besides no one here could diagnose my problem.

Cheers

""Doc"" > wrote in message ...
>
> "Martin Riddle" > wrote in message
> nk.net...
> > 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
>
> That's your solution to everything isn't it!
>
> Doc
>
>
> >
> > "Michael Vosk" > wrote in message
> > om...
> >> I need some help with a problem that despite my best efforts persists.
> >>
> >> The vehicle: 1987 ½ 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
> >
> >
>
>

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

Bret Chase > wrote in message >. ..
> TOP POST
>
> 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
>
>
>
>
>
>

"Michael Vosk" > wrote in message
om...
> 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
>

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

"Hairy" > wrote in message
...
>
> "Michael Vosk" > wrote in message
> om...
>> 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
>>
>
> 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

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

>
>