'97 GMC 350 Engine Performance

My GMC suddenly started cutting out under load. I've noticed it
occasionally missing in 3rd gear and OD so far and tried to get it to
do it in 2nd yesterday afternoon but never could. Doesn't idle rough
(had it tuned up about 5k miles ago at the dealer) and it's doing this
around 2300 RPMs, generally on a slight uphill grade.

It ran so smooth in 2nd yesterday that I'm wondering what 'emissions'
type devices might be causing something like this. (noted the missing
BTW as something that almost feels like a sharp wind hitting the
vehicle with a momentary dip in the tack reading). Any ideas folks?

On Nov 4, 1:54 pm, cover > wrote:
> My GMC suddenly started cutting out under load. I've noticed it
> occasionally missing in 3rd gear and OD so far and tried to get it to
> do it in 2nd yesterday afternoon but never could. Doesn't idle rough
> (had it tuned up about 5k miles ago at the dealer) and it's doing this
> around 2300 RPMs, generally on a slight uphill grade.
>
> It ran so smooth in 2nd yesterday that I'm wondering what 'emissions'
> type devices might be causing something like this. (noted the missing
> BTW as something that almost feels like a sharp wind hitting the
> vehicle with a momentary dip in the tack reading). Any ideas folks?

Wires.
Fuel Filter.
Don't jump to "emissions type devices" or anything else until you
cover the basics.

dahpater wrote:
> On Nov 4, 1:54 pm, cover > wrote:
>> My GMC suddenly started cutting out under load. I've noticed it
>> occasionally missing in 3rd gear and OD so far and tried to get it to
>> do it in 2nd yesterday afternoon but never could. Doesn't idle rough
>> (had it tuned up about 5k miles ago at the dealer) and it's doing this
>> around 2300 RPMs, generally on a slight uphill grade.
>>
>> It ran so smooth in 2nd yesterday that I'm wondering what 'emissions'
>> type devices might be causing something like this. (noted the missing
>> BTW as something that almost feels like a sharp wind hitting the
>> vehicle with a momentary dip in the tack reading). Any ideas folks?
>
> Wires.
> Fuel Filter.
> Don't jump to "emissions type devices" or anything else until you
> cover the basics.
>
I had a similar situation. Turned out I was losing fuel pressure inside
the fuel tank. At less than full load, all was well. Max load caused a
stumble. Isolation hose between pump & delivery tube leaked by hose clamp.

I agree on the fuel pressu

But, on the transmission slipping from second to third. If it's a 4L60E or
4L65E, there is an issue with the pressure control valve for the lock up
torque converter.
I would have this checked, before it costs you a total rebuild. With lots of
hard parts.

Now you can just have the valve body machined, or use a shift kit, with an
insert type valve.

RK
"syoung" > wrote in message
...
> dahpater wrote:
>> On Nov 4, 1:54 pm, cover > wrote:
>>> My GMC suddenly started cutting out under load. I've noticed it
>>> occasionally missing in 3rd gear and OD so far and tried to get it to
>>> do it in 2nd yesterday afternoon but never could. Doesn't idle rough
>>> (had it tuned up about 5k miles ago at the dealer) and it's doing this
>>> around 2300 RPMs, generally on a slight uphill grade.
>>>
>>> It ran so smooth in 2nd yesterday that I'm wondering what 'emissions'
>>> type devices might be causing something like this. (noted the missing
>>> BTW as something that almost feels like a sharp wind hitting the
>>> vehicle with a momentary dip in the tack reading). Any ideas folks?
>>
>> Wires.
>> Fuel Filter.
>> Don't jump to "emissions type devices" or anything else until you
>> cover the basics.
>>
> I had a similar situation. Turned out I was losing fuel pressure inside
> the fuel tank. At less than full load, all was well. Max load caused a
> stumble. Isolation hose between pump & delivery tube leaked by hose clamp.

cover wrote: (1997 GMC 350 Engine Performance)

My GMC is cutting out under load. It occasionally
misses in 3rd gear and OD but not in 2nd. It does
this at around 2300 RPM, generally on a slight uphill
grade. When it misses it feels like a sharp wind
hit the vehicle with a momentary dip in the tach
reading). It idles smoothly (dealer tuneup 5k miles
ago). Any ideas?
________________________________________

Wires. Fuel Filter.

Don't jump to "emissions type devices" or anything
else until you cover the basics. dahpater
________________________________________

I had a similar situation. It turned out that I was
losing fuel pressure inside the fuel tank. At less
than full load, all was well. Max load caused a
stumble. Isolation hose between pump & delivery
tube leaked by hose clamp. "syoung"
_________________________________________

It's probably not the fuel delivery system because it
only happens at part throttle.

It's probably not the high voltage system (wires, coil,
distrib, plugs), as it doesn't happen at full throttle.

Some other possible causes:

-- Sticking IAC
-- Intermittent Igniton Module failure.
-- Trans downshifting late.
-- TCC engaging too soon under load.

Trans and TCC errors could result from erroneous load
sensors such as manifold vacuum or throttle position.

Good luck.

Rodan.

sounds like the fuel pump is not working 100%. What are your fuel
pressure test readings?

On Nov 4, 7:09 pm, "Rodan" > wrote:
> cover wrote: (1997 GMC 350 Engine Performance)

>It's probably not the fuel delivery system because it
> only happens at part throttle.
>
> It's probably not the high voltage system (wires, coil,
> distrib, plugs), as it doesn't happen at full throttle.

Yes, fuel, wires will cause this problem!


> Some other possible causes:
>
> -- Sticking IAC
> -- Intermittent Igniton Module failure.
> -- Trans downshifting late.
> -- TCC engaging too soon under load.
> Trans and TCC errors could result from erroneous load
> sensors such as manifold vacuum or throttle position.

He didn't say he has transmission problems!


>
> Good luck.
>
> Rodan.

On Nov 4, 7:00 pm, "Refinish King" > wrote:
> I agree on the fuel pressu
>
> But, on the transmission slipping from second to third. If it's a 4L60E or
> 4L65E, there is an issue with the pressure control valve for the lock up
> torque converter.
> I would have this checked, before it costs you a total rebuild. With lots of
> hard parts.
>
> Now you can just have the valve body machined, or use a shift kit, with an
> insert type valve.


No where in his post does he mention "transmission" problems! There is
no mention of "slipping from second to third". He is discribing a
"running" problem.

<dahpater yahoo.com> wrote:

He didn't say he has transmission problems!
_____________________________________________

<dahpater yahoo.com> wrote:

Nowhere in his post does he mention "transmission"
problems! There is no mention of "slipping from
second to third". He is describing a "running" problem.
_____________________________________________


Thank you for your helpful contributions.

Rodan.