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Chris (aka-Moose)
Chris (aka-Moose), GMC Technician
Category: GMC
Satisfied Customers: 48381
Experience:  16 years of experience
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96 GMC 1500 4.3L and lately when putting in drive or reverse

Customer Question

96 GMC 1500 4.3L and lately when putting in drive or reverse when moving from a stop the truck stalls about 20% of the time and i think its getting worse. What could possibly be wrong here?
Submitted: 1 year ago.
Category: GMC
Expert:  Chris (aka-Moose) replied 1 year ago.

Welcome, I am Chris (aka-Moose)

Does it stall when selecting D or R or does it stall once you start moving?

Is the transmission oil, full, a good color and odor?

Can you keep it running with throttle applied?

----------Once you get an answer----------

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2) The more you can tell me the faster and better I can help.

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6) I am going to stay in contact with you until you respond and tell me your happy or pleased with the answer. So please reply and let me know the progress on the issue and our discussion or if more help is needed.

Thanks Chris

Customer: replied 1 year ago.
Ok so I guess it's something different and a cause is pushing the gas pedal too far down. I took it on the road and anything more then 25% full throttle and it lurches hard (rpms shoot up and down) until I take my foot off the gas. I tried duplicating it and every time I press the gas it lurches hard and about half the time it will turn the truck off and I find myself coasting.
Expert:  Chris (aka-Moose) replied 1 year ago.

Since its based on throttle pressure and position. Do you have the tools to monitor the air fuel sensor, throttle position sensor and throttle pressure during this event to see if they are acting up once you reach a set throttle position.

Customer: replied 1 year ago.

not sure. can this be done with a regular scan tool?

Expert:  Chris (aka-Moose) replied 1 year ago.

All depends on what you mean by regular. Can it monitor computer inputs or just read codes?

Customer: replied 1 year ago.

there is a data section that i can monitor %s and things like that. has like 100 items on the list

Expert:  Chris (aka-Moose) replied 1 year ago.

Great can you montor these things while driving to look for a drastic change once 25% throttle is reached. All readings should gradually increase or decrease.

Customer: replied 1 year ago.

i guess. tell me what ill be looking for because man its scary driving it.

Expert:  Chris (aka-Moose) replied 1 year ago.

You need to look at TPS and MAF/MAP readings. Fuel pressure is checked with a gauge.

Customer: replied 1 year ago.

ok ill let you know. thanks

oh, actually there was a map code but i reset it last week. po108 . would this cause the problem i am having?

Expert:  Chris (aka-Moose) replied 1 year ago.

Super

Customer: replied 1 year ago.

?

Expert:  Chris (aka-Moose) replied 1 year ago.

You typed ( ? ) Do you need something?

Customer: replied 1 year ago.
I asked a question and you said super
Expert:  Chris (aka-Moose) replied 1 year ago.

You wrote-----i guess. tell me what ill be looking for because man its scary driving it.

I wrote-------You need to look at TPS and MAF/MAP readings. Fuel pressure is checked with a gauge.

You wrote-----ok ill let you know. thanks

I wrote-----Super

You wrote-------?

If you wrote another question, I did not get it.

Customer: replied 1 year ago.

ok ill let you know. thanks

oh, actually there was a map code but i reset it last week. po108 . would this cause the problem i am having?

Read more: http://www.justanswer.com/gmc/9dnp2-gmc-1500-series-96-gmc-1500-4-3l-lately-when-putting.html#ixzz3q5BiN7LZ

Expert:  Chris (aka-Moose) replied 1 year ago.

A map issue can cause running issues. I can send you diag steps in a private contact if you ant them.

Customer: replied 1 year ago.

ah, like running when stepping on the gas issue or are you talking about starting or something like that?

Expert:  Chris (aka-Moose) replied 1 year ago.

A map sensor can cause starting and running issues.

Customer: replied 1 year ago.

ok so if any of the readings under acceleration go to zero or change by a huge percentage that is the problem?

Expert:  Chris (aka-Moose) replied 1 year ago.

That would indicate that sensor is faulty.

Customer: replied 1 year ago.

ok thanks ill let you know

Expert:  Chris (aka-Moose) replied 1 year ago.

Thanks

Expert:  Chris (aka-Moose) replied 1 year ago.

As mentioned in my first response, I would stay in contact with you. I've noticed you have not rated the post. So I assume you were not pleased with my help. I hate that you have spent money to get an answer but left not happy. Can you tell me why, or can I help more. If its more help you need just reply and we can pick up where we left off.

Customer: replied 1 year ago.
Ok so short term fuel trim bank 1 sensor 1 is contantly fluctuating where short term fuel trim bank 1 sensor 2 is sitting at 99.2% the entire time while idling. Fuel trim bank 1 sensor 3 is the same also- doesn't move off 99.2
Expert:  Chris (aka-Moose) replied 1 year ago.

Are these the O2 sensor readings or the fuel trims? Fuel trim should be +/-10 preferably hovering right around 0.

Customer: replied 1 year ago.

yes i am reading it right now- long term fuel trim- bank 1 = 25.0%

long term fuel trim- bank 2 = 25.0%

...and these below don't move at all no matter how i move the truck (or idle)...

short term fuel trim bank 1- sensor 1= 2.3%

short term fuel trim bank 1- sensor 2 = 99.2%

short term fuel trim bank 1- sensor 3 = 99.2%

Expert:  Chris (aka-Moose) replied 1 year ago.

At 25% that means the computer is dumping alot more fuel into the engine than needed because the readings its getting from the O2 sensors, indicates it is running lean.

Customer: replied 1 year ago.

all 3 o2 sensors are fluctuating nearly identically. at idle they seem to be between .600- .885. none of them seem to be malfunctioning.

Expert:  Chris (aka-Moose) replied 1 year ago.

I think I have offered all I have. I am going to opt out and let another try. Best of luck.

Customer: replied 1 year ago.

my friend told me this could be a compression issue? any chance on that?