Hesitation Problems 99gmc 5.3L

[sierra 99]

Need help since GM can't seem to diagnose problem.I had my 99 gmc in numerous times to the dealer and they keep soaking me money for things that haven't cleared the problem up.They changed wires,plugs,did complete fuel injector cleaning,changed fuel filter,cleaned throttle body,put a chemical in the tank.So the problem is i am getting no codes,when stopping vehicle for 5mins then starting again and accelerating it has a bog,a big bog where you can floor it and it spudders and jerks and then it levels out and is fine.ANY SUGGESTIONS?Need a know it all for this one because the experienced trained mechanics at Gm can't fix this one...........Thanks

[Regalwhiskey]

How many miles are on your truck. Has the fuel pump been replaced?
Accurate (constant) fuel pressure is important to the computer which is responsible for mixing the fuel ratios.
I'd start by reseting the computer and retraining it, by driving it some, using different throttle positions, and hitting passing gear. If it don't clear up, check out the fuel pump.

[sierra 99]

Hi,the truck has 129000km's on it and the computer has been reflashed twice,i have tried taking battery cable off a few times,it clears it up for about a day then back to the same ole problem.Is there a way to check to see if the fuel pump is going?I read some where on the net that a guy changed his temp sensor and it cleared the problem up.Is this sensor expensive?And is there just the one.Because it seems now days on the newer vehicles there is a sensor for everything.And if i start changing sensors this will get pretty expensive.I'm looking for a simple but inexpensive fix.Hopefully someone will be able to help me out,this has been going on for a year now/So if the fuel pump was failing wouldn't it have crapped out by now?

[Regalwhiskey]

I still suspect the fuel pump.It seems practical that with 129000km it's due for replacement if your planning to keep the truck. As a GM service advisor, I would recommend this to my business customers,as breakdowns and tow bills are not an option. I purchased a new MU1089 fuel pump on eBay for $120 shipped. I believe your truck will be the same part number. Local labor for installation was quoted to be $175, so I installed it myself. Lifting and sliding the pickup box rearward is the best way to install if at all possible.
Again I'd recommend this repair as preventative maintainence. You'll be miles ahead and it will probably fix the problem.

[maxwedge]

A FP pressure test should be done to avoid guess work here, 65 psi on cranking.

[MyTOY]

i've seen a couple folks with a trans. case (module?) prob that
was making the trans think it was in 4lo & was shifting right from 1st to 4th.
It's a longshot and I cant find where I saw that again but I thought it was
worth mentioning. GOOD LUCK

[Regalwhiskey]

Originally Posted by maxwedge

A FP pressure test should be done to avoid guess work here, 65 psi on cranking.

I agree max, but even when it might test good, the mileage tells me that intermitant problems can be occuring (expected) within the pump. Its 8 years old, and these pumps have a history of going bad. Check valve, low pressure, backfire ect. I'd put my money on the pump and not the sensors. Tell me how it turns out sierra99.

[sierra 99]

Hi,Regalwhiskey,the fuelpump was diagnosed as being fine.What i don't understand is GM called me at work and said it was putting out 50psi.But a total pressure of 57psi was the highest.GM then tells me that the pressure was misdiagnosed and the vent selenoid and cannister have to be replaced.Something about being plugged.Would this cause the problem? Then filling up the tank then test driving it and seeing if hesitation is still there.They are wondering about tank being full/half/1/4 to be sure.I said the hesitation is there full tank or not but,That will cost 546.00 installed. or if by chance it is the fuel pump 818.00.installed I can't spend this much money on an assumption.Any ideas what i should do?I am going to try taking the gas cap off when it acts up to relieve the pressure if there is any to see if the selenoid is creating a vacuum that may be creating this problem. Will keep ya posted thanks.

[sierra 99]

I tried the taking off the gas cap trick it helps but doesn't eliminate the problem.Any suggestions??

[maxwedge]

I don't understand this, 50 psi is not good. The cannister vent issue would set a code. Whatever they do/recommned make sure they guarantee this will repair it.

[sierra 99]

Good news guys,after further extensive diagonstics the problem was the Mass Airflow sensor.Problem fixed yey Thanks for all the input guys and will definitley be back if another problem stumps me.

[99 shortbox sierra]

My 99 is doing that exact thing, how did you come to find that out, did it show up on a system scan?

[dimrod]

Wow. I stumbled across this thread. My exact Sierra has been doing the same thing for two years now. Start it up cold or hot and it has zero power even when stomped to the floor for about 1/4 of a mile. Then after that the gremlins work out of it and it runs like a champ until you turn it off again. I had the fuel filter and fuel pump replaced. No change. No codes come up. I even cleaned the MAF. Do you think my problem would be solved by replacing the MAF? Or is it just a crap shoot?

There is no dealer where I live (have to ship the vehicles in by air or barge). It's up to me or the local independent mechanics to solve the mystery. Forum help is appreciated and welcomed.

Thanks.

[Z15]

Has a oiled air filter been used on these vehicles? A K&N for instance?

See below.....

Info - Automatic Transmission Shift, Engine Driveability Concerns or Service Engine Soon (SES) Light On as a Result of the Use of an Excessively/Over-Oiled Aftermarket, Reusable Air Filter #04-07-30-013A - (Jan 25, 2005)

2005 and Prior GM Cars and Light Duty Trucks

2005 and Prior Saturn Models

2003-2005 HUMMER H2

This bulletin is being revised to add additional model years and to clarify warranty coverage. Please discard Corporate Bulletin Number 04-07-30-013 (Section 07 -- Transmission/Transaxle).

DO THIS:

First, Inspect the vehicle for a reusable aftermarket excessively over- oiled air filter.

DON'T DO THIS:

DO NOT repair MAF sensors under warranty if concerns result from the use of an excessively/over-oiled aftermarket, reusable air filter.

The use of an excessively/over-oiled aftermarket, reusable air filter may result in:

• Service Engine Soon (SES) Light On
• Transmission shift concerns, slipping and damaged clutch(es) or band(s)
• Engine driveability concerns, poor acceleration from a stop, limited engine RPM range

The oil that is used on these air filter elements may be transferred onto the Mass Air Flow (MAF) sensor causing contamination of the sensor. As a result, the Grams per Second (GPS) signal from the MAF may be low and any or all of the concerns listed above may occur.

When servicing a vehicle with any of these concerns, be sure to check for the presence of an aftermarket reusable, excessively/over-oiled air filter. The MAF, GPS reading should be compared to a like vehicle with an OEM air box and filter under the same driving conditions to verify the concern.

The use of an aftermarket reusable air filter DOES NOT void the vehicle's warranty.

If an aftermarket reusable air filter is used, technicians should inspect the MAF sensor element and the air induction hose for contamination of oil prior to making warranty repairs.

Transmission or engine driveability concerns (related to the MAF sensor being contaminated with oil) that are the result of the use of an aftermarket reusable, excessively/over-oiled air filter are not considered to be warrantable repair items.

[dimrod]

The airfilter has been changed once. I placed in a FRAM replacement, just a paper one like the OEM. The vehicle has 68,000 miles on it.