Specs 1996 4x4 Blazer, V-6 4.3 L
Problem is only after the truck warms up. Then it will sometimes bog down when the gas pedal is pressed hard, versus a slow acceleration.
The fact it does not do it on a cold start, for me rules out a lot of obvious suspects, including the maybe the P0102 code????
MAF is clean, and the scanner shows it responding to engine rpm changes.
Code P0102 , low air flow reading on MAF sensor. That means the computer "Thinks" the reported air flow from the MAF is less than actual based on the MAP, data tables and O2 sensor data etc.....
No other codes
New
TPS (durajunk) but I think the problem was there before the TPS was replaced?
Fuel pump (there was trash in the tank) (did not solve the problem)
New fuel filter (Was no help)
-------------------------
MAP and IAT/MAT air temp sensor look new,
No signs of sensor connector issues, look clean and newish.
My Snap-on MT-2500 shows STFT and LTFT to be about 5% high, both locked at about 138 (128 is the mid point, sweet spot, on a 0-255 range), and the STFT was not changing as I moved the gas pedal, which is a question in my mind???
O2, TPS, MAP, MAF live data look normal on a first look, all live data, but have not run detailed tests.

My experience is with other brands, Jeeps, Fords, Saturns, and some limited chevy stuff...But does this set of data jump right out and indicate any common issue
on the this rig the experts have seen regularly?
The problem is not continuous. It is random, but does not happen till the engine is warmed up. It happens at stops and while driving, when the throttle is pressed to fast.
But is random, which makes it real hard to pick a usual suspect(s) to focus on?

Clean the EGR maybe????

 

So do you have any codes and if so which ones?

Please show your STFT and LTFT for each bank (4 numbers total), including sign stated as +/- XX.X%, usually between 0 and 25 for a given number. Pls generate those numbers at idle, 1500 and 2500 rpms.

Use live data to obsereve the TPS position while smoothly opening and closing the throttle with the truck not running and see if the reported TPS position has any glitches in it.

Did this problem start right after any changes to the truck?

George

 

Found the vacuum reservoir, and several very wet, sticky, old (cracked) vacuum lines near it/connected, but two were 50% split right at the nipple, repaired those two huge leak spots less than 6-9" from the vacuum reservoir.
Cleaned the EGR valve, cleared the only code (see post #1), and it still has a hesitation/miss at 35-65% throttle (Kinda like a throttle limiter).
I am leaning towards it being a leaking FPR.

Nothing else makes any sense and all the scanner data says everything else is working. Unreported excess fuel delivery could be mistaken by the 96 computer as unreported air flow, I think. I think fuel is leaking out the vacuum port of the FPR. I hope we caught it early.

I think the P0102 code is a read herring of sorts, unless one knows how and why all this stuff works...

Who was the GM sadist that installed it under the intake manifold???

Will test fuel pressure Monday to confirm.
OH, he also has priming issues, indicative of a leak in the FPR!!!!!

 

I suggest You follow George's advices and post LT/ST trims. But do as You prefer...

 

The data I got is in the original post, including fuel trims. TPS past all the tests. I am pretty sure the gunk all over the vacuum hoses near the Vacuum reservoir bottle ((on the hood) was from gas, from a leaking FPR regulator. I'll post up when we have that data. The fuel trim data was unremarkable.

 

 

Any one have the FSM fuel pressure specs?????

 

 

" You don't know if your fuel trims are unremarkable yet " Actually I do know. I explained in the very first post, they were both flat lined, locked at a hair above neutral. Neither changed at any condition.

Thanks for the fuel pressure info!!! :-)

Checking fuel pressure right now.

 

OK, it is not the FPR or fuel pressure. It holds pressure nice and steady at 60 psi after the prime, engine off and when we stomp on the gas pedal it jumps to 60 psi.

And during deceleration it drops back to no less than 52 (or was it 55? I forget) but it looks normal as hell to me based on similar systems on Jeeps and Saturns and Fords...I have experience with in this year range

I ran some tests, and the engine runs fine cold with no MAF connected. I found that interesting.

Exhaust is not blocked. So it is not a bad Cat.

After clearing the codes, I got live moving fuel trims. In summary the fuel trims, all 4 start at the baseline of +128 (normal) at idle.

My scanner, Snap-On MT-2500 (professional rig) reads fuel trim as 0-255, and 128 is what you all probably call zero (OBD-II style testers)?

Then they both climb evenly across the two banks with both banks reading +/- less than 5% difference across both banks, maybe less than 2%. So the problem is not bank dependent. But at idle it started at about 129 ST and 160 LT on the second restart test (had cleared codes a few minutes earlier, ran it till it died). Both were 129 right after clearing the codes etc.

Interesting note is that once it dies, it always restarts immediately, so that kind of rules out any over heated parts that need 5-10 minutes to cool off to work again. Something in the computer is resetting????

So the first test batch at idle, about 600 rpm, ended up ST=129 LT=160

at 1500 rpm ST=192 LT 160 after 1-2 minutes, at which point it died.

At 2500 rpm after about 2 minutes ST= 192 LT=160 when it died.

Fresh start after it died, at 2500 rpm ST =128 and LT=128 at first and climbed pretty fast, and died again in less than 2 minutes.

At 600 RPM ST and LT rose to 160 on both, on both banks and then it died. Took about 3-4 minutes.

Inj PW is running 3.7 to 4.0 mV when I checked it early on and the MAP read 36 KPa at idle and MAF read 5.1 g/sec at idle when I began all the tests.
We are at sea level.
Ambient air about 78 F.

It has thrown a P0102 code before, Like I posted in my original post!!!!! Sorry, but I find a bit irritating to be asked a question I already answered in the original post about codes.

And before I cleared the codes the ST and LT fuel trims were static, they did not change at all in a 10 minute test the day I made the first post here. That is why I said in post one they were unremarkable, meaning they did not change and all four were locked at about 138, just wee bit over the 128 normal sweet spot.

It was like the computer was using a data table and ignoring sensors??? After I cleared the P0102 code the fuel trim was live again, which is what I just listed above.

It acts like something electrical is quitting when it gets too hot. But I am ruling that out since it immediately restarts???

I am not new to MAF sensor technology, I am an engineer, I could teach a course on them and the theories involved, LOL, Chemical Engineer, 2rd generation...... but I have no experience with their malfunction symptoms on these vehicles, YET. That is why I posted here.

I now hope one of you has some clues to help narrow it down. Today''s fuel trim data (after clearing the code) is very interesting and I think very telling. But does it all point to a bad MAF, or something else? There have been no other codes at all.

Also this thing has almost zero miss fires in say 900 cycles, when I checked the scanner. Maybe 1 miss fire total in a 5 minute run. So that part seems to be running incredibly well for 1996 with about 150,000 miles on it. That was checked before it died!!!

I am running of out ideas, except the MAF itself. Does any one have an OEM FSM spec data set on how to ohms test the three connections? Or must it be tested hot, live with power to it and back probe it?

3 days ago, I checked my scanners MAF flow data readings and they were live, and moved up and down with changes in throttle-engine rpm. So my first thought was that it must be working? But it could be biased, and giving bad data....Hard to know how to confirm that with out a calibrated flow or factory specs?