'96 S10 ZR2 4.3L Stalling/Hestation issue

Extended Cab Truck 153,000 miles. I have had truck since new with no problems other than normal maintenance issues; tune-ups, sensors, etc.. I did replaced the fuel filter and fuel pump 9 months ago. I did a tune-up during the summer; plugs, wires, cap, rotor, etc.... with quality parts and it ran fine.

The symptoms started about a week ago. I had a rough idle and after the engine would run for about 10-15 minuted or 8-12 miles it started to hesitate on acceleration from a stop. I thought maybe I had some bad gas, so on my next fill-up I ran a higher octane fuel to see what would happen. It didn't change the hesitation. Then on Saturday it started the same hesitation in the same time/mile frame which ever comes first, except this time it stalled after the second stoplight hesitation and would not restart for a few hours. I then put "STP Injector Cleaner" and "STP Fuel Dry" in the gas tank incase I had a water issue. I drove it to work today and yes same exact thing happened in same time/mile frame and it stalled under a stoplight and would not re-start.

My "check engine" light has been on for a few weeks with an O2 sensor code. I have not changed the sensor yet. I don't think it is the O2 sensor because I have driven it before with the O2 sensor code (my O2 sensor goes bad about every 20,000 miles or so, just figure poor quality part). But I could certainly be wrong.

I have read through the posts similar to this issue and have not found a clear fix or resolution other than changing, EGR, Ignition Module, Coil, TBS, AIC, etc... Is there any specific item I should start with or may it be something else with the symptoms described.

Thank You for any Help

ZAP

I think it sounds like a perfect opportunity for KISS. You said that you have worked on most everything that should have an affect here..except the O2 sensors. You've had O2 sensor codes periodically. Those O2 sensors don't come into play until the engine is warmed up..which is when you start noticing the problem...sounds like it is time to change'em huh?...they have done there job well enough so far, they don't last forever though.
Rando

Changed O2 sensor, no change. As I said before have had O2 sensor codes in the past and ran fine until and after replacement. Any other ideas?

ZAP

Changed O2 sensor, no change. As I said before have had O2 sensor codes in the past and ran fine until and after replacement. Any other ideas?

ZAP

Is there only one 02 sensor on your model truck? Some have 3.
The EGR would be the next thing I would check, along with the fuel pressure in case your pump is going bad.

Yep, have you replaced all of them? If that's not it then I think you have already done anything else that I could think of. Really sounds like an O2 sensor issue though. Good luck

EGR, Ignition Module, Coil, TBS, AIC, etc...I have not changed these items, I was inquiring about them after reading posts. The only O2 sensor I replaced and that has ever given me ploblems is the one on the exhaust at the 'Y' pipe. I am not sure where the others are. My "check engine" light is off after replacing O2 sensor. Where is the EGR so I can clean it with carb cleaner as other posts advise?

Another thing, the duct from my air filter to the throttle body with the mass air flow sensor continually comes apart. It comes apart where the outlet on the air filter cover mets the mass air flow sensor. I was looking at the mass air flow sensor last night , because it had come apart again, and it looked very dirty from 10 yrs of coming apart and drawing intake air thru mass flow sensor with no air filter in-line. Could this be my problem, is there a way to clean it, or do I need to replace?

One last thing, I replaced the fuel pump 9 mos ago with a new AC Delco. If I did not get the O-ring back in the tank correctly and I do have moisture in the tank could that cause the same or similar symptoms? I ask because I had trouble getting the pump assembly and O-ring to seat into the tank flange at first, then suddenly in slipped right in and seemed to seat, I didn't want to pull the pump assembly back out to see after the trouble I had getting it in.

Thanks in advance

zap

I apologize, I misread the earlier post- I thought you had already changed out that other stuff. I have seen where O2 sensors don't always cause a CheckEngine light at the dash...no actual code but poor performance just the same. At 153K miles I imagine they could all need changing out anyway. maybe someone else with more experience could help with how those other componants come into play...
You probably should clean the MAF, and you can pull the fuel filter and drain it in a jar- could show if any water is in it, run a line/hose into a bucket, turn the key to the on position (but not actual crank position and let the pump put some gas into the bucket also..) I think water in the gas would do just as bad cold or hot though and you'r problem starts after warmup right?

Yes, the hesitation/stalling starts only after warm-up. But it does idle a little rough cold and gets worse as it warms up.

Where are the other two O2 sensors located, I will replace them also? Where is the EGR located? I will clean or replace tonight and see if that helps. Would cleaning the MAF do any good, dumb question its dirty I need to clean it reguardless, but after cleaning could it help this issue?

Thanks

zap

The O2 sensors are in the exhaust pipe both before and after the cat. conv. Depending on your year model, either one or two in the manifold/front pipe- the egr is on the back side of the engine, I've not had to remove mine so I can't give too much advice---Chilton's book tells how to test (both actually) and the EGR symptoms also sound like what you describe...could be the culprit. Sorry I'm not more helpfull, I'm only a light duty backyard mechanic..but according to the books either could be your problem.

Yes, the hesitation/stalling starts only after warm-up. But it does idle a little rough cold and gets worse as it warms up.

Where are the other two O2 sensors located, I will replace them also? Where is the EGR located? I will clean or replace tonight and see if that helps. Would cleaning the MAF do any good, dumb question its dirty I need to clean it reguardless, but after cleaning could it help this issue?

Thanks

zap


http://www.amazon.com/CRC-Mass-Flow-Sensor-Cleaner/dp/B000EGH57G

Clean it, but use the right stuff so you don't ruin it.

And use this:


http://autozone.com/servlet/UiBroker?ForwardPage=az/cds/en_us/0900823d/80/19/0e/ba/0900823d80190eba.jsp

The EGR is easy to get to and clean.

Also even after putting a new o2 sensor sometimes the computer needs time to reset, as it uses data gathered when the sensor was bad.

Sorry I didn't get back sooner. It was the fuel pump again after all!!!!