Hello! I have been having some issues with my 1991 S10 Blazer, and hoping that someone can lend some insight. It has 199,000 miles, Rebuilt V6 4.3 Liter Engine put in approx. 5 years ago, Automatic Transmission, 4WD. Here’s the story:
fficeffice" /><O></O>
A couple of weeks ago we noticed there was a fuel leak, and so replaced the fuel tank and the aft section of fuel lines (main, return, and vent - they were rusty and the main actually had rusted through!). We siphoned the gas from the old tank into the new one. I'm certain some dirt got into the new tank. A few days later, we started having issues when accelerating from a stop. The engine would hesitate and the car would drive jerky. We replaced the fuel filter, but that did not resolve the issue. A mechanic told us the fuel pressure was high (he put a pressure gage in place of the filter to measure the pressure). So we checked the return line for kinks and replaced the fuel pump and strainer. This worked, but again only for a few days. On the fourth day, it started hesitating and stumbling and so decided to try filling it with more gas. Then, right after getting gas, it was hesitant pulling up to the street. (The hesitation doesn't always happen right off of idle...the engine may speed up slightly before the stumble occurs) The blazer stalled when I hit the gas after being stopped waiting to turn. Then, when trying to reverse, it stalled two more times upon my hitting the gas. It drives well at higher speeds, but still has hesitant and jerky accelerations. There seems to be a certain spot where this happens more…and almost always happens when driving slow in 1st/2nd gear. The easiest way to make this problem reoccur is to put it in 1st gear, and slowly push the throttle and then once it starts to stumble if you hold it at that throttle position, it continues to stumble until you accelerate out of it where it starts to act normal. We unhooked the vaccum line to the EGR valve and still have the same problem. We changed out the TPS and still found that we had the same problem. The guys at Autozone recommended we check the timing to see if it is changing during engine acceleration. I still have thoughts that maybe there is dirt in the system somewhere? It just seems odd that we replaced the fuel pump/strainer and filter, and it fixed the issue for about 4 days of driving, and then started reoccuring again. Could the pump be bad again? I bought the AC Delco pump. What do you think? Any ideas on what to try next? Any help would be much appreciated!

 

a common issue when replacing the fuel pump is the wire harness isn't always replaced at the same time. most pumps come with this and it's also available seperate. it's the harness to the pump inside the tank. often the insulation will peel back, exposing bare wire. this can lead to early pump failure. if you did not replace this harness, then give it a shot. it could also be the pressure regulator, which is inside the throttle body. also, when was last tune up? plugs/wires/cap/rotor/air filter? has the idle air control valve been checked? any check engine codes?

 

There wasn't a 'harness'...the pump came with wires to replace the old wires, but not the 'plug/harness'. Therefore, we did not replace the wires, but we will check the pressure in the main fuel line and determine if it's a pump problem/pressure regulator problem.

I am curious about the idle air control valve? How would this be causing a problem?

The air filter has been changed recently (and is clean). I don't know when the plugs/wires/cap/rotor were last changed. The check engine light is not on, we haven't checked for any codes.

 

We resolved the issue. After checking the fuel pressure one last time, it was about 15 psi - which is a little high (for TBI the pressure is to be 9 to 13 PSI per my Haynes manual) . Then in glancing at the fuel lines running along the chasis one last time, I realized that the vent line and return line were switched. So the return line (the larger of the two) was being restricted by the smaller diameter return line, causing the engine to run rich, which in turn caused the stumble off of idle. There is a section of rubber line halfway down the chassis where they were switched when I replaced the aft section of fuel line. I switched them back and the issue was resolved! Thank you all for your time and thought in helping us solve this problem! Hopefully this discussion helps someone save some time in the future if they make the same mistake!!!