Thanks for the wealth of information on this site. I have had on and off problems with my blazer for a couple years now (stuttering, hesitation, surging at certain RPMs), and I am hoping I have it nailed down but wanted to get some input from the folks here.

Basically my blazer on and off seems to have a stutter, mostly at low RPMs under medium load, and intermittently. If I floor it the stuttering stops. So far I have replaced:

EGR valve
Plugs
Wires
Cap
Rotor
Distributor (broken tab on original)
Coil pack
Fuel filter
CFI TO MFI conversion (updated spider + regulator)
TPS

The latest replacement was the spider/fuel pressure regulator, and it actually seems to be a little worse now? It ran fantastic for the first day, then it rained for a couple days, and now is back worse then ever.

I just went down and bought a fuel pressure gauge, and it basically registers 50 PSI.

50 PSI at prime.
50 PSI at idle.
and then will drop down to about 40 PSI after 10 minutes.

From what I've read here, it sounds like maybe a bad fuel pump, but my Haynes manual says that 55-65 with a 3-10 PSI difference is acceptable?

I also ran across a thread that said something about corroded grounds at the back of the truck can cause an issue, and one of the symptoms can be a jumpy fuel gauge, which I have seen happen on rare occasion.

The thing that made the biggest difference was the fuel filter, I actually thought the problem had been fixed for a couple of weeks.

Another strange thing, it seems to be worse when it very humid and or rains for a few days?

I don't have any current codes, but I did at one point have a lean condition, which lead me to replace the spider.

Any feedback would be appreciated.

 

That pressure is quite low. The next step would be to install the pressure gauge on the line that runs from the pump to the filter which will isolate the pump. If the pressure is still low there or still drops off, then the pump is at fault and you need to look deeper into why (wiring or just a faulty pump).

 

I should mention, when I say drops to 40 psi, that is after it's been OFF for 10 minutes.

 

The pressure must remain above 50psi for 10 minutes after the pump shuts off. If it doesn't, there is a leak in the system. Isolating the pump tells you whether the pump is at fault or if the spider/FPR are at fault.

 

my 2000 blazer was also surging at low rpms, i had the spider injector replaced and it was still surging come to find out it kept shifting in and out of overdrive so i think the transmission shop had to replace sylnoid in the transmission and it stopped

 

have you changed out the gas filter?

 

I replaced the fuel filter a couple months ago, and it ran like a champ for several weeks, I actually thought the problem was solved, but then it started again, which lead me to the FPR/Spider replacement.

Thanks for the response Bubba, did it happen in reverse? Mine, especially after a cold, facing downhill start has issues backing up with the sputtering. It's really strange because when it's not happening the truck is running like new.

 

I know this may sound crazy, after only changing the filter a couple of months ago and it ran like a champ!!! Change it out again, you could have poss gottena tank of gas right after a delivery was made to a gas station and all the crud at the bottom of their tank was pumped into your tank and when you start getting low on gas that crud is getting drawn into your filter again,,, try changing the filter again and see what happens, if it runs like a champ again,,, then i would say drop the tank and have it cleaned... tip of advice: never get gas from a gas station that just recd a delivery or is in the middle of delivering gas..

 

i replaced all of the same things as you, as well as the fuel pump and still it does the same exact thing, im starting to get pissed!

 

did a little research? have you put a timing light on the wires? it could be the distributor drive gear that is bad. it helped someone else and they had the same problems
V8S10.ORG • View topic - Solved - '97 4.3 Blazer hesitation, P0300 - random misfire