i have a moderately modified s10 extreme with an issue. i think it's the cat, but whenever i punch it the motor sputters and even stalls! think the injection is starving the motor.

645

Asked by Mar 02, 2012 at 12:37 AM about the 1999 Chevrolet S-10 2 Dr LS Xtreme Extended Cab SB

Question type: Maintenance & Repair

it's a 4.3 vortec with a k&n cold air intake, a flowmaster cat back setup, and a hypertech performer. the cat has been punched
out and i plan to replace it but with a high performance setup like this it's hard to believe it would cause such big issues. any
thoughts?

31 Answers

5

is it throwing any codes?

525

There is a long list it could be. Check for codes. check mass air flow and fuel pressure,

645

only code it's throwing is the o2 sensor after the cat.good idea about checking fuel pressure, it never occurred to me it might be the fule pump or a clogged fuel filter

525

yeah it is a good possibility

615

Try adding a bottle of, " Fuel Injector & Carb Cleaner" to a Half Tank of gas.. That worked for me!

645

i've replaced the whole ignition system with MSD components, and all but the pump in the fuel system and it still isn't right. i think it's the pump but that should cause it to not even start, right? any thoughts?

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16,255

Is the k&n filter oil charged? Those are bad for the maf sensor.

645

thought of that, but after cleaning the filter and changing the maf the problem persisted. i found that the sppider unit that sends fuel to the individual injectors was bad so i replaced that, now i'm certain it's the fuel pump or the circuit. those are the only 2 possibilities.

16,255

Throttle position sensor may be bad. Or even the MAP sensor. Both are easy to test.

1 out of 1 people think this is helpful.
645

yeah i ruled those out early on, thanks though

16,255

How is your fuel pressure?

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645

35 psi

645

leaks down quick too, so the check valve and pump mechanism itself are both bad.

16,255

35 is low for a 4.3. Needs to be above 50 for sure. And the leak down could be the dreaded fuel pressure regulator on the spider assembly.

1 out of 1 people think this is helpful.
645

no, i replaced the spider. it's the check valve in the pump assemble. i've been looking into doing a walbro inline conversion... looks simpler and more reliable but it requires some ingenuity.

645

it was 700 dollars for the whole spider assembly and 6 new poppet injectors.

16,255

I would find a way to isolate the pump and test it that way. I have replaced the spider in my old truck to just have it fail a few months later. I SWORE it wasnt it, but as it turns out... Also some replacement fuel pressure regulators that come on replacement spiders are adjustable, they are supposed to be set correctly but that isnt always the case. However i hope it isnt your spider. Do you have access to a scan tool that shows fuel trim? that way you can see if it's leaning out the system, or trying to richen it.

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645

it was ac delco so i hope it's trimmed right but i'll have to check it out. also with that low FP, would the trim really tell you much except that it's extremely lean?

16,255

Sorry about the delay. I am curious about the fuel trim becasue it can give you a hint if there is a leak under the upper intake or not. If there is a leak it should be trying to lean it out and show a negetive number. If it's not leaking there it will be trying to richen it up and show a high positive number. If it's not leaking in the intake then the pump/filter are suspect.

645

right, right. i see your point. also wht's your opinion on poppet injectors vs the newer style injectors available? even though they're brand new my injectors stick when i put it to the floorboards.

16,255

The setup with 6 injectors is better than the single with poppets. How do you know they are sticking?

645

if i roll onto it it'll accellerate okay even though it's having a really lean condition (indicated by codes and plugs) but if i give it gas too quickly it flattens out, starts misfiring badly.

16,255

Its because the system is running poorly, a quick change will make it stumble or stall. A gradual change will allow it to ease up the rpm's. I dont think it's your injectors. Still thinking fuel filter or pump. Possible miss adjusted regulator. Rule out filter first, then there are 1 of 2 ways to go about this. Either make an adapter for your fuel pressure gauge to hook up where the line runs into the fuel filter and read pressure there, it should go well above 55psi here WELL above, dont run the pump long testing like this, you shouldnt need to. Or take the upper intake off and try to adjust the regulator, mine had a torx bit in the center to turn.

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Best Answer
645

now wonder you got over 2000 rep lol

16,255

I've had alot of experance with 4.3's and the spider injection setup.

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645

did you ever do a fuel pump conversion? i'd like to do an in-line setup. most people reccommend the walbro 255lph model. do those fuel socks on the bottom of the in tank pumps ever get clogged? seems like they could.

16,255

they can get clogged, I've never done the inline pump swap. I have looked how to do it. The Walbro looks like a good one, but you would still have to drop the tank and remove the old pump and make a straight line into the tank for the inline because you cant suck through the factory pump. If you get a legit ACdelco factory pump it shouldnt give you problems for a while, however i've used aftermarket brands that worked good too. It's all about electrical grounds, the pump motors will burn out because they get low voltage due to a bad ground. The factory pumps cool themselves with the fuel returning from the regulator so low voltage=low pressure=little return=hot pump. You engine will run with the lower pressure becasue the pump can push out above 100psi, so half power is still above 50psi. Test the pressure isolating the pump and check leak down there too before you go part swapping, unless your just bored and want to tear into things.

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645

huh, so when i do change the pump i should probably install a new ground wire as well then. only problem i have with the ac delco pump is i don't generally have 400 bucks right now.

16,255

Thats why i want you to test the pump by isolating it, just to be 100% sure a several hundred $ part is to blame. But yes when you replace the pump ensure a clean ground connection.

1 out of 1 people think this is helpful.
645

will do man, thanks for all the help andrew! now i'll commit your advice to a couple of things and see where she's at!

1,535

With all the mods you have done to this set up,have you looked in to changing he chip ? The MAP sensor will also make it "fall on it's face". O Riley s have fuel pumps for under $150

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