So for about a week now whenever I hit full boost(11psi)it hesitates almost like insane turbo lag. When I hit full boost my boost gauge will read 11 psi, but my afr on my wideband will shoot up to over 17 and the car hesitates and backfires. After about 3-5 seconds it will finally drop back down into the high 13's or low 14's(which is where I had it tuned before)and it will feel like it should on 11 psi. It's just for them couple seconds where it hesitates, backfires, and afr sky rockets. After that it hits like 11psi and does what it should. Any ideas?????
#107655, "RE: Weird hesitation while boosting" In response to Reply # 0
Anyone? I read where it might be the sfmu needs a seperate vacuum line but it's been t'd in with all the others for almost a year now. Just recently did it start doing this.
#107672, "RE: Weird hesitation while boosting" In response to Reply # 1
Your using the SFMU for fuel?
I have the same problem sometimes, the thing I hate about those units is the plastic balls inside them stick sometimes. Do you have your static pressure set and then used the idle screw to lower the pressure at idle?
Here is what is happening. When you boost the ball in the idle valve is sticking which doesn't let the SFMU pressurize like it should therefore it doesn't raise the fuel pressure high enough and you go lean. The ball finally seals off that air leak and then your fuel kicks in the rest of the way.
If you have a fuel pressure gauge you could watch it to see if this is indead the problem. To test this unhook your vac line from the SFMU and hook an extra line up. Blow in this line and see if any pressure leaks out of the SFMU. It shouldn't leak at all. Then fix your leaks.
#107686, "RE: Weird hesitation while boosting" In response to Reply # 2
So just get an extra piece of vaccum line and hook it up to the sfmu where the vaccum line attaches and blow in it to see if it leaks? Correct me if I am wrong but I will go check and get back.
#107687, "RE: Weird hesitation while boosting" In response to Reply # 3
Yea thats all there is to it. You could use a compressor and blow about 10psi in it if you have access to one. Try this test and let me know if it leaks or not. I am willing to bet that it does.
#107690, "RE: Weird hesitation while boosting" In response to Reply # 4
Well I disconnected the vaccum line to the sfmu and attached another on it and blew into it. I didn't hear or see no leaks.Did you mean when it is running? And your not talking about the bleed valve are you, b/c I don't have that setup yet. I checked my idle fp and it is where it has always been @ 48psi. I haven't drove it yet but didn't see anything different when I blew into it.
#107696, "RE: Weird hesitation while boosting" In response to Reply # 5
Thats weird, everything I have had a problem like this the SFMU has always been leaking pressure out. Is there anyway to watch your FP gauge while you drive? It has to be a fuel issue if your leaning out when it hesitates.
No I wasn't talking about the bleed valve, mine has always leaked from the idle screw hole. When you blew in the hose the SFMU pressurized and didn't leak any air? Does the car hesitate at lower boost levels? Like 2-3 psi? Maybe SFMU leaks under higher pressure, might want to check the screws that hold the unit together to make sure they are tight. They aren't suppose to be super tight but to loose they may leak.
#107705, "RE: Weird hesitation while boosting" In response to Reply # 6
I will check to see if ever single thing on the sfmu is tight again. I did see where the screw in the vacuum port was sticking out about even with the end of the port so I screwed it back in a little bit and checked everything else, but i will drive it around a post what happens.
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