5500 rpm hang

[The Radium King]

hi there. have a 3.6L X51 engine that is new to me. it seems to have a hang at 5500 rpm. if i'm hard on the throttle it'll move right through it, but if I pass through it slowly it'll hang for a sec then continue to rev. I thought it might be a gummy resonance flapper but no dice. no codes. deviation is good. I do have a pst2, so if anyone has any advice, can tell me what to look for, or point me in the right direction I would appreciate it.

[Loren]

Have you tried cleaning the MAF? (use only MAF cleaner)

[The Radium King]

well golly. I ran my pst2 and logged rpm, maf output, cam positions and throttle positions. everything seemed to track appropriately as I worked through the rpm range except the maf signal - it does a little spike at 5500 rpm then flattens out ... i'll try cleaning it or swapping in a known good maf.

[The Radium King]

so, update. cleaned the maf, fired it up, same issue. cams seem to be working ok from the log, maf still flat-spots at 5500 rpm. so, logged throttle position and it looks to do the same thing. so, it looks like the throttle body is jamming or something. anyone heard of such a thing before I tear it apart?

on another note, when I activate the valve lift with the pst 2, the car stalls - this what is supposed to happen? cheers, trk.

[Ahsai]

Did you also log the gas pedal position sensor? If so, does it also flat spot? The stall I think is normal. Same on my engine.

Edited August 23, 2013 by Ahsai

[apex944]

>> it looks like the throttle body is jamming or something.

This would be independent of RPM. Don't tear it apart yet.

[The Radium King]

I was thinking there might be some congealed goo sticking the TB at one spot on its trip through full range of travel - all my testing has been at no load so the sticky spot might be consistent. opened it up and no goo, so going to try logging pedal position, throttle position, maf and rpm; might be a flat spot in the pedal pot. thanks all; i'll report back.

[The Radium King]

so, logged pedal position and throttle position; pedal is fine but throttle flat spots. time to swap in a new throttle body.

[bzguy]

having had similar 'hesitation' issue, I replaced the MAF & it solved all my problems ; I tried cleaning it first, looked like brand new, but if it's broke, you might not even see it.

[The Radium King]

I actually disconnected the maf altogether and got the same result.

[Loren]

I actually disconnected the maf altogether and got the same result.

Then I think you have proven the MAF is not working like it should.

[The Radium King]

ok. no codes whatsoever and had flat spot issue with maf connected. disconnected maf and got maf and iat codes but same flat spot at same place. my understanding is that, with maf disconnected, computer defaults to fueling based on throttle position. this would indicate an issue with throttle body, no?

[bzguy]

As Loren says : if you remove the MAF and there is no difference, then most likely the MAF isn't working at all.

I had a similar issue, followed the forum members' advise : MAF still looked brand new, cleaned it, removed it to test (made no difference), replaced it and all is as it should now : no hesitation, no hiccup, no flat spots, just perfect !

My guess (as from what I have learned here) : MAF !