chevyboy07 91

i am having a very hard time figuring out an idle surging bug i have guys. I have had an Accel AFPR on the car since practically stock and never had any problems.

Fast forward: heads, cam, etc put the car back together and had an idle surge problem ever since. I am pretty darn sure its not a vac line leaking. They have been changed, checked, etc, etc. New injectors, fuel pump, etc all check out good. Car runs awesome cruising or at WOT, but surges about 500-70 RPM at idle MOST of the time. it will also surge at about 1500 while cruising. it seems like it runs out of fuel then comes back to life for a second (plus the A/F guage falls on its face so i know it did go lean for a sec)

I think its the FPR b/c i took it apart during the heads/cam swap and inspected it and put it back together (very carefully). I DID notice i put it back together OFFSET by one screw the way it came off. The cap went on 1 click counterclockwise the way it originally came off (my bad), but i dont think that should have affected it. Maybe it did??

The diaphram looked good, etc.

So i hook up a vac guage and these are my #'s at idle. I have a pretty steady fluctuation between 10-15 in Vac Hg.

For starters that is low compared to the "norm" (17-22 "). So its LOW and fluctuating....ANY TAKERS??

Also, after the heads/cam, i decided to step up to a frsh motor. New everything. I can tell you the intake is sealed, TB sealed, etc etc...its all friggin sealed up!!! still same problem on the new motor.


THANKS....(BTW no fuel in the vac line at the regulator)

Also, when i check the fuel pressure, the guage goes crazy between 40-90 psi fluctuating like crazy. Nothing changes when i rev it up...it just does it faster and faster

CEP89

Sounds like a problem with your fuel pressure regulator. Your vacuum test indicates too rich or too lean. I would take your FPR apart again and reassemble it. Is there anyway you can swap in another FPR to test with?

MrDude_1

do you still have EGR hooked up?

the surge, esp when crusing, is common with EGR valve problems.

8Mike9

Assuming you put everything in correctly and nothing went bad during the swap...

Basetiming first, then

I'd suspect the valves needs adjusting...the swing in vacuum is what's causing the rich/lean condition...it's making the FPR output change, IMO.

Depending on how large the cam is, you may need to do some PROM Tuning as well.

chevyboy07 91

CEP89: i have no other one to test with. I am going to have to buy one it seems. (this is my next step)

MrDude: EGR is not hooked up. I have the actual valve installed where it belongs and a block off plate at the back of the SDPC manifold where it has the provision to plumb into the exhaust.
Also, I flagged it in the tuning so it does not look for it.

8Mike9: base timing @ 6 deg BTDC as stock requires. Played with a little more and a little less>> no difference. You make a very smart point in saying the swing in vac is what's causing the FPR output change, HOWEVER the FPR fluctuations are extremly fast and very dramtaic. The vac fluctuations are "softer" and not as fast. Meaning their tempos do not coincide. I would agree if they had similar beats, but they dont.

Tuning has been done both professionally and by me (Im pretty decent and its not my first). I actually have a "real" tuner working with me also.

Also, it is more than likely NOT late valve timing i am pretty sure. If it were i should see readings in the 0-10 range. The #'s say it MAY be late ignition timing...that is the 14-17 range. I am in the 10-15 range, so numerically its possible (but i checked it, verified it, etc) my timing should be on the money!

Also, i am an engine builder & restorationist by day....so this is a slap in the face LOL.

I mean, Mid-Year Corvette restoration is our thing.....none of the guys here want to even look LOLOL.....jerks

They seem to forget that THERE ARE FUEL INJECTED 'vettes in our year range of specialty!!!!

i think i may pull the regulator and see :/