bobl

The set up is this. Whipple charged 555 with Holley HP electronics. Roughly 1000 HP. The engine is tuned great and runs great. The issue is after idling for 2+ minutes the engine will go dead rich upon acceleration at 2000 +/- rpm, just for a a second or so, but enough to cause a noticeable stumble. It does this one time and then runs perfect until it’s allowed to idle again for over 2 min. The idle a/f stays correct, it only does this as the throttle is slowly advanced and comes in around 2000 rpm. I’ve done detailed analysis of data logs and real time. What I have determined is that the pulse width is not increasing excessively during this time so it’s not the ecu commanding more fuel. I’ve been able to make some changes in the the fuel map and correction to mask the problem but I’d really like to understand what’s going on. My thoughts are that it’s possibly fuel falling out of suspension or pooling due to throttle body injection and cold intercooler. Another thought is that it could be a reversion issue and intake charge is getting diluted. Thus I’m really seeing low oxygen level instead of excess fuel. No actual signs of water reversion. I would welcome some knowledgeable discussion.

Bob Lloyd

BUP

iTrader: (9)

just throwing it out on top of , injector spray patterns and or slightly leaking injectors, Too much or out shape spray pattern hitting the wall of TB and or intake manifold causing poddling ? runner shape or design ? Intake manifold temps ?

bobl

Good thoughts. You would think this would show up just idling. Injectors were just cleaned and tested. Intake temps do get warmer at idle. The intercooler is plumbed off sea water pump so it's flowing at idle, but IAT temps still climb quite a bit. Tried blocking it off but no difference. It's a rear entry Whipple so not much runner shape or design to consider or alter. Seems to me warmer intake temps would have the opposite effect? Not sure.

Bob

QUOTE=BUP;4299484]just throwing it out on top of , injector spray patterns and or slightly leaking injectors, Too much or out shape spray pattern hitting the wall of TB and or intake manifold causing poddling ? runner shape or design ? Intake manifold temps ?[/QUOTE]

BUP

iTrader: (9)

Thinking out load but will have to think more about it.

Asking does this app have an actual IAT sensor - If so location of it could be the problem.

also just making sure 100 % TBI induction here and I am not missing the info ? I hear you about the injectors being tested. I know a bit about this form of service. Anyways spray patterns from these TBI injectors can be or always a problem and or dripping fuel droplets also.

The angle the TB is mounted and or is sitting when the boat is not up on plane can play a part as well.

I like to take still pics of the TBI spray patterns and also use a timing lite to watch the spray patterns - you can sometimes pin point how bad the spray patterns really are from TBI injectors. The timing lite helps a lot to see how the fuel is flowing and or what is really going on.

Anyways have a lot going on as well and need to get something done today. I have a bunch wanting to hit the water as well.

sutphen 30

where is the vacuum/boost line that goes to the fuel regulator?I'd also look at the routing of the return line,does it return to the tank or filter head?

HaxbySpeed

Bypass valve

bobl

This is the Whipple throttle body with 8 injectors mounted in it. The IAT is below the intercooler. FYI, this setup has been running for 10 years trouble free. So I don't suspect a problem with any setup issues. Problem just surfaced after rebuilding the engine with new heads, cam and the Holley ECU. Previously ran a FAST. Still kind of fine tuning with the new ECU and thus ran across this scenario. I guess it's possible the condition always existed but the tune was different on the FAST so it didn't manifest itself. What really triggered the investigation was it would go lean and backfire. What I found out was because it was in closed loop the ECU was seeing the momentary "false" rich condition and removing fuel. When the rich condition clears it would be too lean. Turning off closed loop cleared this issue, so I could then see what was really happening. Hope this makes sense.

S30-
Regulator is boost referenced from the base of the intake and return is to the filter head.

Bob

bobl

Good idea. The customer just replaced the bypass valve diaphragm because it wasn't working, but I did not personally verify it's operation. I had forgotten about that. I'll have him verify that it is indeed working correctly. He lives 200 miles away so it's hard for me to put hands on it. That very well maybe the culprit.

Thanks,
Bob

QUOTE=HaxbySpeed;4299613]Bypass valve[/QUOTE]

BUP

iTrader: (9)

Thanks for the update - also can you update the fix when done. Did not know the TB set up and thought at idle up to 2k rpms was the problem, I miss read AFTER the part of " runs perfect until its allowed to idle again for over 2 minutes". Hence why I kept throwing out TB injectors spray patterns.

bobl

Just spoke to him and yes the bypass was replaced and working correctly at that point. He'll recheck it. That does sound like it could be the culprit in this. The point it's going rich would be just about where it would start closing, around 85 - 90 kpa.

Bob

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