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Matt
05-21-2001, 11:27 PM
I'm running a Pro Max that is supposed to run 34-36 psi fuel pressure. I run 34 psi at idle but I know my regulator is bad. I didn't get the chance to check the fuel pressure up higher in the rpm range before it leaned out and stuck #6 for the fifth time in a year. Here's my question. How low could the fuel pressure drop below 34 psi before I started having problems seizing pistons?

Thanks for any ideas,
Matt

RayBishop
05-22-2001, 01:50 AM
I'm not an EFI expert, but if #6 is the only cyl leaning out, I would think there is injector or ECU problems

RayBishop
05-22-2001, 02:28 AM
low fuel pressure should lean all cyls. sounds like your problem is dedicated to #6. I would suspect injector or ECU problems...

jimmyb
05-22-2001, 07:12 AM
raybishop is right that low fuel pressure will lean down all cylinders. However, the usually one cylinder will go down, and that cylinder is usually #6 (since it is already usually the hottest one)

as far as specifics of what fuel pressure would be too low, that is a crap shoot... it depends on your specific motor, air quality and temp, rpms, full throttle vs. part throttle, etc etc.

Matt
05-22-2001, 11:43 AM
All cylinders are definitely on the lean side. Like Jimmy mentioned, I figured #6 would be the first to go because it is always going to be the leanest hole due to it's location. Ray, we've suspected it was an injector or ECU problem all along, but Kinsler flowed my injectors and Rapair has checked my ECU on several occasions and everything checked out. We put the fattest injector in #6. If I remember correctly it was about 1% richer than the other 5. Plus, the majority of the times mine has went down has been at WOT instead of the midrange lean condition that has gotten the majority of the Pro Maxes.

JohnBoy
05-22-2001, 04:14 PM
Have you checked the exaust tuner to make sure it has not come loose. This will cause the lower cylinders to run lean.

Russ
05-23-2001, 07:58 AM
Matt, how old is this motor, and how hard has it been run, and has it been resleeved on #6. Aside from that, you may wish to consider a fuel foaming condition. #6 would normally be the 1st cylinder to feel the effects of this, as foam would be picked up by the 1st injector from where fuel enters the rail. If you answer the above ques, I'll give the next senario. Good luck...

Matt
05-23-2001, 06:58 PM
It's a 96 model that ran great until May of 2000. Since then it has seized up 5 times. Nothing has changed with the motor except for some JSRE exhaust chest work. Rapair put an extra 2% more fuel in up top to compensate, maybe I need more. I'm open to any suggestions.

ODDD1
05-23-2001, 10:00 PM
Matt, are you running water dams on the lower 4 cylinders?
This was done on newer motors to help lower cylinder heat buildup....

Matt
05-24-2001, 08:45 PM
Yes I am running the water dams, with restrictors discs with 5/16" holes, and no poppet valve. If anything it runs too cool. You can leave the back side of your hand on the heads or anywhere on the block all day long after a WOT run. In fact, the last time it let go at 7200 I had the cowling off with a few seconds and it wasn't hot. I'm just about positive it is a fuel or timing condition, but I'm open to any remote suggestions.

Matt

92xb2002t
05-25-2001, 01:01 AM
Matt, I don't know if this will help but many years ago I rebuilt a friends mid 80s 115 inline 6 which had seized #4 which tends to be the lean cyl in that motor. It would never run hot and it persisted to seize up that same cyl. After lowering max timing and fattening the high speed jets in the carb that affected that cyl and rebuilding the motor 3 more times, we found the problem. It was a faulty advance module/idle stabilizer that was over-advancing the timing. There was no meter check to find this problem. My instructor at Merc school had heard of this situation one other time. I removed the black box and the motor is still running to this day. Good Luck

Matt
05-25-2001, 08:10 PM
XB2002,
That sounds like something to check. It's probably something weird like that. Did you replace it with a new one or just take it off? I've checked timing with it disconnected and connected, and there's about 5* difference in max timing. Thanks for the tip.

Matt

92xb2002t
05-26-2001, 12:37 AM
Matt,

I did not replace it. I did adjust the timing close to what it would be with the module connected though.
Good luck