M30 Fuel pressure - SOLVED!

[Corner Carver]

I just want to verify that I should be seeing 43psi at my fuel rail and if I am only seeing 35 psi then there is a problem. I swapped out my 3.0BAR FPR with a known good one and pressure was the same so it is probably a fuel pump right?

My question is: If the intank pump is dead would I see a drop in pressure such as I am seeing, or does the inline pump provide all nessesary pressure and the symptoms I have indicate a worn inline pump?

[turbodan]

43psi with the vacuum line disconnected, and only if its supposed to be a 3 bar system.

The FPR is probably fine. The in tank pump wont cause a drop in fuel pressure. The main pump supplies far more than is needed to maintain pressure, and the FPR routes the excess back to the tank.

[Corner Carver]

Thanks Dan, yes it is 43psi with the vacuum line disconnected. The issue I am trying to solve is a complete cut out / hesitation at 3500 rpm. It only happens under load and only happens at 3500rpm, runs like butter otherwise. I have swapped out known good ECU's (3 to be exact) and there was no change. I just refreshed the topend and this did not occur before the rebuild.

What am I missing?

[DJM1986-5]

I had a similar issue - bad miss or flat spot around 3700 and then again further up on my 533. I had a cam access plate leaking (behind the head on the firewall side) that would leave a spot of oil....I fixed that last weekend and it resolved most of the flat spot in acceleration and smoothed the idle. Nothing else was touched ???

I can only imagine that the negative on vacuum caused other issues as most vacuum leaks do. The vacuum pull from my under dash temp sensor is now noticeably stronger. Go figure.

[turbodan]

Vacuum leaks are a possibility.

[Scottinva]

It's suprising how many vacuum leak problems people seem to be having. These vehicles have an extremely small amount of vacuum lines, and rubber boots to cause leaks.

[Corner Carver]

I have searched high and low for vacuum leaks. All small gauge vacuum hoses are new, intake boot is new, IAC valve hose is new. I would like to use a smoke machine to see any are visible that way.

I had a similar issue - bad miss or flat spot around 3700 and then again further up on my 533. I had a cam access plate leaking (behind the head on the firewall side) that would leave a spot of oil....I fixed that last weekend and it resolved most of the flat spot in acceleration and smoothed the idle. Nothing else was touched ???

I don't think it is the cam access cover plate but I will check . My issue is different than yours in that it is not a flatspot it is a complete cut out, it will not go above 3500.

It screams lean condition problem but I am at a loss for the cause. I have done a lot of searching here in the last couple of days and have found similar issue but nothing that is just like this.

[mooseheadm5]

That would be some pretty important info, there. It was not clear that it would not rev under load past 3500. That would not be caused by a small vacuum leak.

Check fuel pressure while driving. It could be that the fuel pump cannot provide enough fuel under load. I have seen it before. Fuel pressure was fine at idle and revving with no load but pretty much went to 0 above a certain engine speed/load.

[Corner Carver]

That would be some pretty important info, there. It was not clear that it would not rev under load past 3500. That would not be caused by a small vacuum leak.

Check fuel pressure while driving. It could be that the fuel pump cannot provide enough fuel under load. I have seen it before. Fuel pressure was fine at idle and revving with no load but pretty much went to 0 above a certain engine speed/load.

Hmmm... that is interesting, what was the cause of this, just a bad fuel pump? And how would you monitor fuel pressure while driving without an in cabin pressure gauge?

[Scottinva]

There is a pressure test which most people are fimiliar with, but you can also test fuel volume. The pump may be capable of producing the pressure, but not volume.

[Jeremy]

Double check the cam timing. One tooth off in one direction causes valves to contact pistons, one tooth off in the other direction causes symptoms similar to what you're experiencing.

Jeremy

[mooseheadm5]

You use a longer hose and put the pressure gauge under the windshield wiper. I have done it many times. Doesn't hurt to check Jeremy's suggestion, either.

[Corner Carver]

Double check the cam timing. One tooth off in one direction causes valves to contact pistons, one tooth off in the other direction causes symptoms similar to what you're experiencing.

Jeremy

I suppose it is possible that it is one tooth off. I guess my Sunday will consist of checking my cam timing and if that is the case I will be removing my timing covers. What a bummer. all that work just to go back in and do it again. Oh well, chock it up to experience.

Just for good measure I will do Mooseheads suggestion on Saturday and if all goes well I will be taking a Sunday drive on Sunday.

Thanks for the help, I will update you as soon as I know something

[Corner Carver]

Verified cam timing is correct. I am now swapping out a known good fuel pump.

If this doesn't work I remain stumped. Any more suggestions?

[Corner Carver]

SOLVED!

I swapped out my fuel rail, injectors and all, from a spare engine and she runs good now!

I just put new O-rings on the other injectors but they where a harder durometer material like urethane not soft like rubber. I believe air was getting by them at the higher rpm's and I was experiencing a similar situation as CSBolger in this thread.

http://www.mye28.com/viewtopic.php?t=70 ... ht=bucking

Difference was he had disintegrating O-rings and I had O-rings that were too small.

[CSBolger]

Nice!

[BRRV]

Beat me to it. I also had the same hesitation at full throttle, chased it for years - finally solved it after going through the fuel system and, as a last resort, had my injectors rebuilt. It was night and day, and I'm a believer in the idea that these injectors probably need to be serviced at least every 100K miles.

Pintles are fragile, too, and the o-rings do develop leaks, also part of the injector overhaul. I use Redline SI1 all the time now, which, with rebuilt injectors, has helped keep this from coming back.

[joeuser999]

43psi with the vacuum line disconnected, and only if its supposed to be a 3 bar system.

The FPR is probably fine. The in tank pump wont cause a drop in fuel pressure. The main pump supplies far more than is needed to maintain pressure, and the FPR routes the excess back to the tank.

Seeking some clarity on this one... asuming the we are referring to the vacuum line on the Fuel Pressure regulator?

[Shawn D.]

43psi with the vacuum line disconnected, and only if its supposed to be a 3 bar system.

The FPR is probably fine. The in tank pump wont cause a drop in fuel pressure. The main pump supplies far more than is needed to maintain pressure, and the FPR routes the excess back to the tank.

Seeking some clarity on this one... asuming the we are referring to the vacuum line on the Fuel Pressure regulator?

Context, dude. Yes, it is the FPR vacuum line.

[joeuser999]

Seeking some clarity on this one... asuming the we are referring to the vacuum line on the Fuel Pressure regulator?

Context, dude. Yes, it is the FPR vacuum line.