Tim's 944LS1 track car build!

I don't have any vacuum signal to my fuel pressure regulator. The regulator is at the back near the tank, integral to the fuel filter. The pump runs at a constant 12v triggered, but not varied, by the PCM. The fuel rail itself is returnless. It has a damper deal in it but no vacuum based pressure regulation.

Tim, is your setup the same?

Rich

You may have to test the fuel pressure at the engine then to make sure it isn't either leaning out of running too rich at WOT. Even if it won't tell you if it is the regulator or the pump, at least you will be able to narrow it down to the fueling rather then ignition.

Have you taken a look inside the tank itself to see if there is garbage in it that is getting pulled onto the screen from time to time? The new bio fuel that we are forced to get at the pumps has caused hell with some fuel systems from the Mini's to the Super Duty trucks. Check for debris and since you have it off you could change the pickup screen on it.

I think he already said he did that.

944-LT1 wrote:

Lemming wrote:(I have a lift and scales, that means lots of friends!).

You Bet!

I'm 85% sure I'm going to buying a lift this year. 4 post, 2 post, scissor, not sure yet.

Also, hey M! Glad to see you here. Been awhile for me. <--just a shout out.

I'd love a 4 post lift, would make fitting 3 cars and my motorcycle in the garage a lot easier.

I've discovered that the lift is the cheap part though, installation, electrical, garage door etc will cost as much as the lift itself.

Wish I didn't have so many other house projects that take precedence over improving the garage...

Spent the weekend trying to get her to run at Barber, but no go. I've got good fuel to the rail (when stationary and revving) but when it cuts out if goes lean (as indicated by spark plug reading). Had a code reader but not throwing any codes. I hot wired the fuel pump to make sure that there was not an issue with the relay or computer, that did not help.

Will get it to my shop this week. I think it's time for me to invest in an HPtuner setup so that I can monitor everything myself. If I had one, this thing would likely be fixed by now.

Were any OBD-II DTC trouble codes turned off which would have been of some help if they were left turned on. Can anyone recommend which codes would help in any/all engine related troubleshooting and have those turned back on? (Of course, some sensors may not been present and would not be turned back on.)

At least you installed the DTC plug for a code reader which makes good sense.

btw…was the crankshaft removed during the rebuild?

I'm not sure what codes were turned off but will find out this week. I know it reports errors for fan relays, MIL, and transmission, not of which are hooked up.

Crankshaft was not removed, nor was anything on the front of the engine. I pulled heads, oil pan, and pistons. Engine remained in car.

What have you done for the fuel tank ventilation system? Maybe that's plugged-up and when you go hard it's building vacuum in the tank and reducing fuel flow. You could try running with the gas cap off just as a test.

Rich

Lemming wrote:Crankshaft was not removed, nor was anything on the front of the engine. I pulled heads, oil pan, and pistons.

The reason I asked was because it is important to change the $15 exciter ring on the Gen III whenever the crank is taken out. Read:

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On my project I am duplicating the usual engine sensors to monitor for both the 944 analog instruments as well as the PCM’s digital requirements and will wire up the MIL to a ‘check engine’ light whenever an important code is thrown.

That’s why I too need a list of the recommended error codes to keep. Let us know what you find out…your effort’s will save us all a lot of grief.

Rich L. wrote:What have you done for the fuel tank ventilation system? Maybe that's plugged-up and when you go hard it's building vacuum in the tank and reducing fuel flow. You could try running with the gas cap off just as a test.

Rich

Took care of that when this chassis was holding a supercharged 968 engine. None then less, I did check the tank at the track and that not it (but good suggestion).

I'm going to pick up an HPtuner Pro so that I can log sessions on all components when things like this happen. It sucks to spend 1K on race entry fees, hotels, gas, etc., and then not get to drive. Plus, I can't always get my car on the dyno quickly as they have been swamped trying to get cars ready for the 2013 race season.

EDIT: HP tuner Pro is on the way.

Off to the dyno on Thursday night to try and get the car to fail while being monitored. I got my HP tuner set up and working but the car runs fine revving it in the driveway, so problem may still be there. My HOA would hang me out to dry if I took the car through the neighborhood to test it.

I've checked just about everything I can think of. Tonight I changed the way the fuel pump is wired. Since the battery is located in the spare tire well, I decided to run power straight from the battery to the pump (and yes, there is a 30 amp fuse and relay installed in the line, but triggered from the painless switched fuse box in the front). Now there is very little chance that there is a significant drop in power to the pump.

Car was on the dyno last night, it was knocking but that is likely due to a bad knock sensor which was pulling 4 degrees of timing out of the car around 3k rpms. Will replace both knock sensors today after work. We could not get the car to shut down like it has done the last two weekend on the track. So not sure if I fixed that latter problem or not

Huh, how odd. Can you haul it out of town to romp on it a bit on a country road? Track time and dyno time are both expensive ways to test.

Rich

Rich L. wrote:Huh, how odd. Can you haul it out of town to romp on it a bit on a country road? Track time and dyno time are both expensive ways to test.

Rich

Just changed my plans, not going to haul the car over 6 hours to Roebling Road next weekend, instead I can instruct here at Barber (20 min from home).

Lemming wrote:Car was on the dyno last night, it was knocking but that is likely due to a bad knock sensor which was pulling 4 degrees of timing out of the car around 3k rpms. Will replace both knock sensors today after work. We could not get the car to shut down like it has done the last two weekend on the track. So not sure if I fixed that latter problem or not

Make sure you replace the harness for the knock sensors as well as the knock sensors or you will be right back in there. Runs about $35 bucks. On the newer chevy motors, almost all knock sensor issues are due to the stupid harness (as well as water accumulating in the rear knock sensor port, not likely an issue if you are is garaged/not driven on the street in the rain most of the time). I replace a lot of them on 5.3 and 6.0 truck motors.

Porschedoc wrote:Make sure you replace the harness for the knock sensors as well as the knock sensors or you will be right back in there. Runs about $35 bucks. On the newer chevy motors, almost all knock sensor issues are due to the stupid harness (as well as water accumulating in the rear knock sensor port, not likely an issue if you are is garaged/not driven on the street in the rain most of the time). I replace a lot of them on 5.3 and 6.0 truck motors.

I replace both sensors as well as one plastic harness (the other was replaced when 1.5 years ago). Took it for a quick ride through the hood, no knocking or error codes. Hope all is well, I'll find out this coming weekend at Barber.

Went to a different dyno with a great tuner last night. We were still getting a knock code but there was no knocking. He thinks the knock is noise from the car and is not worried about it at all, so we took knock out of the equation for the testing. Got very nice repeatable curves but still not at the power that I need to be competitive against the vettes in ST2. He is going to spec me out a cam, springs, push rods, and injectors with the goal of creating a torque monster that has rwhp capped at 350. Of course there will be other tunes where that HP is allowed to run free when I'm not limited by my race class.

Last weekend was yet another weekend of outlaps only The car dies after 1/2 of a lap, if you then shut the power off (including computer), it starts right up and runs like a champ for another 1/2 lap. We were convinced that it was electronic. Luckily I had a tuner friend with me and we tried everything, new program, new computer, wiggled wires, etc, nothing. We then went back to fuel and the car failed with a pressure gauge on it, this showed that pressure was way down when revved (60 psi at idle and up to 1/3 throttle- above that it would drop to 20psi). We checked voltage and amperage to the pump, that is just fine. We then hotwired the fuel pump, got the car to go into fail mode, shut the car off (with pump still running), then restarted. Low and behold, the problem was still there, showing that it has nothing to do with the computer or harness.

So, what the hell is happening? Remember from previous posts, that after this began, I have installed a new fuel pump as well as the c5 filter/regulator, so I doubt that is the issue. I was thinking that possibly the rubber line from the pump to the filter was getting kinked and that it remained so until you too pressure off of it (hence why the car restarts so easily). But when I removed it, it appears fine? The hose from the tank to the fuel pump appears fine, we looked at it in fail mode and it was not kinked.

I'm also wondering about the pressure regulator on the stock LS1 fuel rail, could that be failing in some manner?

And yes, I've looked into the drained tank on three different occasions now, and there is nothing out of the ordinary. Currently I do not even have an intank fuel filter installed.

Thoughts?

Lemming wrote: The hose from the tank to the fuel pump appears fine, we looked at it in fail mode and it was not kinked.

Any chance this line is collapsing internally under load?

Okay. So everything is okay until flow is high for a short period of time. Then a restriction develops which remains until flow is stopped completely. And then it's okay again immediately. Sure sounds like a blockage of some kind in a line. I'd start with that line from tank to pump as it's short and easy to change with some new generic fuel hose.

The deal on the fuel rail is a pressure damper. It just smooths out any pulsation generated by the pump. I don't think it could fail in any way that would cause what you're seeing.

Rich

944convert wrote: Any chance this line is collapsing internally under load?

This is a real consideration, especially if the line is the original 944 line or a line not rated for 60psi or higher. Happens on old rubber brake lines also.

Pull the spring clip and inspect the diaphragm on the damper to make sure there are no rips. Depressurize the line first.

I know that a lot of people run the OE fuel rail and combo filter/regulator, but I decided to keep the OE return system with an adjustable pressure regulator with gauge on the return line. This does away with the damper and filter/regulator which could create problems and makes trouble shooting easy. For me its either the fuel pump or regulator so I keep a spare pump and diaphragm in parts bin.

Running without the gas cap on is also a great idea. I had a cut out problem early on and found the rubber vent hose between the hard line under the car and fuel tank had melted shut (exhaust pointing in the wrong direction, doh). I figured it out when I opened the gas cap and there was this huge sucking sound coming from the tank.

What about the fuel pump?? If it is going bad, putting it under stress might be causing the motor to bind. If it a bosch unit and the OE check valve (brass nose piece on outlet) is still in place make sure it is not stuck.

Probably not much useful info here . . . Sorry.

I don't think it's the line from tank to pump, that section is only 2" long and then goes to a 150 degree hare fitting to the pump. I did replace that 2" piece after the first weekend of problems. I guess it wouldn't hurt to replace with braided line.

The pump is new and is a walbro 392. After I had the problem the first weekend, I replace it with a brand new 392. I will check the "check" valve and my just drill it out.

The line from the pump to the c5 filter/regulator is the original porsche part. It appears to be in excellent condition, but I'm planning on replacing it. I really don't want to change the setup to a return system (at the rail), and since it worked fine for the first 1.5 years, it should work again after I find the hickup.

I pulled the rail damper and it looks fine inside.

I did think about gas tank vacuum or pressure while at the track, so I pulled the cap during a fail and there was no pressure difference.

What brand of fuel filter/regulator are you using?

First one I used was a Wix, the one I put into the car after the first weekend that I had problems is a NAPA gold unit.