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Need Help with fuel pressure

I am trying to trouble shoot the car being overly rich with throttle imput and too lean while just idling. It will stall out idling when warm.

I put gauges on the CIS. My system pressure was saying 86psi. When I would do a cold test the needle would drop quickly to about 25psi then shoot right back up to 86 and hold.
When I plug the wur in there were no changes to the pressure.

At first I thought it was the wur. It wasn't the element inside, that would warm up and the resistance was in spec for the strip. I checked the screen, cleaned the wur and reinstalled. Still no difference.

I finally purchased a rebuilt wur (not adjustable) car is mostly stock albeit SC cams and a K27hf turbo. I ran the gauge test again. Exactly the same results.

Is it possible the fuel return line could be plugged? I blew air through the return line and I could hear it entering the gas tank. Could it be the poppet valve. Doesn't that regulate system pressure as far as what bleeds off to the return line?

I removed it and it is clear of any obstructions.



I don't want to take this to a shop, I would prefer to work through it and learn. Any help would be appreciated. I would like to take this car to MO for Porsche Polooza in October, but I need to have confidence I 'm not going to get stuck or worse, damage the motor.


Thank you,

John
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John- I blame and thank the longhood boys of Austin
-84 911 Carrera w/ 930 t/p,efi'd,dizzy free,HFS turbo, 78 930 RoW no option sunroof coupe, 64 Corvette roadster, 71 911T, 73 911E, 67 Bronco survivor. 71 FJ40, 95 M3 (for sale)
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Last edited by sundevil64; 09-12-2011 at 03:31 PM.. Reason: add text and pic
Old 09-12-2011, 02:36 PM
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Rookie, but I'll try to help...

I am not sure, based on your description, I know exactly what you did and how.

The pressures your recorded, did you compare those to the factory specs?

I usually use bar units, but I think the 25psi would be too low for ccp...? Depending on environmental conditions at the time of testing. Check the fac. Manual.

Just a wild guess. Could it be CO screw that is off for idle, causing a lean condition, and cp being too low causing the metering plate to drop too easy while "bleeping" the throttle resulting in a rich condition???

I bet expert opinion will be soon

Just my 2cents

Good luck
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Old 09-12-2011, 05:12 PM
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Has your car been running fine up to this point, then suddenly these symptoms? Could be you've got a problem with one of the fuel pumps not running. That could explain the lower system pressure and rich when running beyond idle. Could be that, maybe not. Confirm that both pumps are running, you need to get your system pressure where it belongs. And slap in a new fuel filter, just in case it's plugged with sludge.
I'm not too clear on your cold CP's. They should be around the low 2.? bar (would have to look up the specs), then rise within a couple minutes of plugging the power connection back in. Just because the resistance of the internal heating element is ok, doesn't mean it's heating up. It's fed power via the rear fuel pump relay....could be a common problem. Check to see that you're getting voltage at the connection (pumps must be running).
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Old 09-12-2011, 06:14 PM
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jsveb,

I'll check the CO screw, that could be part of the problem. If I recall correctly, the fact manual says I should be between 2-4 bar.

Mark H,

The car has a specked history. The motor had been pulled and put in another 86 by the PO, then put back in when the PO decided to sell the 78 930 (which is the car we are currently talking about). We couldn't get it to start. It was not getting any fuel. I changed the accumulator and the filter. Then the supply line coming off the rear pump balloon and burst indicating a blockage somewhere. I replaced the fuel pump with another from my narrow body turbo project to test it and replaced the lines. I got the car started. I tinkered with the idle and the mixture until I could get it to run and idle smoothly. I drove it around the block a couple of time with an LM-1 attached and everything seemed fine, a little rich, but fine. Then it started acting up. It wouldn't idle for long periods with out stalling and with throttle input it would over richen to the 8 and 7 range. So I decided to get some CIS gauges and check pressures. I thought my wur was fired because it wasn't bleeding off the pressure.

As far as the wur, I not only check resistance I put my finger to the coating and it was heating up. At any rate I acquired a rebuilt one (not adustable) and have installed it with the same results. So It would tell me this isn't the wur. I hate just replacing parts. Everything was telling me the wur was shot.This wur (054) has a vacuum activated fuel enrichment, should I apply vacuum to it?

I have been thinking about putting the original rear fuel pump back in to see what I get. I didn't know if I should pull a shim from the poppet valve to lower the pressure. There is only one left.

John
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-84 911 Carrera w/ 930 t/p,efi'd,dizzy free,HFS turbo, 78 930 RoW no option sunroof coupe, 64 Corvette roadster, 71 911T, 73 911E, 67 Bronco survivor. 71 FJ40, 95 M3 (for sale)
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Old 09-13-2011, 03:52 AM
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Quote:
Originally Posted by sundevil64 View Post
jsveb,

I'll check the CO screw, that could be part of the problem. If I recall correctly, the fact manual says I should be between 2-4 bar.

Mark H,

The car has a specked history. The motor had been pulled and put in another 86 by the PO, then put back in when the PO decided to sell the 78 930 (which is the car we are currently talking about). We couldn't get it to start. It was not getting any fuel. I changed the accumulator and the filter. Then the supply line coming off the rear pump balloon and burst indicating a blockage somewhere. I replaced the fuel pump with another from my narrow body turbo project to test it and replaced the lines. I got the car started. I tinkered with the idle and the mixture until I could get it to run and idle smoothly. I drove it around the block a couple of time with an LM-1 attached and everything seemed fine, a little rich, but fine. Then it started acting up. It wouldn't idle for long periods with out stalling and with throttle input it would over richen to the 8 and 7 range. So I decided to get some CIS gauges and check pressures. I thought my wur was fired because it wasn't bleeding off the pressure.

As far as the wur, I not only check resistance I put my finger to the coating and it was heating up. At any rate I acquired a rebuilt one (not adustable) and have installed it with the same results. So It would tell me this isn't the wur. I hate just replacing parts. Everything was telling me the wur was shot.This wur (054) has a vacuum activated fuel enrichment, should I apply vacuum to it?

I have been thinking about putting the original rear fuel pump back in to see what I get. I didn't know if I should pull a shim from the poppet valve to lower the pressure. There is only one left.

John
Hmmm....a challenging one for sure. Some thoughts: Your system pressue is too low at 86. Should be a good 10 psi higher than that, which would help your overrich condition. Install another shim to the poppet. Is this because of your fuel pump? Could be.

As far as the vacuum operated WUR, I think I would not let it see any vacuum. Chances are your old WUR was fine.

The funny thing is that you got her to run sorta-OK by changing out the fuel pump, but still it may not be the correct pump and is contributing to your low fuel pressure. With that low pressure, when you step on the gas there isn't enough pressure resistance to keep the metering plate arm from overdeflecting and injecting too much fuel. Get your system pressure up, then go from there.

Hopefully your fuel distributor isn't having other internal issues. If you can get her to run well enough for a drive, it would be good to burn a bottle of Techron through a tank of gas. The thing just might be all gummed up inside.
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Old 09-13-2011, 04:56 AM
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Quote:
Originally Posted by sundevil64 View Post
I put gauges on the CIS. My system pressure was saying 86psi.I removed it and it is clear of any obstructions.
Where do you put gauges to check? According manual? If so, system pressure should be 87 to 97psi, if you adjust, then 90 to 93psi

What I miss on your pics are the shims (there are always 3 of them behind the spring)

PS: System pressure should stay always the same. valve is last in line
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Last edited by proffighter; 09-13-2011 at 06:12 AM..
Old 09-13-2011, 06:06 AM
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I'm guessing you have a black cast iron euro fuel head on there because you mentioned it is a '78 and not the aluminum lambda fuel head from a 1986 or later USA car.

My car is an '87 and I've used the stock USA fuel head, 2 different CIS flowtech modified USA fuel heads, and a stock black euro fuel head. I have the CIS opressure gauge and checked all of them while they were installed on the car.

The aluminum lambda heads system pressure runs in the high 90's to 100psi and the black euro fuel head system pressure I had ran in the high 80's similar to yours. I thought that was low at first but then learned thats in the normal range for a euro fuel head so I don't think your fuel system pressure is too low.. but maybe it is.

The euro head is a little different than a 1986 on USA aluminum lambda head. It has a stiff stainless steel metering diaphram and no lambda system with frequency valve like a USA fuel head, and normal system fuel pressure is in the high 80's for them.

The USA head has a more flexable metering diaphram in between the upper and lower diferential pressure chambers and a lambda system returning fuel to the tank from the lower chamber for emission lean AFR control and system pressure is around 10 psi higher for them.
Pelican sell parts for the fuel head system fuel pressure regulator you're calling a poppet valve but I think yours is OK. The orings on it look good and it's clean. They don't all have 3 shims under the spring, some have one thick one or 2 or 3 thinner shims stacked together if that got the static sytem fuel pressure set correctly 33 years ago.
Pelican Parts - Product Information: 928-110-920-01-M14

Your fuel head may need cleaning and rebuilding inside. Those euro fuel heads rust in the bottom of the lower differential pressure chambers if water gets in there and that can clog things up in the thin fuel passage ways and metering orifices and fine mesh fuel screens inside. The rubber o rings around the control plunger steel cylinder can also disintegrate over time and clog fuel flow.

Some fuel additives can accelerate the 30+ year old orings breaking down. It can also loosen up old accumulated dirt or varnish and let it move some where else where it will cause fuel flow problems.

You can do an injector flow test into 6 seperate plastic small water bottles with and with out injectors on the ends of the lines to get an idea whats going on there.
Alot of things can cause problems in an old mechanical injection system like CIS.

Last edited by JFairman; 09-13-2011 at 07:20 AM..
Old 09-13-2011, 07:11 AM
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Off the cuff it sounds like your fuel head has had a stroke. You can try flushing it out.
The -054 does not enrich with vac but rather boost, same as the -112 or -153.
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Old 09-13-2011, 07:56 PM
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according manual there have ALWAYS to be 3 shims:
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Old 09-13-2011, 10:16 PM
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Old 09-13-2011, 10:19 PM
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Thank you guys for the ideas, I'm grateful to get some input on possibilities.

When I could not get the car to initially start after bursting the fuel line I decided to check all the fuel lines and replaced one. The other have recently been replaced with factory lines. I had also heard about how the FH can get gummed up the the piston will stick or cause other problems. So, I took the FH off and removed the piston (carefully) and inspected it. It was actually pretty clean there was an ever so slight indication of gumming. I soaked it and it came right off. I also soaked the FH. I removed the fuel lines to the injectors of course and did find two filters in one port, indicating either someone at Bosch messed up or someone had been in there. The screens were otherwise clean. I put one screen/filter back in each fuel port, put the pin back in (carefully) everything seem to just move smoothly. There were no indications of rust at all no even on the fuel head exterior. I reinstalled the FH with new copper washers. It then started after it was all together.

The problems have recently arrived as I drove it around more. It was stalling out. When it would stall at idle the afr would climb into the high teen range, it would stumble slightly and stall.

I did install a shim that is exactly identical to the shim (originally there was one, i think). Any way not there are two and the pressure is around 95.

When I read the factory manual (page 20-4) it says pressure immediately after the rear fuel pump should be 2-4bar(28.5-57ishpsi). If under 2 bar replace front fuel pump, if over 4 bar replace the rear fuel pump.

Is there something that increases the pressure after the fuel pump?

Also, that's the system pressure with the valve closed on the gauges. When I "open" the valve for fuel to go to the wur shouldn't pressure drop to around 2.3-2.5 bar given the warm ambient temperatures here in TX?
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Old 09-14-2011, 02:47 AM
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Fuel head

Quote:
Originally Posted by RarlyL8 View Post
Off the cuff it sounds like your fuel head has had a stroke. You can try flushing it out.
The -054 does not enrich with vac but rather boost, same as the -112 or -153.
Brian,

Is there a way I can verify this? I thought the wur was bad, but after changing that out I still have the same results. It can get expensive changing parts out.

John
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-84 911 Carrera w/ 930 t/p,efi'd,dizzy free,HFS turbo, 78 930 RoW no option sunroof coupe, 64 Corvette roadster, 71 911T, 73 911E, 67 Bronco survivor. 71 FJ40, 95 M3 (for sale)
"Illegitimi non carborundum"
Old 09-14-2011, 02:48 AM
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Hmm a tricky situation to say the least. Unfortunately trial and error is usually the way to find the culprit(s).

Check your flow rates from the pumps (per the manual) and injectors. If they are correct and you have tried different WURs (correct pressures) with the same bad results that points to the fuel head. Unfortunately due to years of differing conditions these things are prone to variations in problems and solutions.

I bet not all fuel heads have 3 shims. Mine had none and I had to add and remove many before finding a nice balance. Too high system pressure resulted in 'run-on' (dieseling) in my case. The manual is a 'guide' for settings and pressures and slight adjustments can have large differences.

Unfortunately you would be better to get an adjustable WUR. Adjust your pressures and find exactly where your car is happy. You may be able to raise system pressure and lower control pressure or vice-versa and find it runs fine. Otherwise a fuel head rebuild is on the cards.

I have found by accident mine is running about exactly the same cruise and idle afrs (I don't know if this is normal - I thought a richer idle would be better). I still have an enrichment problem under boost even tho I have an RPM solenoid active but anyhoo thats a whole nother episode.

Good luck and post your findings!
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Last edited by Helmsy; 09-16-2011 at 06:07 AM..
Old 09-16-2011, 06:04 AM
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yeah, not all of the fuel pressure regulators had the exact same shim pack... i don't care what a scan of a piece of paper say's, i've removed a bunch of them in the last few years and one or two of them had 2 shims, a thick one and a thin one to get the correct system pressure.
Old 09-16-2011, 06:28 AM
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I added a shim and now the pressure is at 98psi. That's high. I pulled the fuel pump that I have installed from my other narrow body that was converted by a shop to verify the number versus the original that was in the 930. They are the same and correct number. The old one worked correctly, so I installed that and that gives me an extra as I'm converting my narrow body turbo'd car to EFI with a 3.2 intake. That's a chore.

Anyway, I'm going to remove all the shims when I get time and see what my pressures are. I do have a FH on the way to test, thanks to the courtesy of another pelican member. If it works then there is obviously a problem with the FH which I suspect, but want to be 90% sure.

This has gotten me to start thinking about converting this car to efi, but utilizing injector blocks so I don't have to fab up an intercooler. Actually, so my buddy doesn't have to fab up an intercooler for me...

I'll post my findings as I go. Hopefully if someone else runs into this problem they can avoid some work and expense.

Also I converted my old wur to adjustable, but I have to get a roll pin to prevent the plug from potentially rotating. I think it may have been fine as mentioned by others in this thread.
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-84 911 Carrera w/ 930 t/p,efi'd,dizzy free,HFS turbo, 78 930 RoW no option sunroof coupe, 64 Corvette roadster, 71 911T, 73 911E, 67 Bronco survivor. 71 FJ40, 95 M3 (for sale)
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Old 09-16-2011, 06:40 AM
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Maybe it's a bit confusing here, but everyone talks about shims, removed one, add one, two or none found etc...

But does all know that there are different thicknesses there? So there have to be 3 and when pressure should be changed a thicker or thinner will be fitted instead of another. Of course, one thick can replace two thins, but that's not what Porsche recommended in that "scanned piece of paper". I think they had good reasons for choosing this method.

But for the problem here it's not that important
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Old 09-16-2011, 06:53 AM
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