Bad Fuel Pressure Regulator?
08-18-2007, 12:38 AM
#1
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Bad Fuel Pressure Regulator?
I've got a '87 na 944 that shuts down on me after driving a few miles
(under 10), and I'm unable to restart.
It's happened to me 3 times, and the 1st 2 times I had the car towed to a
mechanic that said the car was running fine.
The 3rd time was Wednesday after picking up the car from the mechanic and
driving about 1.5 miles. While trying to start it after the shutdown, I
was able to verify I WAS getting a spark. I installed a DME relay jumper
(clarks-garage) and it did NOT help the
car start which I'm rules out a bad DME relay (replaced in 2002).
I did find that after leaving the car shut down for 5-10 minutes, the car
would start and run for about 2 seconds before shutting down. I repeated
this several times. I unplugged one of the fuel injector plugs and the
car started and I was able to drive the car home (about 7 mi.)
In reading Clark Fletcher's troubleshooting guide
(clarks-garage), the problem seems to be high fuel pressure
due to bad fuel pressure regulator. The only thing that might not fit is
the fact I was able to drive the car 5 miles or so the first two times I
had the problem.
I'm wondering if a new fuel pressure regulator is a sure bet, or do I need
to verify high fuel pressure with a gage & adaptor (I don't have)?
(under 10), and I'm unable to restart.
It's happened to me 3 times, and the 1st 2 times I had the car towed to a
mechanic that said the car was running fine.
The 3rd time was Wednesday after picking up the car from the mechanic and
driving about 1.5 miles. While trying to start it after the shutdown, I
was able to verify I WAS getting a spark. I installed a DME relay jumper
(clarks-garage) and it did NOT help the
car start which I'm rules out a bad DME relay (replaced in 2002).
I did find that after leaving the car shut down for 5-10 minutes, the car
would start and run for about 2 seconds before shutting down. I repeated
this several times. I unplugged one of the fuel injector plugs and the
car started and I was able to drive the car home (about 7 mi.)
In reading Clark Fletcher's troubleshooting guide
(clarks-garage), the problem seems to be high fuel pressure
due to bad fuel pressure regulator. The only thing that might not fit is
the fact I was able to drive the car 5 miles or so the first two times I
had the problem.
I'm wondering if a new fuel pressure regulator is a sure bet, or do I need
to verify high fuel pressure with a gage & adaptor (I don't have)?
08-18-2007, 01:59 AM
#2
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If you remove the vacuum lines to the regulator and damper and fuel comes out, then that's a clue.
A stuck regulator would take a gauge to determine but you can bodge one onto the fuel rail with some hose, hose clamps and adapters. No pressure gauge? Those cheap 1.5" tire gauges they sell by the register at your local auto parts store come in handy. If you take the schrader fitting off they are NPT threaded underneath, and will screw into a piece of fuel line pretty tightly. Add a hose clamp for good measure. If the line is long enough and does not leak, and you keep the gauge higher than the fuel rail, gas will not enter the gauge as the air in the fuel line will buffer it. You can easily check the calibration of the gauge with a tire and a trusted tire gauge. I suggest having a fire extinguisher handy, wearing safety goggles (fuel spray is not good) and have a helper manning the ignition key.
But if you pull those vacuum lines and fuel leaks out where the vacuum line fits, you have found your problem. And check your fuel lines while you are at it.
A stuck regulator would take a gauge to determine but you can bodge one onto the fuel rail with some hose, hose clamps and adapters. No pressure gauge? Those cheap 1.5" tire gauges they sell by the register at your local auto parts store come in handy. If you take the schrader fitting off they are NPT threaded underneath, and will screw into a piece of fuel line pretty tightly. Add a hose clamp for good measure. If the line is long enough and does not leak, and you keep the gauge higher than the fuel rail, gas will not enter the gauge as the air in the fuel line will buffer it. You can easily check the calibration of the gauge with a tire and a trusted tire gauge. I suggest having a fire extinguisher handy, wearing safety goggles (fuel spray is not good) and have a helper manning the ignition key.
But if you pull those vacuum lines and fuel leaks out where the vacuum line fits, you have found your problem. And check your fuel lines while you are at it.
08-18-2007, 08:59 PM
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Jfrahm,
Thanks for the info. I'll check the vacuum line and see about rigging up a cheap pressure gage.
Bearone,
The mechanic left the car idling a lot. He said he drove it, but my guess is not very far for fear of being stranded.
Fuel filter age - Not sure, I haven't replaced it since I bought the car in 2000.
Thanks for the info. I'll check the vacuum line and see about rigging up a cheap pressure gage.
Bearone,
The mechanic left the car idling a lot. He said he drove it, but my guess is not very far for fear of being stranded.
Fuel filter age - Not sure, I haven't replaced it since I bought the car in 2000.
08-20-2007, 09:41 PM
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I checked the fuel pressure tonight, and it checked 38 psig with the engined stopped and fuel pump running (jumpered), and 31-32 psig at idle. This compares with the fuel pressure specifications on Clarks Garage of 36 psig +/- 3, and 29 psig +/-3 respectively. A little high, but within specs.
The vacuum lines on the fuel pressure regulator and the pressure damper were both dry as a bone.
For kicks, I pulled the vacuum hose off of the fuel pressure regulator momentarily while the car was running and the fuel pressure increased to around 40 psig. So now I'm wondering if I might have a vacuum leak. I trace the the vacuum line back and see what looks like chafing residue on the block under the vacuum line. While the car was running, I lifted the vacuum line off of the block, and after few seconds, the fuel pressure skyrocketed to 100 psig and the engine shut off. I tried lifting the vacuum line again, but I didn't get an increase in pressure.
Anyway, I plan to do some disassembly to get a visual on the bottom of the vacuum line and check for a hole. Does it make sense that fuel pressure could go that high with a vacuum leak?
Thanks,
Alan Barbee
The vacuum lines on the fuel pressure regulator and the pressure damper were both dry as a bone.
For kicks, I pulled the vacuum hose off of the fuel pressure regulator momentarily while the car was running and the fuel pressure increased to around 40 psig. So now I'm wondering if I might have a vacuum leak. I trace the the vacuum line back and see what looks like chafing residue on the block under the vacuum line. While the car was running, I lifted the vacuum line off of the block, and after few seconds, the fuel pressure skyrocketed to 100 psig and the engine shut off. I tried lifting the vacuum line again, but I didn't get an increase in pressure.
Anyway, I plan to do some disassembly to get a visual on the bottom of the vacuum line and check for a hole. Does it make sense that fuel pressure could go that high with a vacuum leak?
Thanks,
Alan Barbee
