Is this fuel pressure regulator or damper bad?
12-07-2014, 05:05 PM
#1
Three Wheelin'
Thread Starter
Is this fuel pressure regulator or damper bad?
When I started the engine cold, the fuel pressure needle was bouncing all over the place. As the car began to warm up, it settled down, but it's still a little jumpy in the video.
The odd part is, when I rev the engine a little, the needle starts shaking a lot, and starts dropping down to around 1.5 bar (this doesn't come out very clearly in the video unfortunately). I was expecting it to go up a little, and to bounce a lot less.
The test plan simply says it should be 2 bar at idle, and 2.3-2.7 bar with the vacuum line removed. It doesn't mention anything about how stable it should be, or what should happen if you rev the engine. But my understanding of it is, the pressure should go up, to compensate for increased manifold pressure. Mine is not doing that. If I pinch off the return line it does go up well above 4 bar so the pump must be fine.
The odd part is, when I rev the engine a little, the needle starts shaking a lot, and starts dropping down to around 1.5 bar (this doesn't come out very clearly in the video unfortunately). I was expecting it to go up a little, and to bounce a lot less.
The test plan simply says it should be 2 bar at idle, and 2.3-2.7 bar with the vacuum line removed. It doesn't mention anything about how stable it should be, or what should happen if you rev the engine. But my understanding of it is, the pressure should go up, to compensate for increased manifold pressure. Mine is not doing that. If I pinch off the return line it does go up well above 4 bar so the pump must be fine.
12-08-2014, 01:49 AM
#2
Burning Brakes
A better test is to unplug the vac line and see if the pressure goes up, it should be 2.5 bar (36.5 psi) with the vac line off. A little bouncing is normal since the injectors are all triggered together and this sends a shock wave down the fuel line.
12-08-2014, 02:12 PM
#4
...
The odd part is, when I rev the engine a little, the needle starts shaking a lot, and starts dropping down to around 1.5 bar (this doesn't come out very clearly in the video unfortunately). I was expecting it to go up a little, and to bounce a lot less.
The test plan simply says it should be 2 bar at idle, and 2.3-2.7 bar with the vacuum line removed. It doesn't mention anything about how stable it should be, or what should happen if you rev the engine. But my understanding of it is, the pressure should go up, to compensate for increased manifold pressure. Mine is not doing that. If I pinch off the return line it does go up well above 4 bar so the pump must be fine.
...
The odd part is, when I rev the engine a little, the needle starts shaking a lot, and starts dropping down to around 1.5 bar (this doesn't come out very clearly in the video unfortunately). I was expecting it to go up a little, and to bounce a lot less.
The test plan simply says it should be 2 bar at idle, and 2.3-2.7 bar with the vacuum line removed. It doesn't mention anything about how stable it should be, or what should happen if you rev the engine. But my understanding of it is, the pressure should go up, to compensate for increased manifold pressure. Mine is not doing that. If I pinch off the return line it does go up well above 4 bar so the pump must be fine.
...
I replaced everything, the damper and the regulator. Now the fuel pressure goes up to around 2.7 bar when you open the throttle and the car is a joy to drive.
Apart from that, my bad FPR was the culprit for the failed leakdown test.
12-08-2014, 02:15 PM
#5
Three Wheelin'
Thread Starter
below is the behaviour of my bad FPR. There was no difference between vacuum line removed or not. The pressure was the same. But as you can see the pressure went down when you opened up the throttle. That's wrong, no doubt about it.
I replaced everything, the damper and the regulator. Now the fuel pressure goes up to around 2.7 bar when you open the throttle and the car is a joy to drive.
Apart from that, my bad FPR was the culprit for the failed leakdown test.
I replaced everything, the damper and the regulator. Now the fuel pressure goes up to around 2.7 bar when you open the throttle and the car is a joy to drive.
Apart from that, my bad FPR was the culprit for the failed leakdown test.
12-08-2014, 02:25 PM
#6
Yes, the damper should dampen the shock waves triggered by the injectors as Dave W. above explained.
12-09-2014, 12:42 PM
#7
Rennlist Member
If you pressure/vacuum test at the nipple on the damper, and it holds vacuum /pressure, can it still be bad?
My fuel pressure gauge jumps around as well, but I have no obvious signs of a bad damper. Some have said, one should be able to smell gas coming from the damper if it is bad.
I always wondered about this.
My fuel pressure gauge jumps around as well, but I have no obvious signs of a bad damper. Some have said, one should be able to smell gas coming from the damper if it is bad.
I always wondered about this.
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12-09-2014, 10:55 PM
#8
Three Wheelin'
Thread Starter
Good question. I had another old damper lying around so I swapped that in. It didn't seem to make any difference - I still had the fluctuations, and the pressure seems to drop a little overall when I rev it at little. Still it was an old used damper so that doesn't prove anything.
12-09-2014, 11:48 PM
#9
Rennlist Member
By the way, I think the pressure going down a little when reving at idle is normal. You're generally going to have more vacuum at the manifold in such a case, and then that signal will be received at the FPR.