Cutting out at idle

[PodOne]

Hi folks

Looking for some pointers as to the current issue.

The car has covered over 500miles and after a decent run today with no issues or prior I thought it was time to see if I could make the idle a little more evenly as she was oscillating between 600 - 1000 rpm ( I accept they are always bit lumpy) and improve the pick up on accelerating esp in 2nd which after 3000rpm she goes well and not too bad in 3rd & 4th. Tank 50% full of fresh fuel. The whole PI system was refurbished by Neil Ferguson and is running a Bosch pump to an original PRV all fed from new Ali tank with a 10mm outlet.

So Inlet manifold off and air flow meter to balance the throttle bodies all with 0.5 (2.5 - 3.0). During the process the car stalled and refused to start the fuel pump note was more shrill than normal. Switch off and left it for around 60sec and she fired up and ran awhile then stalled again same shrill sound from pump. Connected fuel pressure gauge at MU measured 108-110 psi with key on. She fired ran and then same shrill sound and the gauge measures 30-40 psi and oscillating then stalled again.

Pic and vid attached.

No expert with PI but there's no point trying to adjust the throttle bodies until this issue is sorted.

My thoughts is it the dreaded cavitation but had no previous problems driving her or is the PRV sticking?

Any help and solutions appreciated.

Thanks

Andy

 

[roy53]

I would look for some restriction in the supply to the pump.

Roy

[Mike C]

Is the tank venting properly ? Open the cap and see if things improve.

Maybe the run heated the fuel so much it's boiling in the pump suction line. In this case it will improve when the tank cools down.

Where is the pressure gauge tapping? The gauge is not showing 108 psi.

 

[PodOne]

1 hour ago, Mike C said:

Is the tank venting properly ? Open the cap and see if things improve.

Maybe the run heated the fuel so much it's boiling in the pump suction line. In this case it will improve when the tank cools down.

Where is the pressure gauge tapping? The gauge is not showing 108 psi.

 

Hi Mike

I blew though the return from the MU to tank when the MU was off to replace the seal between the two halves of the MU. (forgot the name). On removing the cap there was no vacuum so guess its venting ok.

The gauge is tapped into the feed just as it enters the MU. Ive no picture of the gauge but it does read 108-110 psi prior to developing the issue.

I'm going to see what she reads tomorrow from cold and physically check the fuel level in the tank as although the fuel gauge reads 50% I wonder if it's a true reading hence fuel starvation. I'd just returned following a blast down the motorway so she was nice and hot. On putting my hand on the fuel pump however it was fairly cool.

Roy the feed/returns are all new if it was a restricted anywhere I'd expect the issue to be worse while driving?

Thanks so far.

Andy  

[JohnC]

I had similar symptoms about 30 years ago. Turned out to be a small piece of plastic bag which was blocking the intake to the fuel filter. No idea how it got there. Anyway, as Roy said, it sounds like a restriction in your fuel supply, which is causing the pump to cavitate. Do report back once you've fixed the problem.

Cheers,
John

[Mike C]

Pump cavitating or PRV sticking at full bypass?

[Waldi]

Hi Andy,

to me it sounds as the pump is cavitating.

This can be from either a restriction in the inlet line to the pump (most likely), or very high flow when the PRV is stuck open (less likely).

Above possibilities are possible causes, maybe also check for a collapsed or kinked inlet hose.

My next step would then be:
The pump will draw around 10A (depending on which Bosch type) so most multimeters can only measure that for a very short time, but it would be nice to measure the current at least when running normal to see if the current reading matches the Bosch graph of your pump-type (@108 psi). 

And finally (because not the nicest job):
If you have a valve at the tank outlet it would be good to decouple the suction line at the pump and measure flow for say 60 sec (but that is a messy job).

You will find it, we all know:)

Waldi

[roy53]

Do you have a pre pump filter ?

When driving the fuel is swishing about. When standing still a particle can settle to the bottom of the tank or where ever and settle .

When the  new pipes were fitted a small piece of rubber from cutting may have been washed through. Check in the pump inlet.

Roy

Edited April 7 by roy53
miss type

[PodOne]

Thanks all

There is no pre filter to the pump.

The filter is after the pump maybe this is something to think about adding but I understand there are lots of cars without a pre filter.

I'll report back when I have done some further investigations.

Andy

Edited April 7 by PodOne
More info

[Neil Ferguson]

Sounds like fuel station 

[JohnC]

30 minutes ago, Neil Ferguson said:

Sounds like fuel station 

Don't you love autocorrect? I'm pretty sure you mean "starvation " 

Andy, try running the engine with the filler cap open. If that doesn't fix the problem (and I'm betting it won't as you haven't mentioned changing anything in that area), then you have something in the feed to the pump. It's just possible the PRV is at fault, but that would be permanent, and it sounds like you can at least start the engine. There's a toenail clipping, or a cockroach, or a small plastic soldier, or maybe even a bit of dirt in the line. Please provide photographs when you find it.

Good luck,
John

[Neil Ferguson]

Technology 

[Mk2 Chopper]

The sound gives you the clue plus loss of pressure, I'm also betting its the inlet side of the pump causing the issue.

There should be definitely be a pre pump filter, more so than post pump filter. 

Gareth

[PodOne]

Hi all

I thought I would update this just in case it might help someone else.

For the clarity the system is all new or reconditioned as follows Ali tank -- 10mm outlet -- 10mm fuel tap -- Pre filter -- Pump -- MU -- PRV -- Fuel Cooler -- Back to tank along with MU return.

Work done.

1) Tank out emptied and checked for **** - none found and both returns to the tank were clear

2) Fuel tap checked its 10mm ID no restriction

3) From tap to Fuel filter the inlet drops to 8mm - so some restriction here a 10mm pre filter would seem better but then its outlet is 8mm as is the inlet of the fuel pump

4) The OM Lucas PRV filter had some small particle debris (see Pic) but given the work involved to get to it and the above I replaced with a modern PVR set up for Bosch pump from Prestige.

On running the pump it was noticeably quieter than before even after 5 mins run time. She fired up on the second attempt today which is better than before and ran the best she has so far for around 50 miles. She seems smoother. Fingers crossed it was a sticky PRV which in fairness having being sat for 3 years awaiting fitting might not have helped the situation.

Time will tell. Just need to smooth the idle the best I can and balance the TB's.

Andy

 

  

[Waldi]

Hi Andy,
that looks promessing.
My PRV was stuck after one winter; it had been reconditioned and adjusted during rebuilt by Neil Ferguson a couple of years earlier. 
When I opened it, there were no particles (I have a large Sytec pre-filter), but I think the brass jet in which the shuttle moves was slightly corroded by the fuel in the winter months; since then, I use Stabil in the winter per Mike’s (“Mike C”) recommendations and the issue did not re-occur.

Waldi