cis doesnt hold system pressure after pumps are off

[gorskined]

My car is finally starting to run really well thanks to the wealth of knowledge from this group i can finally see light at the end of the tunnel.
i still have a few bugs to sort. The car starts and runs great cold runs even better when hot, but after after running and then sitting for 10 minutes it wont start. I can crank away and wont fire over until the next day or i can turn the key on then pull the pump safety switch plug out to start the pumps. Then depress the sensor plate by hand. oddly i have to press it half way down before I even hear the high pitched squealing coming from the injectors as they start to spray . After the initial push, the sensor plate reacts normally. it starts rough then a few quick throttle revs it clears right up.
i have temporary in line pressure gauges on the control and the system pressure sides, so i can monitor things until i get everything sorted. When this happens before i manually depress the sensor plate the control pressure 2.8 and the system pressure 6.7 both where they should be.

as for the loss of system pressure i am not using the cis test gauge for my reading had a issue with that. Like an idiot i lowered the car lift onto it. i am monitoring the pressures by using the temporary inline gauges for the system and control pressures . both gauges loose pressure quickly once the pumps are off 6 bar to 3 instantly then 3 to 0 in about a minute. there are no visible leaks or smell of fuel but I'm not convicted even thou the injectors are new there may be one dripping.

simple recap fully rebuilt 76 930 row with new mahle p&c a long neck ic . new injectors new cold start injector new hard fuel lines new fuel accumulator new filters new fuel tank new twin o44 pumps both with new check valves rebuilt fd and fully adjustable wur. all new an6 flexible lines afr # are all good except for boost that's in the low 10s I'm working on that but should have nothing to do with this issue at hand.

Thanks in advance
Regards Ned

[flightlead404]

https://www.pelicanparts.com/More_Info/91111019734.htm?pn=911-110-197-34-M253&bc=c&SVSVSI=0588

[Alan L]

He says it has a new accumulator. I guess you can test them - I think a few threads on that.
Both pumps have check valves, so you would be expecting the pressure bleed elsewhere. It could be an injector. One way to check would be to pull them, then refit to the lines, pressurise via airplate til they spray, then shut everything off and collect in small jars what comes out - if any. It won't take a whole lot to drop the pressure.
Something does sound wrong in terms of the airplate movement before they squirt. Should happen as soon as the plate opens -1/8" sort of thing. That is determined by your idle mix screw.
Normally set (from zero baseline) by pumps running, no fuel to injectors, then turn clockwise til injectors crack open, and back off half a tunr. That should be close. May pay to check that.
Alan

[gorskined]

Originally Posted by Alan L

He says it has a new accumulator. I guess you can test them - I think a few threads on that.
Both pumps have check valves, so you would be expecting the pressure bleed elsewhere. It could be an injector. One way to check would be to pull them, then refit to the lines, pressurise via airplate til they spray, then shut everything off and collect in small jars what comes out - if any. It won't take a whole lot to drop the pressure.
Something does sound wrong in terms of the airplate movement before they squirt. Should happen as soon as the plate opens -1/8" sort of thing. That is determined by your idle mix screw.
Normally set (from zero baseline) by pumps running, no fuel to injectors, then turn clockwise til injectors crack open, and back off half a tunr. That should be close. May pay to check that.
Alan

Alan
my idle mixture screw i believe is spot on i set it up exactly how you said at warm idle. i'm running a high 13s low 14s if i move it ever so slightly in either direction the afr will lean or richen very quickly to 12 or 15 depending on what direction i turn it. So I'm pretty sure i am where i should be.

yesterday i started the car cold when i got home from work . started within a second half a crank it fired right up no hesitation a crisp smooth responsive idle like it should be. as it warmed up i watched the fuel pressures and the afr# all perfect. once everything settled out. i then drove it around put a few miles on it to check my boost afr# that i am slowly adjusting to try and hit mid 11s. I got home shut it off . pressures dropped off within a minute.
I then waited about 15 minutes went to restart took like 5 seconds of cranking when it started it sounded like it was running on 5 cylinders .

its got to be a leaking injector washing down a cylinder .
going to do the injector leak test this weekend as you described.

Thanks for your help
Regards Ned

[TurboKraft]

We had a car maybe 2 years ago that would lose fuel pressure, made re-starting it near impossible.
Brand new Euro injectors, flow tested prior to installation. Not the problem.
Tested the accumulator -- suspect, not perfect, so replaced it.
Tested both fuel pump check valves -- good.

If we pushed down on the CO adjustment plunger momentarily and engage the AFM, we could then crank and start the car.

What was left?
The pressure valve of the fuel distributor.

While we'd had the fuel distributor professionally remanufactured by the good folks in AL, it turns out they do not replace all the o-rings, specifically the ones on the pressure valve.

Valve location:


Bad o-ring: (photo source credited in photo)


Repair Kit:
#928 110 920 01 = Fuel Distributor Primary Circuit (Pressure Regulator) Kit
Cross Ref: Bosch F-026-T03-010

[gorskined]

Originally Posted by TurboKraft

We had a car maybe 2 years ago that would lose fuel pressure, made re-starting it near impossible.
Brand new Euro injectors, flow tested prior to installation. Not the problem.
Tested the accumulator -- suspect, not perfect, so replaced it.
Tested both fuel pump check valves -- good.

If we pushed down on the CO adjustment plunger momentarily and engage the AFM, we could then crank and start the car.

What was left?
The pressure valve of the fuel distributor.

While we'd had the fuel distributor professionally remanufactured by the good folks in AL, it turns out they do not replace all the o-rings, specifically the ones on the pressure valve.

Valve location:


Bad o-ring: (photo source credited in photo)


Repair Kit:
#928 110 920 01 = Fuel Distributor Primary Circuit (Pressure Regulator) Kit
Cross Ref: Bosch F-026-T03-010

They just did mine also really nice guys costly but nice people . i also had them test two sets of new injectors, 2 of them didn't have a optimal spray patters at full flow so i didn't install them .. I'm going to do a drip test this weekend . The more i thought about it i do believe its an injector issue until i read your response.

when i do restart it after sitting and still warm with good system and control it runs awful. like a washed out cylinder . some times it clears with a few revs and other times its bad enough where i don't feel comfortable keeping it running.
Frustrated i shut it down and call it a day. The next morning it always runs perfect.

. Now after reading your post and that issue with having to depress the sensor plate pretty far to hear the injector squeal . now make me think it may be that ..
Then you had this problem with the O-ring by passing i assume you had good control and system pressures running as well as when trying to restart when warm?

Thanks appreciate your response.

[TurboKraft]

Originally Posted by gorskined

Then you had this problem with the O-ring by passing i assume you had good control and system pressures running as well as when trying to restart when warm?

Yes, everything else was in spec and working great.
Cold starts were never a problem.

Concerning the injectors, it is really important to not only flow test them for volume, but also
* check the spray pattern -- is it a good even gas cloud?
* check the opening pressure is within specification
* check the closing pressure is within specification -- otherwise the dreaded "dieseling" i.e. run-on at engine shut off

And everyone seems to ignore the cold start valve. It's an electronic injector, so very easy to get tested and cleaned.

[gorskined]

Originally Posted by TurboKraft

Yes, everything else was in spec and working great.
Cold starts were never a problem.

Concerning the injectors, it is really important to not only flow test them for volume, but also
* check the spray pattern -- is it a good even gas cloud?
* check the opening pressure is within specification
* check the closing pressure is within specification -- otherwise the dreaded "dieseling" i.e. run-on at engine shut off

And everyone seems to ignore the cold start valve. It's an electronic injector, so very easy to get tested and cleaned.

that's right i never even thought of the cold start. i just assumed since its unplugged its not spraying need to check that also .. btw that's new also.
i don't know what i would i do with all my free time if it wasn't for this car..

please tell me i can simply back out the fuel regulator piston shaft thing to check the o-ring. obviously use care and caution to remove the plunger

Thanks again

Ned

[Alan L]

Yeah it comes out easy.
Just be careful things don't go flying across the engine bay as you ease it out - springs and shims. The O ring is easy to spot and change.
Good thought by Chris.
Not sure if it is the allen head screw or the hex you undo. Try the hex first.
Alan

[Alan L]

The CSV is a pig to get at in the car. But an alternative way to check it would be to blank the supply to the valve. LH 12mm hex banjo bolt on the FD. The hose that ducks under the air plate housing feeds the CSV. Find a short bolt same dia and thread and screw it in to that spot on the FD and seal on a crush washer to the FD head.
If you have to cut a bolt short, wash the threads and bolt after to remove any filings - you don't want them in the FD. You could just bolt the banjo fitting to the head this way - but some fuel may escape past the bolt threads. better to get a shorter bolt and seal against the FD without the banjo union.
Another good call by Chris.
Alan

[gorskined]

Originally Posted by Alan L

The CSV is a pig to get at in the car. But an alternative way to check it would be to blank the supply to the valve. LH 12mm hex banjo bolt on the FD. The hose that ducks under the air plate housing feeds the CSV. Find a short bolt same dia and thread and screw it in to that spot on the FD and seal on a crush washer to the FD head.
If you have to cut a bolt short, wash the threads and bolt after to remove any filings - you don't want them in the FD. You could just bolt the banjo fitting to the head this way - but some fuel may escape past the bolt threads. better to get a shorter bolt and seal against the FD without the banjo union.
Another good call by Chris.
Alan

great tip
i was thinking about what would be my plan of attack, during my staring at the motor last night thinking wtf. The quality of stuff today really suck . then i got nauseous thinking about how many new internal parts i have in the motor.

Then i realized everything before and after the fd is an6 i can temporarily install an inline valve just before the fd to quickly rule out everything before the fd. Then i was going to do the injector test then csv (like you said impossible to access) then O-ring because i don't want to screw with that unless i am 100percent sure its not anything else.
Now given your tip I'm going to to the csv test before the injectors. my money is on injectors or csv given the running so awful when i do get it started after a shut down .

Thanks a bunch

[SG930]

Sorry this is off topic but what product are you using to read your afr's? I had a similar issue as you but it was the fuel accumulator keeping me from restarting warm/hot. Good advice here! Thank you.

[Alan L]

You need an M8x1 (fine thread) bolt. Preferably no longer than approx 10mm/ 1/2".
Make sure the threads are right up the shank. If not quite - you will need to space with a few crush washers. I would skip the banjo bit and block it completely with a regular bolt. That way you are sure nothing is getting to the CSV.
Alan

[gorskined]

Originally Posted by SG930

Sorry this is off topic but what product are you using to read your afr's? I had a similar issue as you but it was the fuel accumulator keeping me from restarting warm/hot. Good advice here! Thank you.

Using a AEM 30-4110 Uego wideband controller the gauge is mounted in my center console.
The wide band senor it came with is garbage all the cheap eBay Bosch one are counterfeit ,readings were all over the place eventually I bought a Bosch lsu49 from Napa works great now.

[gorskined]

Originally Posted by Alan L

You need an M8x1 (fine thread) bolt. Preferably no longer than approx 10mm/ 1/2".
Make sure the threads are right up the shank. If not quite - you will need to space with a few crush washers. I would skip the banjo bit and block it completely with a regular bolt. That way you are sure nothing is getting to the CSV.
Alan

I actual had the correct wide shoulder plug with crush washer for it.. I can rule out the csv pressure still dropped like a stone when I plugged it.

[gorskined]

[gorskined]

[gorskined]

should there be air bubbles in the return line. I would think no but thought I should ask . ... I removed the return banjo and installed a banjo on a long clear hose to see if free flowing a return into the tank
via the fill would make a difference with the pressure bleed off .. it did not ... But when in did that I noticed a ton of air in the line, that never stopped . So where is it picking up the air?

[Alan L]

The fuel may be de-gassing with the pressure drop after exiting the FD.
I guess the next check will be the Sys pressure regulator - O ring that Chris mentioned. 5 min job.
Unscrew the hex on the side of the FD where Chris indicated. Slowly pull it out. If there was residual pressure in there it may fly out.
Alan

[gorskined]

I called flow tech to ask them about the air in the fuel .I couldn't get a straight answer. I usually speak with Dale but he had the day off. The guy I did talk with said if the oring is bad it's due to the ethanol in the fuel. And these cars should not be run with ethanol fuel. I live in CT and ethenol had been in the fuel since the 70s. I put 200k miles on my 74 911 with the original fd no issues. I find that hard to believe the oring would go bad in less than 20 miles. I do understand ethenol does lessen oring life but 20 miles?. So when I had time today I did remove
The oring it was not smooth it had uniform ridges on it see next post . I'm going to call back on