Hot start issue CIS With VIDEOs

[Mtsurfposse]

1983 ROW SC

been having this issue since I bought, previous owner had it too. Ive gone basics last year and keep thinking ive found it only for it to reappear. Its usually worse in hot weather, and we have had that in spades the last two weeks.

Heres the quick run down
cold starts fine
once car has run and oil temps in middle
5-7 minute start fine
10-15 no start
no start for at least 1.5 hours
2+ usually

I'm thinking its fuel accumulator or pressure relief valve in distributor. Often I could tap air plate and hear injectors open. Sometimes, seeming more lately but only because Im making notes of this, even lifting air plate to max height, i do not hear injector squirt.

5 minute hot start
https://youtube.com/shorts/lTZmAsARKIY?si=UwiHyL9mFbxJiv5J

greater than 10 minutes:
https://youtube.com/shorts/wn11k-f8z10?si=gsoXNIzop3dyYK_R

[Mtsurfposse]

The WUR values are in spec
the residual pressure is in spec but is high. Hours later still 1.5bar
air plate is in spec
idle bypass at 1.5
AAR working, its been opened and sorted
AAV working, bench tested
Decel vavle functions as should

Car runs great once started, no issues, coughs or hiccups

I feel The fuel injectors are not opening, when starts fail, you can watch gauge which never goes high enough to open, it’s as if vapor is in effect, or the high residual pressure doesn’t allow things to move properly at the FD valve

I just found fuel accumulator (FA) new 2022, the fuel pump and filter were also done at this time. Last fall, I backflushed filter as part of my investigation, nothing,
WUR and FD were rebuilt by a well known and respected member of the forum in 2017/8

I tried to test FA, but couldnt get the return relief fitting to break loose, its a 3 port and Im a little fuzzy on 911boys testing configuration with gauges and was going to try the air plate squirt test but will need a breaker bar attached to my wrench.

Im also not sure how it could fail and still hold residual pressure, but Im sure Im missing something as im not the smartest kid in class

Fuel Distributor (FD)? I wondering if some debris is sticking in the FD, or if the bypass needs shim adjustment, I dont know if I can pull it apart and put back together without a rebuild kit, or specific methods for testing this problem

[Showdown]

Check the o-ring and shims in the fuel distributor pressure relief valve. A tiny nick in the o-ring can cause loss of fuel pressure. You also may need to add shims to keep pressure.

You don’t need a rebuild kit to fix this- it can be done in-situ (it’s tight though) and you can buy shim material and o-rinks from McMaster Carr.


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[Mtsurfposse]

Thanks, that’s good to know, is there a way to test this valve before pulling it, or is it so easy to pull and check there’s no point in testing
Can you explain how control pressure can be within spec, but the valve can be bypassed and not trigger injectors? I’ve been looking for a good explanation of this and haven’t understood how this can happen

[Mtsurfposse]

So I just opened the bottom port on the FA and at least 1/4 cup of fuel came out. Is that too much? I’m guessing yes, but I’ve only read Vague “a small amount is ok with 3 nipple accumulators”

[Showdown]

1/4 cup is too much. It should be drips if the internals are good.


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[boyt911sc]

Originally Posted by Mtsurfposse

So I just opened the bottom port on the FA and at least 1/4 cup of fuel came out. Is that too much? I’m guessing yes, but I’ve only read Vague “a small amount is ok with 3 nipple accumulators”

Place the bottom fuel line of the FA into a container to collect the fuel and another container at the bottom of the FA. And test run the FP for 2~3 seconds (max). If you get fuel coming out from the bottom of the FA during the test, the fuel accumulator is LEAKING. A good FA will show no fuel coming out during the test.


Have you checked your residual pressure? Your warm starting problem points to your residual pressure loss.

Tony

[Mtsurfposse]

Tony! Im glad you chimed in! You rebuilt the WUR and FD in this car 8 or so years ago and Ive been reading your many posts as Ive been trying to isolate this little bugger

My residual pressure is HIGH for a long time (but Bentley says >X at 10/30 minutes so I dont know if something is TOO high for TOO long.

10 minutes 1.8/1.9
30 minutes 1.6
150 minutes 1.3

Ill run the pressure test again with buckets under the line and the accumulator and see what kind of a mess I can make tomorrow

[boyt911sc]

Originally Posted by Mtsurfposse

Tony! Im glad you chimed in! You rebuilt the WUR and FD in this car 8 or so years ago and Ive been reading your many posts as Ive been trying to isolate this little bugger

My residual pressure is HIGH for a long time (but Bentley says >X at 10/30 minutes so I dont know if something is TOO high for TOO long.

10 minutes 1.8/1.9
30 minutes 1.6
150 minutes 1.3

Ill run the pressure test again with buckets under the line and the accumulator and see what kind of a mess I can make tomorrow

I have a question about your CIS pressure gauge. It looks like it has a Schrader valve. Please confirm if it has NO Schrader Valve because it will give you a false test result for residual pressure loss test.

Tony

[PeteKz]

What Tony said. Make sure the gauge is connected and working correctly.

THEN, if you are holding RP for more than 30 minutes, your FA is good. When you first crack open the fitting at the bottom of the FA, you will get some fuel out. Although it's on the return side of the fuel system, some of it will migrate up to the bottom of the FA. As Tony said, with the bottom "drain" fitting removed (and the hose plugged or placed into a container), run the fuel pump and see if you get leakage out the bottom of the FA. If so, it's bad. However, since it was installed in 2022, I doubt it's bad.

Since you have a fair amount of fuel in the bottom of the FA, I would look further downstream too, and make sure you don't have a restriction in the return lines to the tank, that might cause some of the return fuel to flow back up into the bottom of the FA.

Send a picture of your FA and filter in situ.

[Mtsurfposse]

Thanks. I’ve been away at wedding so haven’t been able to get back.

The CIS gauge is S&G tool aid company. I don’t believe it’s a schrader valve or how it be misreading excessive pressure

Is there a time tested method for checking downstream blockage? I was gonna pop off the return line at the T and blow some air through it. I’ve been thinking my EVAP SYSTEM is blocked to some degree as it seems to sometimes have helped the restarts by removing the gas cap and having a great amount of vapor audibly escape. But this could be coincidentally as it only seems to help 30% of the time.

After checking FA,I believe it’s good. Not a drop when pressurized for 3 seconds. I also would assume EVERY three port would fill with gasoline, unless there is some check valve in the T that comes from the return line to the FA it HAS to fill.

[boyt911sc]

Do you have an inductive timing light? From the two (2) videos you posted, it looks like your ignition signal is sporadic. The pressure gauge shows about 2 bar of control pressure so there is fuel in the lines.

Install an inductive light with a cold motor and repeat the test with a warm motor. This will tell you if ignition signal is a contributing factor to your problem. If good ignition signals are both present consistently during a cold and warm conditions, we could eliminate your ignition coil.

Do you have a POV? Done any smoke test recently?

Tony

[Mtsurfposse]

Smoke tested in fall and summer last year when investigating this poor/ no start. When running now, pulling oil cap drops rpm 50-100.

What’s POV?

Will hunt for induction light, I’ve been wanting to test for timing, as this cars various incarnations may have had it modded.

[PeteKz]

POV = pop-off valve. Installed in the airbox under the air filter. It allows backfire pressure to vent, to prevent busting the lower airbox.

If pulling the oil cap causes RPM to change, then don't worry about troubleshooting air leaks yet.

Check for spark as Tony recommended. Another simple test: When it is having warm start issues, squirt starting spray in the intake. If it starts immediately, you have a lack of fuel delivery problem. If it doesn't start immediately, that points back towards an ignition problem, or possibly flooding (too much fuel). DO you smell raw gasoline out the exhaust when you are having the warm start problem?

I doubt it's a failing ignition coil. Failing coils usually cause ignition missing at high RPM and full throttle, when the coil has to deliver full voltage sparks 300 times per second. Warmed up and hot and humid conditions usually make it worse. That's not what you are reporting.

[Mtsurfposse]

MAYBE SOLVED!!!
Fuel Pump relay, Checked and failed 2 ways. resistance fail and always conductivity 30-87a

installed new relay and Ive had perfect starts.
Im still holding my breath but I really think this was it. Still some chance there is a return line/ EVAP bloackage but Somehow my draining temporarily cleared things, as I am fuzzy to the circuitry and would think it would always start when in run position as the relay seemed to always have continuity from 87a to 30 but should have died when ke was turned to Run but Im sure Im missing something

that aside Im calling it a win for now, and if the problem comes back shortly I will roto-root the return line and EVAP. Right now Im going drive the bejesus out of it and enjoy the extra 25% of accelerator pedal my butt dyno is telling me I now have

This is so weird as this has been ongoing for at least 3.5 years. I cant believe it takes a relay this long to fail

[PeteKz]

If the problem comes back, use starting spray to troubleshoot as I described above.

[Mtsurfposse]

Originally Posted by PeteKz

If the problem comes back, use starting spray to troubleshoot as I described above.

Do you shove the straw past the air plate or just spray for a second into the box and quickly put the air filter back on?

[pmax]

Originally Posted by Mtsurfposse

MAYBE SOLVED!!!
Fuel Pump relay, Checked and failed 2 ways. resistance fail and always conductivity 30-87a
...
This is so weird as this has been ongoing for at least 3.5 years. I cant believe it takes a relay this long to fail

Weird if it is indeed the root cause, a FP relay which works at the 5 minute mark but not 10.

[PeteKz]

Originally Posted by Mtsurfposse

Do you shove the straw past the air plate or just spray for a second into the box and quickly put the air filter back on?

Just give it a 2-second spritz in the intake horn on the air filter cover.