Warm start issue

[bytes311]

I have a strange warm/hot start issue that I can't seem to figure out.

If I shut the car off after the engine warms up and then try to immediately restart it, it cranks and cranks as though it's not getting enough fuel. I can hear (and feel) the pump prime. If I perform the plug swap, the engine starts right up. But then as soon as I shut off the engine and try to restart it again, same situation.

I pulled out my dwell meter and the A/F ratio is within spec. The FV buzzes just fine. The accumulator is two years old, but it IS the later, smaller-styled one. No kinks in the lines from what I can tell.

Do our gas tanks pressurize? Because the gas cap that I have doesn't lock or tighten. I ask because I'm wondering if the problem is with the (Hervey) fuel pump. Maybe it's not creating enough pressure to suck fuel through the lines? I don't know.. I'm kinda grasping and straws now.

Thanks!

[David T]

If you do the "plug swap" and it gets you started, hot, you have a rest pressure problem. It could be the check valve by the fuel pump, the "O" rings in the PPR, or the accumulator. The small one should be OK but if you have a leaky check valve or PPR it cannot hold the rest pressure up long enough.

[NckT]

You'll need to do a fuel pressure test.
This will indicate if when you turn the engine off, what the test pressure is.

If the fuel pressure is lost quick then you've got a problem with the fueling as it should retain rest pressure of half shut off pressure after 10 minutes.

Assuming that the "new smaller" accumulator is sized to oem capacitance, then the usual suspect is the O rings on the fuel distributor primary pressure regulator, or the check valve (one way non return valve) from the outlet of the fuel pump has failed, causing the accumulator to dump pressure back in to the petrol tank.

It's not scientific, but if the accumulator goes "boing boing boing" as the spring presses the diaphragm releasing the fuel slowly then there is the greater chance it's the O ring not the check valve. This isn't always accurate though !

It's cheaper and easier to change the O rings than the check valve.

The above assumes that the new accumulator is working fine and fit for purpose, as I would always stick to oem specification.

I hope it's an easy fix for you.

Nick

[bytes311]

Hmm okay, so it could possibly be related to leaky fuel pressure? Even if I shut the engine and attempt to start it within a few seconds?

I initially suspected it to be fuel pressure, but wasn't positive because there was a good amount of resistance on the air flow meter. I tried pressing down on the metering plate a few times to get it to "prime", but the engine still wouldn't kick over.

[Bitsyncmaster]

No start after a few seconds of shut down would not be caused by rest pressure loss. But the fact you got it started using the plug swap does indicate you are not getting fuel via the FD. I agree you need to start testing fuel pressure. I would also suggest you test that fuel pressure on the hot engine. Verify primary pressure around 75 psi and control pressure around 50 psi on that hot engine.

[bytes311]

Thank you all for your suggestions.

[Jonathan]

Would a sticky plunger in the FD cause this?

If the air plate is on the other end of the lever arm that goes up and down in unison with the FD plunger, then maybe what is happening is it gets stuck in position when the engine is turned off? Then it only gets going again once the plug swap sends fuel into the engine via the cold start valve and unsticks itself because of the air pulling in?

Is any of that even possible?

[bytes311]

Just want to follow up on this issue.

I pulled out all the injectors and jumpered the RPM relay to perform the spray pattern test. Two injectors (one on each side) didn't crack open. I swapped one of the bad ones with a known good one and it sprayed. I'm going to get them cleaned up and that'll hopefully resolve my issue. I'm not sure how long they've been this way, because I've never had any issues with idle, or full-throttle responsiveness.

[bytes311]

Looks like I need a new set of injectors. I tried blowing them out with a can of seafoam and a compressor, which did appear to work because the fluid atomized out of the nozzle, but the pressure may have been too strong because now the injectors wont crack open with the RPM relay jumped and the throttle plate pushed down. <sigh>

[David T]

The injectors can't be cleaned that way. You need to send them out to a Delorean vendor or find a Volvo dealer that has the tester/cleaner. Try to have them cleaned, it is a lot cheaper than replacing all of them.

[bytes311]

Hi David: I did just that this morning after reading your response. :) I located a shop in town that work on Volvo engines and can clean/test injectors.

[bytes311]

Got my injectors back. The shop said they back-flushed the injectors and all of them had a good atomized spray pattern. I put them them back on my car and jumpered the RPM relay to witness the spray pattern for myself but none of the injectors cracked open with the plate depressed. The car starts and runs just fine though. Weird. :8ball: I restarted the car several times while warm and it fired up every time. Fingers crossed dirty injectors was the issue.

[bytes311]

Sorry to bring this topic back up. I'm still trying to figure out if I have issues with my fuel injectors.

After sending the injectors off to have them cleaned and then put back on my car, my engine runs and sounds great. No loss of power. No misfire. But when I tried to perform the injector spray test again with the RPM relay jumped, only three injectors cracked at the same time. Two injectors seem to switch off between each other, for example: depending how hard I press on the air plate, one injector sprays while the other is dry, and vice-versa. It's as if there's not enough fuel pressure in the system to crack open all six injectors at once. I have Hervey's aftermarket fuel pump, and I don't know what the PSI rating is. There are no fuel leaks as far as I can tell, and I just changed the PPR o-ring last week which cured my hot start problem. With all of the injectors taken off the lines, I get the same amount of fuel at each line.

[David T]

If they cleaned and tested the injectors correctly with the right cleaner/tester,they should have tested the opening (cracking) pressure. You can never get them all to work exactly the same but they can be close. I doubt that is the problem. Exactly what is the symptom you are experiencing when you say you have a warm start problem? If you have the classic hot restart problem and the plug swap gets you going, you are going to have to figure out why you are not holding rest pressure. You could get a fuel gauge to confirm but we already know you aren't holding rest pressure long enough. It is going to be (in order of probability)

Accumulator
Fuel pump check valve (especially if you have the newer style DMCH pump)
PPR
Leaks

If you don't hold rest pressure long enough for the motor to cool to the point the Cold Start Valve operates you experience the hard hot restart and by doing the plug swap you force the cold start valve to operate, getting you started. Holding rest pressure while hot prevents the fuel from vaporizing in the lines and gets the injectors to open a lot faster.

[bytes311]

Hi David,

My warm start issues went away after cleaning the injectors and replacing the PPR o-rings.

I'm just confused why only three injectors open when I do the spray test, but then my engine runs and sounds perfect, with no telltale signs that some cylinders are not getting fuel. Is fuel pressure higher with the engine running vs when the pump and relay is jumpered?

[Bitsyncmaster]

Hi David,

My warm start issues went away after cleaning the injectors and replacing the PPR o-rings.

I'm just confused why only three injectors open when I do the spray test, but then my engine runs and sounds perfect, with no telltale signs that some cylinders are not getting fuel. Is fuel pressure higher with the engine running vs when the pump and relay is jumpered?

I've seen those problems if I pressed the air plate to far. I don't think the air plate ever goes to the bottom of it's movement during normal engine running. I usually just press the air plate about half way down when testing injectors.

[Miles]

You should be able to test the accumulator by switching the ignition on until you hear the pump prime the system, then see if it's easy to push the sensor plate down.

[Ron]

My warm start issues went away after cleaning the injectors and replacing the PPR o-rings.

I'm just confused why only three injectors open when I do the spray test, but then my engine runs and sounds perfect, with no telltale signs that some cylinders are not getting fuel. Is fuel pressure higher with the engine running vs when the pump and relay is jumpered?Like David said, the injectors don't open at exactly the same time. Also, when they first open, they are not delivering at the same rate as when it's idling -- At idle, the rate is slightly higher, at which point they will be even enough...

Nope, the PPR holds the same pressure running or not.

Sounds like she's good to go to me...

[bytes311]

Like David said, the injectors don't open at exactly the same time. Also, when they first open, they are not delivering at the same rate as when it's idling -- At idle, the rate is slightly higher, at which point they will be even enough...

Sounds like she's good to go to me...

That's good to hear!

[David T]

If you feel the injectors are still not good you can try using a can of Techron to clean them up some more. If you have fixed your hard hot restart and you can get into closed loop and adjust the dwell right you are "good to go".