Djet running way too rich... Still! Options

[Halfnelson]

Had a previous thread starting in 2022 about my 73 1.7 standard D-Jet running way too rich and flooding to the point where it wouldn't start. It's been an ongoing issue. I've had a go. 2 garages have had a go. I'm at the point where I'm beginning to lose hope.

A recap. Bought the car 2021, had a problem with intermittent flooding. So far have:
Checked MPS - holding vacuum.
Replaced CHT sensor and tested. Working when flooded.
Replaced fuel pump and tested pressure.
Replaced all vacuum hoses and tested for leaks.
Valves set and rechecked.
New 123 distributor.
New injectors.

Each time I think I've cracked it and it runs and drives - sometimes for a month or so. Then I'll go to start it and it'll flood again to the point where it contaminates the oil. I feel like I've never managed to get to the bottom of the problem. Just keep replacing parts. Thinking maybe a return line that intermittently blocks? I'm kind of at a loss.

[Dave_Darling]

I had an ECU that would open the injectors, but not close them. It was an intermittent problem at first, but then became more frequent as time went on. Apparently an output transistor failing can cause this.

I hydro-locked the engine trying to start it at one point.

--DD

[Halfnelson]

I had an ECU that would open the injectors, but not close them. It was an intermittent problem at first, but then became more frequent as time went on. Apparently an output transistor failing can cause this.

I hydro-locked the engine trying to start it at one point.

--DD

Thanks for the feedback, think I’ll try to source good replacements for ECU and MPS and go from there. If it’s the MPS it would be frustrating as it hold vacuum so that was one of the first things I’d taken off the list of potential culprits, but the feedback suggests they can still be bad so I was almost certainly too optimistic.

[rjames]

I had an ECU that would open the injectors, but not close them. It was an intermittent problem at first, but then became more frequent as time went on. Apparently an output transistor failing can cause this.

I hydro-locked the engine trying to start it at one point.

--DD

Thanks for the feedback, think I’ll try to source good replacements for ECU and MPS and go from there. If it’s the MPS it would be frustrating as it hold vacuum so that was one of the first things I’d taken off the list of potential culprits, but the feedback suggests they can still be bad so I was almost certainly too optimistic.

Another reason why you might want to change the ECU first and independently of the MPS:
MPSs often need to be tuned to match the engine they are mated to. Any replacement MPS you get could run rich or lean before being tuned for your engine.

I'm sure the experts like Jeff B. have seen it more often, but I can only remember one specific instance reported on this site where an MPS that held vacuum seemingly didn't operate correctly.

[JeffBowlsby]

...but I can only remember one specific instance reported on this site where an MPS that held vacuum seemingly didn't operate correctly.

I don't consider myself an expert but holding vacuum is only one of several conditions that can cause MPS failure. I have seen several erratic MPS behaviors, which may be vacuum related or not, all can be repaired if the fault can be isolated. BTW, for anyone trying this, using ones mouth to perform the vacuum test is completely ineffective. Use a real vacuum pump with a gauge.

Other considerations:

Fractured diaphragm
Case/gasket/MPS plug/check valve leaks.
Faulty coil electrically, or coils hanging up
Distorted coil sheet springs
Bad aneroid cell

There may be additional issues not listed that effect the MPS function. These conditions may need attention or parts replacement when rebuilding an MPS, its typically not just a simple diaphragm and gasket replacement. Not all gaskets are in the kit, not all vacuum leaks are easy to locate. Often the MPS is opened-closed-reopened several times before it all works like it should.

Also consider the time it takes just to open the case initially, remove the epoxy, tap all threaded holes, perform the calibration (which can take an hour or two sometimes even if you know what you are doing, especially if someone has messed with the original calibration before), and clean/paint the outer case when necessary.

[Halfnelson]

...but I can only remember one specific instance reported on this site where an MPS that held vacuum seemingly didn't operate correctly.

I don't consider myself an expert but holding vacuum is only one of several conditions that can cause MPS failure. I have seen several erratic MPS behaviors, which may be vacuum related or not, all can be repaired if the fault can be isolated. BTW, for anyone trying this, using ones mouth to perform the vacuum test is completely ineffective. Use a real vacuum pump with a gauge.

Other considerations:

Fractured diaphragm
Case/gasket/MPS plug/check valve leaks.
Faulty coil electrically, or coils hanging up
Distorted coil sheet springs
Bad aneroid cell

There may be additional issues not listed that effect the MPS function. These conditions may need attention or parts replacement when rebuilding an MPS, its typically not just a simple diaphragm and gasket replacement. Not all gaskets are in the kit, not all vacuum leaks are easy to locate. Often the MPS is opened-closed-reopened several times before it all works like it should.

Also consider the time it takes just to open the case initially, remove the epoxy, tap all threaded holes, perform the calibration (which can take an hour or two sometimes even if you know what you are doing, especially if someone has messed with the original calibration before), and clean/paint the outer case when necessary.

hi @JeffBowlsby - while I'm sourcing an ECU can I ask, if it does turn out to be the MPS is it possible to simply replace the MPS with a known good second hand MPS? I get the notion of rebuilding the original and then having to calibrate it, but would a fully functioning MPS not just plug in and improve things? Thanks