Mystery D-Jet lean condition., mystery no longer... Options

[Olympic 914]

Car started going to an intermittent lean condition.

'73 2.0 d-jet system 037 ECU.

Starts up fine, idles Ok.

But when I start to drive it, it starts running bad and the AFR goes to 17-18, Sometimes if I feather the throttle I can keep it running and it settles back to 12.5 – 13.0, normal running.

Other times it dies. It will start right up again though.

I have a fuel pressure gauge but it is mounted in the engine compartment and I can’t see it when driving. Pressure is set at 29 now. and holds at that during idle

In January I had an issue with the fuel pump wiring, So I redid the wiring with 12ga from the rear to the front. I didn’t like the sound of the Bosch 044 pump, it was way too loud.

So I installed a Bosch 69133 pump. Much quieter, drove it around for a while and everything was working perfectly.

Spent all of February doing a cut and buff on the car, then drove it for a bit again everything still working fine.

The most recent thing I did was remove the rear brakes to fix my parking brake. Didn’t touch anything in the engine compartment. But when I took it for a drive after working on the brakes the lean condition arose.

I had already purchased a FI harness from Bowlsby So I took the opportunity to install it. Hoping that would solve the problem.

Well it didn’t.

Have a ¼ tank of gas, and I checked it with a dowel rod to make sure the gauge wasn’t reading off. Then added 2 gallons anyways.

Still no change. Changed out the fuel pump relay, No improvement.

I have no idea what brought this problem on. I can’t rule out the new fuel pump. But it ran good with it for at least 200 miles. Changed the fuel filter and cleaned the screen when I had the tank out. the screen wasn't dirty though. The tank was cleaned before I put it back in 4 years ago. No rust inside.

At this point I won’t go further than around the block, and it will happen a couple times on each trip around. But hasn’t stuck me totally yet.



Guess I could set up the endoscope to watch what the fuel pressure reads when it goes lean and take it from there.

I have to just walk away from it for a while, but my mind is reeling.

[DRPHIL914]

dont rule out a bad MPS just due to lean condition. the fact that it is up and down makes me think MPS, i have had this very thing happen. it was a failing MPS. when i was driving this last fall i started to see this fluctiation of sudden change in my AF reading, suddenly lean then back to normal, in this case it was my TPS with corroded contacts, it was also bucking at times, if you are seeing this check the TPS board, clean it with an eraser and see what happens, but to test it just unplug it, i did this and immediately the bucking was gone. - test the TPS , if not that go to the MPS and thne also the CHT could have a bad connection and do this as well,

Phil