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.

[wonkipop]

where is the pump located.
under engine bay location?

reason i ask, is you say you changed pump.
i did too.
i had an original 3 port - now changed to an inline.
have zeroed in on the pump plumbing and the metal fuel line (recent replacement for original plastic) section exiting firewall.
also the replumbing of flex lines into and out of pump due to space restrictions with newer in line pump are now tighter loops.
i believe i am getting boiling in the metal lines under some circumstances.
(problem did not emerge in my car until we got a burst of real aus summer weather here, its been a non existent summer until a month ago).
i also think i am getting boiling or collapse in the flex line into the pump.

i've rebuilt my original pump so i'm putting that back in to relax the curves on flex lines in and out. i'm going to wrap the steel lines in reflective insulation. i'll see if that works for what i have going on.

i checked my tank lines and concluded 90% not the problem as it was related to certain circumstances in the heat and after the engine is hot. i've got very relaxed loops under the tank and i figure if it was there it would be happening all the time, as yours sounds like its doing - related to running demands not temperatures/outside conditions.

yours sure points at a consistent problem with a fuel delivery line collapsing/constricting?
i hope it is as simple as that and not a more tricky to trace electronic issue.
nice work with the guages isolating possible problem.

the old roller cell pumps with three ports were very good on the pressure side, but fairly weak on the suction side. mostly relying on the larger diam delivery line and gravity.
i'm starting to wonder if newer pumps might be just strong enough on suction to cause lines to collapse on the delivery side that never was the case before.