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.

You are doing the right thing to monitor your fuel pressure, it could be the key.


With the new harness that removes electrical related issues assuming all connections are well seated.

Clogged or defective injector(s) restricting fuel delivery?
Bad trigger points skipping a few pulses now and then?
Bad ECU?
Bad MPS?
Bad TPS?

i don't have a d jet, but a 1.8 L jet.
but experienced similar sounding problems.

homing in on delivery to the fuel pump having worked through everything else.
or it could be the fuel pump itself.
which is new.
not sure.
its a bosch pump.
every now and then it sounds crazy and is making a lot of noise.
then quiet again.
so either its not getting fuel or its having problems itself.
i got a lot of good tips/advice from guys here to help me zero in on it.

I think Jeff is on the right track. TPS, MPS are easy enough to check. Pull the dizzy & clean up the contacts. Just do them all one at a time so if the car runs better you know which item was the culprit. Also verify your ECU & MPS are both for MY 1973- I know, if mismatched it wouldn't have run well before but it's an easy thing to check. Hope you get it sorted out.

I would suggest getting a longer piece of fuel hose and routing the fuel pressure gage to the cabin so you can read fuel pressure while driving. It's simple and will rule some things out.

I'm not saying its your issue but I would add the ECU higher on the list of suspects. I've seen more of these "bad" as of recently. My last '73 I had three ECU's with the same part #, and all made the car behave differently. One would cause the car to go full lean after 2-1/2 minutes of running.

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

I have narrowed the problem down to a fuel / fuel line / fuel pump issue.

It will idle fine in the driveway for an extended period without problem.

But once I pull out of the driveway and start up the slight hill the pressure drops, Push in the clutch and it recovers. Then starting up a longer hill the pressure again drops and the car will stall. it will restart immediately. various other places when the engine is under load the pressure will drop. It does the SAME thing in the same places.

I believe that there may be a kink in the line that is only allowing a small amount of fuel to pass.

I can drive down a straightaway in first with barely any throttle on it and the pressure stays up. As soon as I accelerate the pressure drops and it begins to die.

I hooked up a scope to view the pressure gauge during these drives.

https://youtu.be/TXtff1gE7h8

First is idling in the drive, at 30 sec pulling out of the drive and the pressure drops, then at 48 sec the pressure drops again as I start up a hill about 200yds from the house continuing up the hill and at 1:08 it dies, quick restart and pressure is back up.

I will first try to access the lines through the hole below the tank, If that doesn't work I will have to remove the tank and reroute the lines.

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.

Removed the tank and confirmed that there was restriction in the line.

One spot had a kink and another spot looked sucked in on the inside of a bend.

I have some 3/8 stainless braided line left over from a motorcycle project, I am looking at installing it. That stuff won't kink. I'll use it on the feed line from the tank

Having problem finding 7/16 (11mm) hose to go over the inlet port of the Bosch 69133 fuel pump. Two Flaps claimed it was in stock and when I got there it wasn't.

Am on my way out now to a third that said he had the hose in his hand. Hope he wasn't Hosing me.

I use half inch racing hose for the 12mm section between the filter and pump.

Solved it.

The problem was the fuel lines were kinked or being sucked shut.

Took it for a drive, and it ran beautifully. Fuel pressure steady.

Installed the stainless braided hose on the feed / suction side of the pump and shortened the run of line.

This meant attaching the lines through the hole below the tank. Major PITA.

Trying to get a wrench in there I could only get 1 - 12th of a turn on the hose clamp. took forever to tighten them up. Maybe a job for someone with smaller hands.

Glad I won't have to do that again for a while.

Bonus.. I got the new FI harness installed. Even though it wasn't the problem.

Nice job, Tom!

great.
be thankful you can still get to the hoses through the access port.
mines rhd and the port unfortunately is more or less gone.

enjoy driving.