Djet Mixture Issues, Runs lean then rich Options

[dlee6204]

I'm attempting to get my car running correctly but am seeing some odd results in the AFR. Im seeing two extremes in the AFR during the warmup process.

Backstory: I acquired a 73 2.0L that I've known for some time. The previous owner converted to carbs because the original FI wouldn't run quite right when warm. The car ran great with carbs. I refreshed the motor, rebuilding the top end, and made it a 2056. At the same time I installed the original FI to get it working again which is the stage I'm at now. I'd like to see consistent results before I start tuning the MPS for the larger displacement.

During the first 6 minutes of start up/driving the cars runs way lean. Idle mixture is 16+. Cruise afr is 15+. WOT starts at 11.5 and ends at 13.5ish.

After 6-7 minutes of running it's like a switch is flipped. Afr reading across the board is less than 10.5. I can get it to idle around 12 but that is with the ECU knob at full lean

Some more notes....

-CHT is new. Measures approx 2200ish at 70 degrees. Once warm it is approximately 50 ohms.
- Intake temp sensor measure 180ish at 75 degrees.
-Wiring harness is a brand new refurbished harness from Bowlsby
-Mps holds vacuum. I even opened it up and checked the diaphragm. No cracks. I also checked the resistance of the coils and it checked ok.
-ECU matches the MPS
-Injectors were sent out to be tested cleaned.
- I've driven maybe 20 miles on this setup since refreshing the motor.
-I see the mixture change after 6-7 minutes whether it's idling or I'm driving
-I can plug the AAR and I still see the same results.
-I adjusted the TPS with no change.

Anyone have any additional advice or theories as to what's going on?

[76-914]

Does the new CHT sender match. IIRC, '73 used a different CHT. Maybe a one year thing. Not much help. Been away from DJet for awhile. (IMG:style_emoticons/default/beerchug.gif)

[worn]

I had the idea that there were problems with the ecu for that year with the early 2 .0s. The problem was that the ecu was originally designed for the 1.7s. But I also thought they were lean at cold start. You might look into trying another cht.

[TheCabinetmaker]

The 73 2.0L ecu needs a ballast resistor from the cht for warm-up resistance.

[dlee6204]

Does the new CHT sender match. IIRC, '73 used a different CHT. Maybe a one year thing. Not much help. Been away from DJet for awhile. (IMG:style_emoticons/default/beerchug.gif)

The CHT I’m using is 012 which is not the correct one for ‘73 however the 012 has a higher cold resistence which should make the mixture richer. The exact opposite from I’m seeing. This cht was sourced from 914rubber but I do have a Bosch replacement I could try if all else fails.

[JeffBowlsby]

Faulty CSV maybe? If its intermittently leaking, that may explain the richness. Take it out of the fuel loop by clamping the fuel line and see what happens.

[mgphoto]

I would check the vacuum, cam could be the issue.
FI cam and carbs don't match as carb cam and FI also doesn't.
Also this will rule out mechanical issues.

[dlee6204]

Faulty CSV maybe? If its intermittently leaking, that may explain the richness. Take it out of the fuel loop by clamping the fuel line and see what happens.

The line to the CSV has been removed and I have a pressure gage currently there.

[dlee6204]

I would check the vacuum, cam could be the issue.
FI cam and carbs don't match as carb cam and FI also doesn't.
Also this will rule out mechanical issues.

Cam is the stock cam. The cam was never changed for the carb swap.

[dlee6204]

Possible progress!


On my lunch break today I rechecked a few things and then went on the hunt to see if I had a spare 037 ECU. Turns out I did! I swapped the ECUs, started it up, and let it warm up. While cold, the idle mixture was hovering around 16 and after about 10 minutes it only dropped to 14 and that’s where is stayed so it didn’t go full rich this time. I didn’t go for a test drive but will do that when I get home tonight. Hopefully I now have a reliable baseline so I can start tuning.