A friend just picked up a late '74 2.0 with the factory DJet. We've replaced the fuel filter as it looked gnarly and are getting ready to ohm out/replace the temp sensor, but I found something strange.

The car will not start at all with the temp sensor disconnected. I thought it might run rich with it disconnected (an improvement from where we are now), but I never thought it would fail to start.

Is that to be expected? Any place to look for lean conditions across the board other than:

* CHT
* Fuel Pressure
* Idle mixture knob (all ready fully rich)

Gonna go through the entire FI/Ignition system top to bottom, but just thought I'd ask. That CHT thing is weird too...

The CHT sensor supplies a vital ground to the ECU. Gotta be there. The Cap'n

Thanks!

Air temp sensor will cause problems. Unplug it, it will run much better.

I don't recall an air temp sensor on DJet... It's been a few years though.

just to the left drivers side of the throttle body

When the CHT is open, the injection pulse durations are extremely long (>40 ms), making the mixture too rich to start.

First, what makes you believe that it's running lean? I assume this is with the car fully warmed-up? What is the idle CO? Can you measure CO while running at part-load? Just checking to make sure you're going after the right problem.....

If it really is lean, a possible reason is that someone has "adjusted" your MPS part-load to a lean mixture. Do you have a spare MPS to swap with it? Very low fuel pressure is another possibility. Idle mixture knob only affects mixture when the throttle is closed (idle and overrun conditions).

Pops and snaps like it's lean. No power. It's not billowing black smoke nor "smells" like gas. Will only idle decent with the idle mixture knob turned fully clockwise.

The *only* troubleshooting we've had time to do so far is replace the fuel filter which looked 30 years old... It's getting all new SS lines from Chris soon, but I hope to check fuel pressure before then.

I do have a good, known MPS as well as an entire DJet set up from my car which ran great with it. I'm curious about stuff like ECU and MPS mismatches too. I haven't seen a DJet car that ran like this before... First things first. Have to measure fuel pressure.

ECU and MPS mismatches won't make much difference. Nearly all setups have the same part-load mixture settings. If it's really lean, something else is wrong. Given that you said the fuel filter was grungy, it's possible that the fuel pressure regulator has been also contaminated. You also should check the injectors, if the system's been contaminated they may be clogged. Only after you've verified the fuel pressure and checked out the injector spray patterns should you move on to going into the FI components.

Agreed... I'd be surprised if the injectors were clogged as it idles smooth.

Thanks.

What is the room temp resistance of the CHT sensor? If this is low it will be lean. I had to add an extra 150 ohm resistor to mine to get it to run nicely.