Fuching DJet issues *SOLVED*, Running out of things to try Options

[rjames]

Last summer all of a sudden my car wouldn’t stay running. If I could get it started the idle would hunt and the car would die unless I kept on the gas. Lack of power at times. All somewhat erratic.
Found that the MPS wouldn’t hold vacuum.

Replaced the bad mps with a known good one. Car idles high when cold (higher than I think it should ~1600 rpm) so AAR is good, then when it warms up idle hunts from ~900rpm to the point where it almost dies unless I open the throttle body bleed screw quite a bit and turn the ECU knob just a few clicks away from full clockwise.

So I did the following hoping to fix the issue:
Replaced all vac hoses including intake runner to plenum hoses.
New intakecrunner gaskets
Verified plenum isn’t leaking
New throttle body gasket
Installed NOS throttle body
Rebuilt the distributor
New condenser
Rebuilt injectors and flow tested
New fuel lines
Fuel pump is less than 2 years old
Set timing and dwell with advance disconnected
New CHT (resistance reads 1.7 w/engine off @70 degrees in the garage)
Calibrated the TPS, even unplugged it to take it out of the equation, didn’t change anything.
ECU matches the MPS (both correct part #s for a ‘75 2.0)
Tried a known good ECU from a ‘74, no change.

Feels like the MPS needs to be calibrated...but then again, these are all the same symptoms I had with the old bad mps. Replacement mps is from a Jeff B and was tested, but I haven’t retested it to see if it’s holding vacuum.
(Don’t have the necessary tool, but maybe that’s the next step)

Help! What am I missing?

[GregAmy]

Just a note on "known good MPS"...I was having terrible driveability problems with my '74 2L, similar to yours, and tried pretty much everything. Tested the MPS and it held a vacuum. I was stumped.

I was lamenting my probs when the guys at Tangerine said, "rebuild the MPS". "It's holding a vacuum" I replied. "Rebuild the MPS". So I gave them the MPS to rebuild.

It transformed the car. Car drives great now.

Turns out the diaphragm was cracked (Chris showed it to me) but somehow it was holding a vacuum anyway. Oh well.

[BeatNavy]

Based on hunting idle it sounds like you're running too lean. That would be first suspect, but you should try to identify the broad root cause and then narrow down from there. What can you do to test if it's fuel delivery (too lean or too rich) and not something else like ignition, charging system, or vacuum? I assume you don't have a wideband O2 sensor. Have you tried unplugging the T1 (ambient air) sensor to see if that has an effect?

You've done a lot, but I would also recommend:

1. Verifying fuel pressure.
2. Inspecting/cleaning PCV valve.
3. Inspecting wiring harness for cracks, shorts, cleaning grounds, etc

[Bleyseng]

I can loan RichD my wideband to check the AFR on your car. I agree with checking the wiring harness.
I also have a Janbo Djet tester I can loan RichD to test your system.

[rjames]

I just installed a wideband sensor on my car but haven’t looked at the readings yet since keeping it running at all has been a challenge and knowing that the air fuel mixture was likely way off because trying to keep it running requires openening air bleed screw on the throttle body quite a bit.
I will check the readings though.

[rjames]

Based on hunting idle it sounds like you're running too lean. That would be first suspect, but you should try to identify the broad root cause and then narrow down from there. What can you do to test if it's fuel delivery (too lean or too rich) and not something else like ignition, charging system, or vacuum? I assume you don't have a wideband O2 sensor. Have you tried unplugging the T1 (ambient air) sensor to see if that has an effect?

You've done a lot, but I would also recommend:

1. Verifying fuel pressure.
2. Inspecting/cleaning PCV valve.
3. Inspecting wiring harness for cracks, shorts, cleaning grounds, etc

No PCV on ‘75 or ‘76 year cars- the hoses are connected directly to the air filter housing.
What is the T1/ambient air sensor located?

[BeatNavy]

What is the T1/ambient air sensor located?

It's inserted into the top of the plenum and has a 2-wire connector on it. Disconnecting the connector opens the circuit, and ECU interprets that as the coldest possible ambient air temp and enrichens the mixture somewhat to compensate. Not nearly as much as CHT, but enough to normally notice a difference.

Definitely verify fuel pressure.

[IronHillRestorations]

Trigger points

[914_teener]

Post a pic of your engine compartment.

Are you running a decel valve?

So your d jet setup is for a 74 2.0?

[rjames]

I'm using the decal valve.
75 2.0 with smog removed.
Using '75 ECU, MPS and appropriate CHT sensor.

I just rebuilt the distributor and installed new trigger points- didn't change anything.
Fuel pump is new, but that doesn't mean it's working correctly or the pressure is set correctly. That said, if it runs at ~1600 rpm when cold for a few minutes, it seems unlikely there's a fuel pump/pressure related issue. no?

I'll try disconnecting the T1/ambient air sensor to see if that changes anything.
Measuring fuel pressure is on the list too now.

How do I tell if the distributer is working correctly?

It still feels MPS related to me...

[BeatNavy]

If you disconnect the T1 sensor I just want to see if things get incrementally better. If so, that might suggest a lean condition (also possibly suggested by the hunting idle). From there you could look to the actual root cause. But without a wideband sensor or other info it's hard to tell what the actual situation is (too lean, too rich, neither), and so to some extent you're chasing your tail.

Normal MPS failure is toward a rich situation. Why do you think it's MPS related? MPS's are pretty easy to test.

When you installed the new trigger points, did you calibrate them at all?

[rjames]

If you disconnect the T1 sensor I just want to see if things get incrementally better. If so, that might suggest a lean condition (also possibly suggested by the hunting idle). From there you could look to the actual root cause. But without a wideband sensor or other info it's hard to tell what the actual situation is (too lean, too rich, neither), and so to some extent you're chasing your tail.

Normal MPS failure is toward a rich situation. Why do you think it's MPS related? MPS's are pretty easy to test.

When you installed the new trigger points, did you calibrate them at all?

I have a wide band sensor. Will check readings tomorrow along with disconnecting the T1 sensor.
I suspect the MPS because this all started happening when the original MPS went bad.
Bought a replacement from Jeff Bowlsby that he tested and the same symptoms remained after install. Or maybe that’s a reason not to suspect the MPS.
How do I rule out the distributor?

[JeffBowlsby]

Its frequently the case when the MPS is going bad...that the system has been adjusted to compensate for a failing MPS. Then when the new good MPS is installed...the system itself is not in adjustment and seems wrong. Fuel pressure is changed, the air bleed screw is changed, the ECU idle mixture knob is changed and who knows what else.

For example, it was not mentioned above that the fuel pressure was checked. Its basic and important so use a gauge and check it. Then balance idle sped with the air bleed screw when warm.

Is the cold start valve leaking? Test it or take it out of the system.


Are there any vacuum leaks...gaskets, fuel injector tip seals, the air plenum etc.?

All these can affect idle and mixture.

[rjames]

Its frequently the case when the MPS is going bad...that the system has been adjusted to compensate for a failing MPS. Then when the new good MPS is installed...the system itself is not in adjustment and seems wrong. Fuel pressure is changed, the air bleed screw is changed, the ECU idle mixture knob is changed and who knows what else.

For example, it was not mentioned above that the fuel pressure was checked. Its basic and important so use a gauge and check it. Then balance idle sped with the air bleed screw when warm.

Is the cold start valve leaking? Test it or take it out of the system.


Are there any vacuum leaks...gaskets, fuel injector tip seals, the air plenum etc.?

All these can affect idle and mixture.

No vacuum leaks detected. see above for all of the items that have been replaced and/or checked already.

Cold start valve has been removed from the system to no effect.
Besides the bleed screw on the TB and the ecu knob, and fuel pressure, is there something else that could be adjusted for a failing MPS that would make the car undriveable with a good MPS? (All inection components are stock.)

Fuel pressure is on the list to check next.
Distributer is still in question.
MPS is still in question.
Wiring harness possibly, but seems unlikely.

Symptoms originally occurred when the MPS went bad. Seems unlikely that something would’ve happened to the wiring harness, distributor, or fuel pump/pressure or wiring harness at the same time.

[sixnotfour]

food for thought
http://www.914world.com/bbs2/index.php?sho...=338162&hl=

[rjames]

food for thought
http://www.914world.com/bbs2/index.php?sho...=338162&hl=

Plenum isn’t leaking.

[rjames]

Ok, more testing = more results.

Distributor canister won’t hold a vacuum. Only the retard side is hooked up, and that will effect idle, (if I understand how it works correctly), but if I disconnect the retard hose and plug it at Bothell the TB and the dizzy, issue is still there.

So after finding that issue...
With all hoses disconnected and capped my AFR tells me that ratio goes from 14 to full lean in synch with the fluctuating idle.
I don’t have a tool to measure fuel pressure (yet) but I did stick my ear down by the fuel pump and it gets louder/quieter as the idle surges up and down. Hmmm... May have just identified the main culprit.

Hopefully it’s just a clogged fuel filter, or it could be a bad pump (even though it’s a new Bosch unit(which would $uck). I cleaned the tank and installed new sock a few years ago so that should be ok.

Can I run the pump without fuel for any length of time without damaging it to test it?

So...
Where can I get a good distributor canister? Are they rebuildable?

[BeatNavy]

Good news is it sounds like you confirmed the condition (lean), and you are getting closer to the root cause (failing fuel pump or possible obstruction in the line somewhere). Fuel pressure gauge would confirm it's on that path. BTW, don't cap the ports at the canister. Those need to be able to move.

The stock pumps are somewhat cooled by fuel running through them, so running without would burn them out (at some point). Not sure about the newer Bosch units. I figured those are pretty reliable (I have been running one about a year now), but who knows?

I'm not sure about the canister. Either WTB for canister or bite the bullet and get a 1-2-3? It's pricey, but works like a champ. I'd work to get the fuel delivery situation resolved and then reassess the distributor.

[jagalyn]

Found this series of D-Jet Articles online.

https://oldtimer.tips/index.php/en/d-jetronic/51-history

[saigon71]

You are running lean at idle. Try truning the ECU knob to the full clockwise position.

I don't know if it's the ethenol in the fuel or what, but my 914 idle hunts the least with mixture knob set to full right (clockwise).

I don't think this will fix your problem, but may improve it.