Help - Djet running way too rich Options

[Halfnelson]

Help - my new to me 1973 1.7 Djet came running really sweet, but almost immediately developed the 'hunting tick-over' of lean running / air leak. We replaced all the vacuum pipes, found one of the inlet gaskets had a very slight leak. Seems somewhere along the line things have been tweaked to compensate for the leaks so that now they're cured, the car is running super rich. Having had a L-jet for years the Djet is new to me so any advice on where to start first would be much appreciated. Thanks Chris

[rfinegan]

Try adjusting the Idle mixture knob on the ECU. I think this is for setting via CO meter reading but will get you in the ball park click or two at a time and you idle will change( speed/hunting) The base line setting is bout 22 clicks or so..if I remember correctly

[jrmdir]

Welcome to the D-Jet rich mixture madness. I'm going through the same issue with my '73 1.7. Only to my limited knowledge about this car, I don't think it had a lean history that was compensated for. So far I've found a number of reasons for running rich, including disintegrated MPS diaphragm, high fuel pressure and (possibly) leaking cold start injector. Next I'm going to check the cylinder head temp sensor.

There are a number of great threads on this. Here's one that has tons of info:
https://members.rennlist.com/pbanders/DJetParts.htm (easier to search Google than here - and you most ofthen still get to 914World threads as a result.)

If your car was running lean over time and you're looking for ways that the PO might have tried to enrichen it, check out the wiring from the cylinder head temp sensor to the ECU. On our 1.7's there should be no in-line resistor, which, as I understand it was added by the factory for either the 1.8s or 2.0s - to "fool" the ECU into delivering more fuel without reprogramming the 1.7 ECU. There is some mention of 1.7 owners adding this themselves thinking it would add power (not!)

Good luck - report back if/when you get this resolved, it may be something I've yet to find in my quest.

Ron

[dr914@autoatlanta.com]

SUPER rich could be blocked fuel return, bad valve, or defective head temp sensor. REAL rich could be pad pressure sensor

Help - my new to me 1973 1.7 Djet came running really sweet, but almost immediately developed the 'hunting tick-over' of lean running / air leak. We replaced all the vacuum pipes, found one of the inlet gaskets had a very slight leak. Seems somewhere along the line things have been tweaked to compensate for the leaks so that now they're cured, the car is running super rich. Having had a L-jet for years the Djet is new to me so any advice on where to start first would be much appreciated. Thanks Chris

[ctc911ctc]

That is a beautiful car!

SUPER rich could be blocked fuel return, bad valve, or defective head temp sensor. REAL rich could be pad pressure sensor

Help - my new to me 1973 1.7 Djet came running really sweet, but almost immediately developed the 'hunting tick-over' of lean running / air leak. We replaced all the vacuum pipes, found one of the inlet gaskets had a very slight leak. Seems somewhere along the line things have been tweaked to compensate for the leaks so that now they're cured, the car is running super rich. Having had a L-jet for years the Djet is new to me so any advice on where to start first would be much appreciated. Thanks Chris

[Olympic 914]

Pull a vacuum on your MPS
Make sure your diaphragm isn't cracked

[rjames]

Pull a vacuum on your MPS
Make sure your diaphragm isn't cracked

(IMG:style_emoticons/default/agree.gif)

See if it's been opened before, too. If it holds vacuum but has been opened up (rivets replaced with screws), it may need calibrating for your engine.
Also make sure the ECU and MPS match & are correct models for your car.

[Dave_Darling]

Step 1: Check the ignition system. Yes, seriously. Make sure the timing and dwell are in spec, and that you're getting a nice fat white happy spark.

It's amazing how many "FI problems" (and "carb problems"!) are actually caused by ignition system issues.

Step 2: Check the valve adjustments. Valves that are out of whack can cause odd-seeming problems. For instance, an intake valve that doesn't close all the way can cause a very rich mixture. (Don't ask how I know that.)

Then move on to testing the parts of the FI system.

--DD

[Halfnelson]

Many thanks for all the suggestions - plenty to work our way through on Monday and I'll report back. Had a read through other similar threads - one that said CHT sensors don't often go bad - is it more likely a case of bad connections?

[jrmdir]

Hi Halfnelson: Hope this doesn't amount to hijacking your thread but since we seem to be in the same boat maybe my experience so far is of interest. (I had no knowledge in this area a month ago so take my advice with a grain of salt.) But the huge body of work on this forum has been very educational!

As advised above, I did start with valves and ignition. PO had replaced all spark related parts and I reset the dwell and timing to spec. I also installed a fuel pressure gauge and lowered it to just under 30 PSI. Next I pulled the throttle body and checked cleaned and adjusted the TPS contact tracks.

Next up, the MPS and sure enough, mine held no vacuum at all. So I replaced the perished diaphragm using TR's kit. Successfully but still in question (see below)

Next I removed and tested the Aux Air Valve - it worked but I decided to leave it off and plug the manifold outlet. Ditto with the Decel Valve. Unlike more modern FI systems with mass air flow meters, a downstream vacuum leak on d-Jet shouldn't cause a lean condition. The MPS will note the pressure drop and add more fuel. BUT, this should be in proportion to the "extra" air so it shouldn't be richer. I think:) Anyway, based on what I read it was OK to disconnect these for a while to reduce the number of variables. I may hook them up again later.

Then, to eliminate doubt re: defective Thermo switch or leaking cold start injector, I got a 3' length of fuel hose and completely bypassed the injector.

Finally, (and I should have done this earlier,) I pulled the ECU connector and performed all of the circuit tests described in the rennlist bpanders link above. Was hoping for a smoking gun test result but everything checked out. (Although I'm still questioning CHT reading of 2,250 ohms @ 78 degrees F. Seems a bit high to me.

So now I'm down to one question that perhaps the group here can help us with:

In rebuilding the MPS, reestablishing the height of the center plunger involves an imprecise measurement. So this could be the issue. There is mention of uncovering the adjustment screw and then calibrating the MPS. But Mr Anders says this requires special equipment. It seems like this adjustment could easily impact the rich/lean situation. Has anyone tackled this calibration without test equipment?

Again, sorry if this is a hijack but hope our shared experience helps someone now or in the future.

Good luck!

Ron

[rjames]

Calibrating the MPS correctly requires being able to know what the AFR is at idle, part load and WOT.
It could be said that fully dialing it in requires an inductance meter, but it isn’t necessary to get the car running well.

Fix/replace faulty FI components, don’t just bypass them. They are there for a reason. For example, removing the decel valve will shorten the life of the MPS diaphragm.

[brant]

Calibrating the MPS correctly requires being able to know what the AFR is at idle, part load and WOT.
It could be said that fully dialing it in requires an inductance meter, but it isn’t necessary to get the car running well.

Fix/replace faulty FI components, don’t just bypass them. They are there for a reason. For example, removing the decel valve will shorten the life of the MPS diaphragm.

(IMG:style_emoticons/default/wub.gif)

(IMG:style_emoticons/default/agree.gif)

[jrmdir]

Thanks for the feedback. Just to be clear, I'm in no way advocating permanently removing components. This car is still in the ER as far as drivability so I wanted to rule out things before buying parts. My decel valve is toast - stuck shut - so "bypassing" it was more because I took it off to get to the MPS and didn't feel the need to bolt it back on just for appearances. Easier to plug the line. I will spring for a new one once I can get this car on the road long enough to actually have a deceleration event (IMG:style_emoticons/default/smile.gif)

I removed the AAR to test it and found that the unobtainable (AFAIK) rubber "Y" pipe between the manifold and AAR was also toast. Again, easier to cap the manifold nipple until I can find a way to re-plumb. Probably run a straight hose from manifold to AAR and find another vacuum source for the small hose that is supposed to operate the devel valve.

Finally, chasing a rich mixture it's advised to make sure the cold start valve isn't leaking or being opened when not needed. I.E. colder than 40 degrees while starting. So, to me, bypassing in this case was a no brainer. Since there has been no improvement I'll reconnect it at some point.

Thanks once more for the great knowledge base that makes up this forum. Without support like this I'd probably have already given up.

Ron

[Dave_Darling]

Also worth checking the fuel pressure. Should be right about 29 PSI while the fuel pump is running. Higher means a richer mixture, as more fuel is being pushed through the injector valve per millisecond that the valve is open.

--DD

[r_towle]

Clean the inner parts in the distributor.
The advance plates stick in the wrong position after 40+ years.
Remove, clean, re-grease.
Costs 0.05 cents

[Halfnelson]

Thanks for everyone's feedback on this. I've finally got an update on things. After a couple of false dawns I'm hoping we've nailed the issue. Total work included:
Checking MPS - OK
New fuel lines, filter and fuel pump
Sorting the ignition as the spark was weak - so new coil etc
Going through all wiring and fuses
New CHT sender
New plugs for injectors

My guess is multiple small faults adding up to a lot of head scratching when we thought the problem was solved... only for it not to be.

Done a few local trips including a car show at the weekend. Fingers crossed now for a longer test drive.

[Rand]

I would have bet MPS. How was it tested?

A simple test: With car running, pull the hose off the MPS (at the mps end) and tell us what happens to the RPMs.
(Actually, that's a good checkup for all of us DJet users to do every couple years.)

[Halfnelson]

OK - so not sorted after all. (IMG:style_emoticons/default/headbang.gif)

After about half a dozen test drives with stops, restarts, refuelling etc went down the road to today, car stalled at junction and refused to restart. Strong petrol smell. Disconnected injectors and it would at least try and start but still lots of fuel still coming out of the exhaust so recovered home.

What's adding all the excess fuel with the injectors disconnected? Could the cold start injector be faulty?

[Bartlett 914]

OK - so not sorted after all. (IMG:style_emoticons/default/headbang.gif)

After about half a dozen test drives with stops, restarts, refuelling etc went down the road to today, car stalled at junction and refused to restart. Strong petrol smell. Disconnected injectors and it would at least try and start but still lots of fuel still coming out of the exhaust so recovered home.

What's adding all the excess fuel with the injectors disconnected? Could the cold start injector be faulty?

I would suspect an intermittent CHT or simply a poor connection with it

[Halfnelson]

Thanks Mark - have replaced the CHT but will test that again and also check the connection.