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 ChrisClick to view attachment

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

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

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

That is a beautiful car!

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

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.

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

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?

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

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.

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

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

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

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

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.

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.)

OK - so not sorted after all.

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

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

I had a similar situation and it turned out to be a bad ECU. After 15-30 minutes of driving, the car would run super rich.

I still question your rebuilt MPS. You said you tested it, but just verifying that it holds vacuum isn't enough. You need the tools to adjust it (tangerine racing) and an AFR meter to dial it in. If the rich running your experiencing is intermittent, than you can probably check the MPS off of your list. But if it's always rich and swapping the ECU out doesn't change anything, then I suspect your MPS needs calibrating.

@jrmdir At the very least you need the tools to adjust the MPS and and an AFR meter to set the MPS correctly.

Thanks Robert - the MPS hasn't been rebuilt, still the original and holds vacuum - or at least was. Will double back and recheck.

How did you diagnose that it was the ECU? There seem to so many potential culprits and I had hoped these were already ticked off the list.

My mistake- I thought your MPS had been opened up.
I figured out it my ECU was bad after testing all of my other components and eventually swapping it with a known good ECU. See if you can find someone who will let you borrow theirs. You're lucky in that there seems to be a ton of used 1.7 ECUs for sale at any given time. 2.0 ECUs can be hard to find.

What was the difference in idle when you pulled the hose off at the MPS? Just give me that.

Would it even run? IIRC, pulling the hose off would just cause it to go super lean, so if it ran I guess it would tell you that something else in the system is causing an uber rich condition, but it wouldn't rule out the MPS as a contributor.
If it doesn't run, what would that tell us?

If it's an intermittent issue or doesn't happen until the car warms up a little (I'm still not clear if that is the case here) then it's probably not the MPS. I haven't run across intermittent issues, or issues that happen only when the engine is cold or only when warm that ended up being the MPS. Seems like when it's the MPS that's the problem, the symptoms there all the time.

Just out of curiosity, have you checked which injectors are in there? Mine came with 1 1.7 injector and on a 2.0 that means one really lean cylinder. Some fool might have put 2.0 injectors in yours.

OK - I'd never even considered the injectors could be wrong but...

Click to view attachment

Lots of questions spring to mind like how it was even running with the wrong injectors in?

The number seems to end 1120 07 (although I couldn't quite see) - which doesn't look like 2 litre green injectors?

Next step is where can I find either the correct yellow injectors or a new set of compatible alternatives?

I have 1... And it is yellow.


I bought those new injectors, Standard motor products. The guy that rebuilds injectors tested them and found them to be quality. Not sure what the 1.7 version is labeled as. Fj67 is the 2.0

Click to view attachment

The left side is the 2.0

Wrong injectors.. amazing! I bought a set of Standard Motor Products injectors for my 2.0 Outlaw and they sure look nice. Get them if you can't find OEM yellow injectors. RockAuto had the best price I could find.

Those look like 1.8L injectors, for L-Jet. Someone had to mess with the wiring harness to use those.

Wow, the plot thickens.

Pulling the MPS hose does NOT cause lean, it causes full RICH. True, it should not run, it should immediately choke and die. I wasn't necessarily suggesting the MPS as the problem, but ANY time Djet runs rich, check the MPS because a bad diaphragm or leaky hose/connection is a common cause of running rich! I can't think of another test that takes two seconds that tells so much about fuel mixture. IF it didn't change, it would have absolutely been MPS (or not) in 2 seconds! Always do the quick tests to quickly rule things out in early troubleshooting!

Yup- I had it backwards. After all the DJet and MPS troubleshooting I’ve done in the last two years I don’t know how I got that one wrong!

We've all gotten things wrong. My biggest point, is quick troubleshooting. I've seen people spend hours chasing rabbit trails that could have been ruled out in seconds! It hurts every time.

PS: Checking out your music

My guess is not 1.8 as they are more of a blue / green IIRC but also the whole shape of the injector plug looks different to the 2.0 and 1.7 injector plugs. Could be someone try to find a suitable alternative or ordered the wrong part? The FJ67's etc aren't available in Europe.

The one you are looking for is the fj114. 59 dollars on Amazon.

I'm resurrecting this thread if that's ok so hopefully it'll add some context / back story.

The gist is my 73 1.7 on standard Djet would run ok for a short period of time - then flood. It was an intermittent problem that got so bad petrol is now actually spewing out of the exhaust.

After discovering I had the wrong injectors fitted (way too much fuel being delivered) I had a set of new FJ114. I hoped this would crack it - but after starting and ticking over for a short while... it started to run rough, smoke cough and die. Turning the car over then results in petrol spewing out of the exhaust again.

Short recap of work done includes: all new vacuum lines, CHT sensor replaced, MPS tested, fuel return tested, cold start injector disconnected and bypassed, new fuel pump fitted and fuel pressure tested, new coil fitted.

The question is - a year down the line - what next? And what could be causing such a catastrophic over-fueling - it's not just running rich - there is fuel pissing out

Have you checked your CSV for leakage?

I spent well over a year troubleshooting a similar issue. The car would run fine for a while, and then out of nowhere, go rich and then stall. Right before I figured out what it was, the amount of time it would run well before stalling decreased.

It turned out to be a bad ECU- the things that rarely fail supposedly. I think it was a heat issue. As the engine bay warmed up something in the ECU would fail and cause an overly rich condition. Figuring it out wasn't easy. I had two other ECUs that I used for testing and both caused the car to flood- including a NOS unit that had never been installed. A 3rd ECU I tried out of desperation fixed the issue, and have had no issues since installing it 2 years ago.

It's an easy thing to rule out if you have another known good ECU you can swap in for testing.

You mentioned before that you had disconnected the injectors and were still getting fuel, the cold start injector is the only other source for fuel.

Thanks for the ideas - yes, we have bypassed the cold start injector.

No it won’t, going on ten years and 40k miles, deaccl valve is a stop gap pollution device pretty much ruins engine braking.

Yeah, check that cold start valve.

Any chance you can borrow another ECU? (another quick and easy check if it is available).

I have to suspect soemthing catastrophic with something like the csv. Even max rich by the ECU wouldn't cause what you are experiencing. I seriously doubt your brand new injectors are stuck open. as stated above... it's the only other thing bringing fuel. You could block the csv fuel line (super easy) and give it a go.


Not even sure the trigger points or malfunctioning 123dizzy could cause this either.

The CSV should have been done - but I'll double check as that makes sense. Also, will try and borrow an ECU.

Pull one side of the fuel rail off while the engine is running, note the amount of spray, at idle it should be minimal, if the injectors are just open the ECU is at fault.

You mean the injectors right? Make sure you put them In coffee cans too. Double check that csv first since it is easy. Have you checked your fuel pressure recently? On the rails?

Two other things to check:

TS2 - cyl head temp sensor. It can fail to dump enough fuel not allowing it to start, perhaps yours is intermittently failing.

MPS - check its ability to hold vacuum. Does it hold up to 18 inHG steady, or is there a vacuum leak? When the diaphragm fractures it fails rich. No vacuum or a rapid vacuum loss will be very rich.

@emerygt350 Not true. What he is experiencing is exactly what the bad ECUs I had did, and all were the correct model for my car.