Ok, car is running great, but it just wants more fuel than my mps can give. It was almost there before I upgraded to the 2056. I have the mps maxed (inner screw all the way loose, won't go any further). I have the full load stop set at 3inhg and the part load kicking in at 7.5 inhg. I have now been inching up the fuel pressure, at 32 now, but the idles is now so rich it is bothering me.
The ecu idle is full lean.


The fuel injectors are 2 years old fj67s. Pbanders states you should be able to run up to 2.2l on d-jet without a problem.

Did I mention I hate pulling injectors?

Car idles great and the cylinders are all equal as far as what the plugs look like. 1000 miles on the top end rebuild. CHT temperatures are going lower and lower as I have been richening it up. I now rarely hit 370. 70 cruising is 350, even less when I am trying to be nice. Oil temps is still great, mostly because of tangerine racings oil cooler bypass. Night and day predictable temps since I installed that. Can't recommend enough. 5 stars.


Could all the injectors have crudded up equally? This would have happened before the rebuild. Since I started the richening earlier this year.

New fuel filter installed 2.5 years ago when I bought the car. New injectors installed after that. Previous owner had a rich condition (mps shot).

Watching the fuel pressure while I drive shows no change, sticks strong at 32 psi.

This plug has 200 miles on it.
Click to view attachment

Djet , properly tuned, can run up to 2.4 racing. Both on a dyno and track.
155-165hp depending upon the dyno.

I suggest getting an O2 sensor, stuffed up the tailpipe, hooked up to an AF gauge. This is temporary.

I run long wires up into the car so I can read it while driving.
Idle means nothing…you need to tune while driving with djet, or on a dyno

Add in resistance to the CHT circuit, this will enriched the mixture to the overall AF mixture.

Todo this once, and really precise.
Add a POT inline in the CHT circuit.
A POT is an old school volume knob rated up to 3-5k ohms.
Use the pot to get exactly what your motor wants.
Then measure across the poles on the pot and replace pot with resistors to match your specific settings.
Your settings, your timing advance, your motor, your elevation….all of that matters.

Hard fast test.
Take wire off CHT
Ground wire
Drive car full rich (which is wrong….but you can use this info)

You want to end up 12:1 for summer track time to help keep it cooler.

This is a pretty binary system that is tuned or not.
Once you set this resistance and AF ratio….it’s done.
Timing….you can mess with that by a few degrees…that is it

Leaks matter too….air leaks

I have the AFR already, a vacuum gauge, cht, and oil temp of course. The fact that it should handle far more than I have makes me worry about some other issue. Before I pull all the injectors I want to know if this is the sign of something else.

I have the right resistance on the cht headed to the ecu. I have pots up the wazoo (guitar player) so if it comes to that it isn't an issue but I shouldn't have to do that. I am a hair worried something bigger is going on.

Maybe I will just have to sonicate the injectors. Those elbows make me nervous, even new they are just a pain.

Oh, and as far as the afr, all looks good. A little rich actually, particularly at idle, less than 12inhg and greater than 5 inhg. I have a new o2 sensor coming Wednesday just to make sure.

Idle is useless, it’s a different circuit or AF map in the ECU
If you ground out the CHT wiring it will tell the computer it’s cold.
It’s typically sending 2-3k cold and under 1k when hot
If you tell the ECU it’s cold, it will add more fuel.

Check fuel pressure . Sadly I have fixed four fuel systems this year.
Check pressure when running.
Check pressure when you turn it off….watch to see how long it takes to drop.

Extra fuel pressure can help make it run richer.

Timing, too much advance will make it run lean.
Sticking advance plates can make it run lean
Point screw too long can jam advance plates and make it run lean

The one other trick is leveraging the cold start injector on an as needed basis this should not be required on your engine.

You don’t have a ton of variable here with djet
MPs tuning
CHT tuning
TPS test and verify
Timing, go look again

Air leaks…

123dizzy, so no plates or trigger points. It's d-jet so air leaks aren't really a thing. Idle mix is an issue since I have the mps fully rich. I have the tangerine racing tunable mps setup and as you richen the mps you will see the idle mix move. The ecu dial is an extra add on top of that for setting idle
Mix. Now, maybe my ecu is borked but that is how it works on my car. It would be interesting to know if that's how it works on others that can change their mps settings while the car is running. I am sure it is since a failed mps causes a rich idle as well.

Since the MPS has the Tangerine Racing tunable MPS setup it has likely been rebuilt, but do you know if your MPS has the "Spacer Ring for MPS Diaphragm" in it? If it is an MPS originaly from a 1.7 it needs the spacer ring for use on a 2.0 or larger engine. I ask this because you say this problem existed before the top end rebuild and this would explain why you can't adjust it any richer.

Just a thought.

Yeah, it's all 037 matching. I rebuilt it. Before this issue started I could richen it to the point of badness. That is why I am starting to convince myself I have to pull an injector. I should have checked it when I pulled the engine.

So....

I think I have come to some conclusions.
Installed a fresh o2 sensor.
Was rich and nasty except between 15inhg and 10inhg. By rich I mean pegged on 10:1, between 15inhg and 10 it was 16:1 and worse. So I said "screw it", I was going to stop chasing that 15-10 range and just set it so idle and wot were not pig rich. I had the inner screw full out and 32 psi fuel pressure.

Set the fuel pressure to 29, set the ecu to the stock notch. Then tightened the mps inner screw until I had 13:1 at idle. Disconnected the vacuum advance and plugged the port. Idle is at 850 hot.

Car was running between 12 and 14 for 20-15inhg and 12-13 9-0inhg. Wot was a healthy 12. Still lean 15-10 inhg. 14.7-17.

I mapped the inductance of the mps across the whole range and nothing odd is going on, only bit that bothers me is that the jump as it heads to 7inhg where it goes into full load operation isn't big. But my problem isn't there. It's where things are still supposed to be linear.

What would cause a lean condition right at 15-10 inhg. Throttle is cracked a little at that point, like a small hill in 4th doing 45. My car pulls 22-23 inhg at idle hot, cruising in 4th at 45 on flat ground I pull 20inhg. The port for the advance is still plugged. 123dizzy.

Car runs great. Pulls like a champ. Puts you back in the seat. Cold start is great, hot start is great. Aar works perfectly.

I've been told that the MPS outer screw should begin to engage the part load stop somewhere between 5-7 inHg (when starting from inHG).

I think the location of the outer screw can have a significant impact on the AFR, and getting that right may be part of your equation (if it's not something unrelated to the MPS).

Per Anders' MPS documentation, tightening the outer screw independent of the inner screw will enrich the part load mixture (however, it doesn't say if it's linear across all part load inHg measurements):

Under part-load conditions, the bottom of the outer screw is held against the part-load stop by the pressure differential across the diaphragm. If we tighten the outer screw independently of the inner screw (meaning we prevent the inner screw from turning with respect to the body of the MPS), the middle of the diaphragm is moved away from the part-load stop, decreasing its throw, and decreasing the amount of enrichment under full-load operation. Additionally, tightening the outer screw independently of the inner screw has the same effect on part-load operation as loosening the inner screw, enriching the part-load mixture.

Exactly. I spent hours the other day trying to move that abrupt change in inductance into that 10-15 spot but it just wouldn't budge. I found that it tended to flatten the curve rather than move the curve where I wanted it. Maybe I will give it another try. I hate messing with the outer screw because it affected everything. Particularly the full load stop. You really need to do that on the bench rather than in the car. Maybe I will muck with that in the car and if it works on that 10-15 I will pull it and reset the full load on the bench.

I cranked on that outer screw today while holding the inner steady. Probably 2 full turns (checking for change after each half turn). Nothing. Maybe moved it a hair lower inhg. So now it gets lean at maybe 13inhg and carries lower but lean it gets and the leanness is the same. Now I am really focusing in on how it changes with that vacuum at different rpms. I am also thinking about loosening the outer screw to see if it moves that lean spot to even higher vacuum.

My experience is that the full load stop screw will also impact part load, depending on where it’s set.

at this point I am starting to consider chicken sacrifices.

Have you grounded out your CHT wire?
Does that change your AFR?

The system is designed for the engine to run lean at part throttle. You should stop trying to make it rich in that MAP region.

Yeah, cht works as it should. Chris, I was suspecting that is what I should do, I was getting some lean bucking at part throttle when cruising so I was worried. After my "reset" and the little tweaks today the lean miss is gone as far as I can tell. Max lean is 16:1 at that part throttle cruising. I haven't taken it out for a run on the interstate in this configuration though. That's the part I worry most about. My plugs are still whitey white but maybe my new rings and guides just mean I am burning really clean.
Click to view attachment

I told you the trick.
Ground our the CHT
Make it richer.
Add resistors to that circuit to enrich it across the whole range.

This motor is not stock
Stock ChT might work, but you are missing the trick

Google it if you don’t believe me….it’s a pretty normal part of tuning larger motors

I would also focus on timing and the distributor curve.

Oh I can richen it up now, no problem, but then it is too rich everywhere but 14-9. I am now running great (a hair rich actually) everywhere but in that 14-9 range, with my MPS inner screw no longer maxed out.

Timing is always something to play with but I have mine tuned to a sweet spot (moving it either direction results in a much hotter head). I may tweak it again now that the MPS seems to be in a better place but I would rather not.

It is the abrupt change in the mixture as it hits the 14-9 range which leads me to think that Chris is right (of course), there is probably a built in (ecu) leanness at these MPS values.
Click to view attachment

I think we are there. This is fully warmed up after 20 miles on the interstate. Video is from the return trip home, vacuum advanced hooked up again. Running nice and cool, 72ish mph for the first half, then down to 55 a little after the middle. Still a hair rich at WOT but that is fine with me. Maybe I will screw in the full load stop a hair to compensate for moving in the outer screw. No bucking/lean misses.

https://www.youtube.com/shorts/rr1RwLEg0x4

Just took a look at my timing now that everything is running perfect. At 850 it's at 7.5 btdc and 27 at 3500. Of course that is all plus or minus whatever my marks are off. I turned back the outer screw almost a half of what I tightened it yesterday. Took it for a long drive. Was interesting, tried it with and without the advance and for once the advance made a marked improvement in smoothness of throttle response. I think everything is finally coming together.


I was asking myself about that timing technique for the d-jet .. after you put on a 123dizzy, is it really necessary to go with the 3500 or can you just use the low rpm timing? Anyone know why they had a different method for the d-jet?