For those with D-Jet, what are you typically seeing for A/F ratio on a medium to hard overrun? Based on what I've read here mine seems too rich - like in 10's and 11's. Once the RPM's drop closer to idle it bounces back up to normal idle A/F ratios. Does A/F on overrun even matter?

What does your exhaust sound like???

Good. No popping, if that's what you're asking. It doesn't "sound lean." I've had that in the past..

No poping right, not lean.
Best thing for type iv is not lean. Next issue is gas mileage, are you happy with the number your getting?

Not particularly. That's sort of been the root cause of my continuous futzing with D-Jet recently. It runs well, but mileage is not great best I can tell. With 2056 I've never got better than 20 mpg driving to/from work -- 20 minutes of "parkway" driving which is 95% of what I do. I maybe got closer to 23 to 25 last year going to and from Hershey on the highway. Maybe that's all I should expect

I've swapped out different combos of CHT and with and without spacer recently, and I got leaner, and hotter, after removing the spacer, but interestingly the mileage didn't seem to get better. The spacer I had on the CHT was long - like 23 mm -- and seemed to act more like a ballast resistor and enriched mixture even after warm-up. Today I cut the spacer down some to try to allow good warm-up while still allowing the CHT to get to "operating temp" that's not too rich or lean.

I may be chasing a couple of minor issues...but I wanted to see what a "normal" overrun A/F would be as this hasn't really changed with all the screwing around I've done.

The issue is not your temp sensor, it's the mps, it must be adjusted correctly.
Temp sensor is measured by the ecu and compared to a set resistance within the ecu.

Spacers just try to compensate for the cold head, hot engine problem. Opening the throttle with get her started.

You are just going to chase your tail following the resistor - fuel pressure route.

If you can adjust the idle with the "pot" on the ecu your tps is adjusted correctly, 1/3 of the battle won.

The best way to adjust the mps is an Air/Fuel mixture meter and the Racer Chris mps kit.


A correctly adjusted mps with your engine combo, 24 mpg is not out of reach.
Even with a certain amount of aggressive driving style!
Mike

I've also spent a lot of time messing with my MPS (I have two of the 043's to play with). Both have been repaired with Chris' kits. I have spent hours getting the numbers to match Brad Anders' numbers as close as possible to include graphing them out on Excel to get the slope / range as he did. Funny, I could never get the 0 psi number (WOT) to even get close to his. Full load stop wouldn't adjust that far out.

But as I've said, overall the car runs great. I was just curious if a rich overrun would point to something else going on, or if those numbers are typical. Nobody has any values to throw out there?

Thanks, Mike.

Could leaking injectors cause your WB to read rich on overrun?

One or two injectors drips a bit....the fuel vaporizes in the hot cylinders but doesnt burn...WB reads this as rich condition?

have you ever replaced the cold start injector? They leak.

rich

Hey Rich. No, I haven't. Hmmm...maybe I'll pull the fuel line on that and see what happens. Perhaps after the blizzard and arctic hell that hits us this week is done and gone.


Something else to check. I have a set of recently serviced injectors. Maybe I'll swap those out.

Thanks for the suggestions. It's just one of those things where I know I'm leaving something small on the table - a little mileage efficiency and/or small amount of HP - which implies something is not configured or working correctly. And that annoys the crap out of me.

just a point of reference
and I'm not 2056, but rather the stock 1994cc(?)

but I'm averaging 31mpg highway with stock Djet on a stock motor
I purchased the motor used and was told it has a F.I. cam
but really its stock as far as seat of the pants dyno
I did adjust the MPS for richer numbers on this motor using an AF meter

just a point of reference.

I did some more looking around today, and I think my throttle shaft is sticking in the throttle body and not returning the TPS to the idle position fully, especially when the overrun is over 2,000 RPM. As it drops below 2,000 RPM, I get A/F numbers more like idle (~13.5). Not sure if the higher vacuum level at higher RPMs is ever so slightly preventing the throttle plate from closing fully, but I pulled the body and TPS to check it out:

Click to view attachment

As I understand it, in order to be in the idle/overrun "circuit," there needs to be continuity between where the two arrows are pointing in the picture above - the little arm (where the smaller arrow is pointing, the fuel shut-off switch) and the pin (where the larger arrow is pointing). The middle "wiper arm" also needs too be on the idle trace on the board. The only real difference between idle and overrun is the ECU will shut off fuel delivery at RPM's >~2,000. Is my understanding correct?

Even after careful adjusting of the TPS I find there's too much play in the switch/throttle body shaft to reliably ensure continuity unless the throttle is really fully closed. May need to overhaul the throttle body.

I'll probably also try plugging off the cold start valve fuel supply to eliminate that as a possibility.

Not this. Pulled the fuel line that runs to the CSV. No change.

Did you ever find out any more about this ?

I am also seeing rich AFR numbers on over run, same as yours 10-11

Mine is a 2056 with djet and seems to be similar to your build.

running a 043 MPS with initial settings at the 037 specs since I have a 037 ECU, but it was much too lean at those settings. Now I am in the neighborhood of 13.5 - 14.0 at a 3000 rpm cruise but going down hills on over run it goes to the 10.0 - 11.00 range.

I did set the throttle switch originally and reset it when I had the throttle body off for another issue.

haven't checked the mileage yet and only have about 400 miles on the rebuild engine.

No, not really. I did refurb the throttle body so I'm confident the TPS is going into the idle circuit. I also played with the full load stop and decel valve, but I still see the same basic numbers, including fuel efficiency. Not convinced they are related, but I would like to see what kind of mileage you are getting.

I can't speak to your A/F on overrun. I had my rebuilt MPS bench tuned by Jeff Bowlsby to 2056 specs over the winter and slapped it on. I don't think the car has ever run better.

But as far as gas mileage - what cam are you running in your 2056?

My combo runs 20-22 MPG around town and 25-27 MPG on the highway with a very mild FI cam (FAT 440 MP).

My AF seems to stay around 12.-12.5 I believe - depends on how the TPS is set, when I have is supposedly set properly so that I can adjust the mix on the ECU knob it actually goes way up high like 20, so I tweek it just a slight bit so it doesn't do this and then it hangs around the 11-12 something area. - but then its off the idle circuit that allows the idle mix to be set with ecu knob, - stock cam, stock 2.0 motor - I am getting over 30 mpg on freeway driving, @26 in town - Bob you may remember when I brought my car back from Chris's we went for a drive and it was bucking bacd- I replaced that TPS board and its as smooth as can be now- so the board is a good board,

Phil

Good question, Bob. In my case I am running stock cam.

Overrun and AFR means diddly squat. No load, it doesn't matter how lean it is.
I have complete fuel cut on my programmable FI, you can't get leaner than that, it's never hurt anything.

If it were lean I wouldn't worry about it, but its real rich in the 10.0 + range. So somehow it is dumping fuel in there. it may even be worse but my low reading limit on the Autometer AFR is set a 10.0

granted I have not put many miles on this engine and am still sorting things out but after following a truck down a long hill with it going rich, when the truck stopped at the bottom of the hill to make a turn and I had to stop behind it, the engine just quit... it did start right up again, but since I am looking for problems this might be one.

Engine is a 2056 w/ Raby 9590 cam and Ham's RS+ heads, SS HEs and a Triad muffler. ECU 037

Oh sorry, brain fart...guess I should read things better.
My first guess is it isn't dumping any more fuel in, just you cut off the air so it makes the charge rich. I'd say it doesn't have any fuel cut at all, I don't know if that is normal for D-jet or not.
I do know L-jet definitely has a fuel reduction, but not a total fuel cut.

It depends on the ecu for fuel cut off.

But it would be reading a sensor, either the TPS or the MPS.
Totally guessing but I'd say likely TPS.

IIRC D-jet is designed to cut off fuel on closed throttle until rev's drop to about 1200. then re-start fuel. Must be fuel leaks somewhere, or throttle position switch not fully to idle position

IiRC it is TPS Mark.

My understanding is that the TPS detects an idle situation and then mixture is controlled by ECU idle settings, not by MPS. Some ECU's cut fuel off above certain RPM on idle, although I can't remember which ECU models off hand. But I'm not going lean, I'm going rich. Mark's explanation about less air would make sense. But that would indicate a fairly normal operation, right? I was under the impression that most people see pretty lean conditions on overrun.

Rob

What ECU are you running?

You said that you checked your TPS and I have mine set per these instructions.

http://www.pelicanparts.com/techarticles/9...alibrate_20.jpg

Pretty sure I'm running a 043 ECU. Yes, I follow those TPS calibration instructions as well. My ECU is set for idle so I usually run 13.5 to 14.5 a/f ratio. I will verify which ECU I have....

I believe the overun or "with overun cut off circuit" are listed on Brad Anders site in his part description matrix.

I think it.s function is three fold. Driveability, emissions, and fuel economy.

I know I have it on my car. You can actually feel it when coasting to a stop when the tps hits the cut off. That is.....when it is adjusted right.

so you are saying the correct setting is for it to "cut out"? which would then cause the AF reading to go up considerably- which is consistent with my previous experience- when idle circuit is set so that the ECU knob will adjust a/f on idle , it is set in correct position, when it is, I will see the A/F reading go full lean, like 22. - how I have it set now it does not do that - but ive never seen mine go rich like a 9 or 10. I would recheck your TPS board at idle and does it effect a/f and idle when adjusting the ECu knob ?

I am saying that when the engine is under no load....why worry about AF. Because D jet adjusts mixture by vaccum signature from the MPS ....under decelerarion with the throttle plate in the closed position....the requirement of fuel is not meaningful....so why measure it? My answer would be that you are wasting fuel.

The ecu adjustment knob is to set the fuel mixture at idle only. Once the throttle plate is moved that no longer controls AF.

Just closing the loop. I actually have an 044 ECU, which has NO overrun cutoff circuit. So...based on that fact and Mark's suggestion that it's probably less air, not more fuel, resulting in a higher A/R mixture -- and would seem like behavior. But the point of my OP is that I'm trying to determine if my mileage is lower than it should be and, if that is the case, whether this could be a cause. Right now I'm guessing the answer is no...

Thanks for everyone's input.

Very early cars would cut fuel on overrun, but that function was eliminated. The literature I have read is "due to the uneven cooling in air-cooled engines, it produced higher emissions". I believe they removed it in mid-71 model year?

I can't access Brad Anders' site right now, but I suspect he lists when the change happened.

--DD

I can't see a system that has no fuel cut having lower emissions.

My bet is with fuel cut the car had more engine braking, eliminating fuel cut might actually have better MPG as the car coasts more if it's still burning a bit of fuel. Likely VW eliminated the fuel cut to increase the cars MPG figures. Without coasting you would be on the gas more when cruising, because of more erratic speed control, thus burning more fuel.

I see this in my bug (T4 conversion) that has full fuel cut, my engine braking is huge.
In fact I could see the Joe average driver not liking how much engine braking my car has. You can't lug my car, I have to keep the rpm up around 3K as the engine braking action makes it a PITA to cruise at lower RPM's.
You definitely wouldn't like driving it in constant stop and go every day.

Mark I agree, this is what I was seeing and why I readjusted my TPS so that it wasn't cutting out like that, and its much more smooth to drive this way, I have a good idle, no issue with the cut out, my mileage is excellent so I will probably leave it this way. I may not be able to adjust the idle with ECU knob but I don't need to , as the A/F and idle are perfect, having rebuilt then tweeked the MPS to get it where its at - .
BeatNavy doesn't have this circuit so its most likely very similar to the way I have mine set but I am still wondering about his issue having A/F showing increased richness in that situation. Please repost if you figure out the solution-

I was thinking more on what Dave said, although the emissions part doesn't make sense to me, the 2nd bit about cooling does. The rich fuel charge would definitely have a cooling effect on the engine heads.

I think this rich condition on decell is perfectly normal and what the creators had in mind.

According to Porsche/VW the fuel cut off caused the cylinder walls to get hot, no fuel cooling, when the fuel returned there were atomization problems causing the hydrocarbon count to go up, not good for the environment and counter to what VW was trying to accomplish with FI.

Back to the OP, I think you may have a problem with leaky fuel injectors, overrun is the highest vacuum, that could cause fuel to be pulled from the injectors causing rich numbers on overrun, as mentioned this will not hurt your motor at all but your fuel economy will decrease.


Check the condition of your spark plugs, color will tell you a lot.

Did you ever fix the problem with rich AFR on over run?
I'm running the same engine specs and had the same problem.
Car idles great but due to the needed MPS adjustments it idles rich 11,8 AFR, this is also resulting rich condition below 2600-2800 RPM 12,3 - 12,7 AFR all range above 2800 RPM is perfect.
I was able to improve the rich situation by adding and adjusting (Opening at 15,5 Hg) a Decel Valve. This improves drivability in low RPM range and also improves the rich overrun situation.

Cheers,
Frank

I played around with my MPS, decal valve, tuning and a host of other things since I originally posted this. Car runs great, idles well, and is blast to drive. But I still see AFR numbers in the 12 range during decal, and my MPG numbers are not great. For the most part, I've given up worrying about it much, particularly since I have plans for a different motor before too long.

All good

AFR of 12 will not hurt the engine and is reasonable I think. What MPG do you get?

Barely 20 MPG, driving mostly in and around my neighborhood and to/from work, which is mostly parkway driving - 55 mph for 2 miles, then a stop light - rinse and repeat. The few opportunities I've been able to track actual "highway" driving I MAY get closer to 24 MPG. Nothing close to the 30 MPG or more that many claim.

Thanks Rob,
this is what I get out too (20.5 MPG) but this is while driving it hard and still doing some minor adjustments.
Season is almost over, so probably no normal driving within this year...

Hi,
just saw this. A while ago I had a PM exchange with Brad Anders regarding the differences between each of the DJet ECUs.


This is a para phrase of what he explained to me, rgarding overrun cutoff and the 4 and 5 waveform generators.

Overrun cutoff ended up being a mixed bag with regard to emissions. Apparently, it doesn't work that well, something with regard to engine cooling. In the early '70's, before the 3-way catalytic converter became available, manufacturers were trying anything and everything to meet the new CO, HC, and NOx standards.

Perhaps he will chime in here.
Carlos

I also have played around with my MPS, and timing.

On decal I see around 15.0 + afr. I may be running a little on the lean side though.

But on a cruise the AFRs vary from mid 12s to high 14s depending on throttle position.

Do you have a meter to check your MPS values? I have notes around here somewhere with where I set the MPS on my car. Maybe we could compare settings.



Little different system since I have the 037 ECU

My Air/Fuel numbers are pretty good - similar to yours at cruise.

I've actually swapped out like four different 043 MPS's in an attempt to figure out what was going on. Last year I picked up one rebuilt professionally by that company back in the day (Fuel Injection Corp?), and I used that for a while. I assume it was calibrated to stock 2.0, but I didn't notice any real improvement in my MPG, although I was probably slightly lean at cruise.

Earlier this summer I picked up a stock, unmolested 043 that I wanted to use to baseline my MPS values on my inductance meter. That confirmed my suspicion that my (cheap) inductance meter provided significantly different values than those documented by Anders, particularly at part and full load (idle wasn't too bad). So I've used that stock 043 as my "calibration," and adjusted my other MPS to just slightly richer than stock.

I can definitely share my numbers, but what would probably really help is to let you use that stock 043 so you can also calibrate your inductance meter. It's my guess that different models/meters can vary quite a bit. Let me know if your interested.

In terms of my mileage, that remains somewhat of a mystery to me. It could be multiple factors. It could also just be what it is.

Hi Beat,
it is quite easy to adjust this 'late-type' TPS, because it has the integrated 'stop-sheet'.
No electrical measuring needed for adjusting it (just for controlling the functions...).

Just loosen the screws so far you can turn the body of the TPS without great resistance.
First turn the body counterclockwise to the stop (by the screws).
Then turn it clockwise till you feel the resistance of the brown plasic arm touching the 'stop'.
Fix it in this position without turning it back. There has to be some
preload.

As you mentioned, this type of TPS uses the contacts you marked for cutting off the idle signal. The position of the 'wiper-contacts' doesn't matter, this is pre-adjusted in the PTS by the position of the 'stop-sheet'.

Regards
Norbert