What's your A/F on Overrun?, 'Nother D-Jet A/F Question Options

[BeatNavy]

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?

[mgphoto]

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???

[BeatNavy]

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

[mgphoto]

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?

[BeatNavy]

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 (IMG:style_emoticons/default/confused24.gif)

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.

[mgphoto]

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 (IMG:style_emoticons/default/confused24.gif)

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

[BeatNavy]

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.

[falcor75]

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?

[r_towle]

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

rich

[BeatNavy]

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.

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?

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.

[brant]

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 (IMG:style_emoticons/default/confused24.gif)

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.

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.

[BeatNavy]

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:



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.

[BeatNavy]

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.

[Olympic 914]

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.

[BeatNavy]

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.

[saigon71]

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).

[DRPHIL914]

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

[BeatNavy]

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

[Mark Henry]

Does A/F on overrun even matter?

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.

[Olympic 914]

Does A/F on overrun even matter?

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