I'm about to embark on an MPS adjustment adventure to try and get my 1.7 to run better. (don't worry, the MPS I'm adjusting has already been opened up and tinkered with by a previous owner)

I have an LM-1, and will be using it to assist in my adjustments. I have already read pbander's MPS page, so I know what to adjust. What I don't know is what the type 4 "likes" in regards to mixture. I know 14.7:1 is stoichiometric, but I've already discovered that at idle it seems to prefer 13.5 to 14 to 1. (richer)

Does anyone have a recommendation for target AFRs for cruise, mild acceleration, and full throttle acceleration? I'm shooting more for economy and safe running temps than peak power. It's a street car, and a daily driver.

full throttle you want 12.5:1 for max power. Everything else you will want as lean as you can get away with for fuel economy reasons. Of course, lean is relative when you talk about a type4. My engine doesn't like anything leaner than about 14.5:1. Anything leaner than that and it will let you know (pop, spit, buck). So even my leanest settings would be considered rich (richer than shoich) by normal ICE standards.

Cool, Thanks! Just what I needed to know. My full throttle right now is really close to 12.5, so I won't really need to mess with that. My cruise and light acceleration are around 16:1 right now. (urf)

When you get done with that one, wanna check out the red car? I'd love to get it dialed in.

My car runs pig rich but really strong and hasn't fouled any plugs or diluted the oil or any of the bad stuff people talk about. It idles around 13 to 13.5:1. Full throttle is 12.5:1. Part load varies a bit but I tried to get it to go from about 14:1 at light throttle to 12.5:1 full load, with most of the inbetween range around 13 or 13.5:1. It runs great! On overrun I get some little backfires, but it could be a small exhaust leak or maybe the mixture is still too rich there. I am running Megasquirt as you know so I have full control over everything. I'm not sure how much control you have with the MPS to independently set full throttle without changing part throttle, etc.

Sure, as long as you have a bung hole. That goes for anyone else in the area as well.

Wait, that didn't come out right at all.

Um, let me think on it.....I'll get back to you........

Just for clarification... Bung hole and bung... plug

Ok, I've gotten things pretty well dialed in, at least in terms of driveability. I don't know what mileage is like yet, as I haven't driven it much.

It's doing something a bit odd though... The mixture seems to be RPM dependent. The way I have it adjusted now, it's about 15:1 at 2000 RPM, 14:1 at 3000 RPM, and 13:1 around 4000 RPM. Is this normal? If not, what would cause this effect? I did open up the MPS and found that it has the stainless steel aneroid cells, but the diaphragm looks to be copper. Could this cause this effect?

I did make sure to hold the pedal steady while I got this data to prevent the acceleration enrichment (throttle switch) from skewing the numbers. It's a 1.7 with 1972 d-jet.

I bet that is somewhat normal. I think the mixture should be richer at higher RPMs, I think it is supposed to be proportional to HP. Your case might be a little extreme though, but how is drivability? If it's ok I'd say dont' worry too much about it...

You can unplug the throttle switch to reduce the chances of accel enrichment screwing up your readings. The car will still run ok steady state, just not accelerate as well.

I've done lots of tinkering, including switching to another MPS that has the copper diaphragm. I'm still getting a light load low RPM miss (2700 RPM and under) that can't be normal. It's not the throttle switch, as it still happens with it disconnected. When it happens, the mixture goes lean, about 16:1. What I don't know is if the miss is caused by the lean mixture, or if the lean mixture is caused by the miss. (well, the indication of a lean mixture)

I can't think of a single thing that would cause a lean condition or a miss only at low RPM and light load. Any ideas out there?

I struggled with the same symptom last fall, only I didn't have a lambda sensor. I finally addressed it by putting a 270 ohm ballast resistor in the line to TS2. I'm sure I didn't solve the problem- only addressed the symptom. I'm probably running rich somewhere else (or maybe everywhere else) across the RPM/manifold pressure range, but the car is running pretty sweet these days.

When I get my lambda sensor- probably in the fall this year- if I measure a similar situation to yours, I'll probably start with the MPS. If you loosen the inner adjustment screw, you richen up at part throttle AND full throttle. You can then compensate by tightening the full load stop to bring the full throttle AFR back into line. Check idle, and adjust at the ECU if you have one that is adjustable.

The other "adjustments" are the ballast resistor value, and/or fuel pressure setting.

Also, it would be really interesting to know AFR, RPM, as well as manifold vacuum for each data point.

Good luck! Keep us posted,
Jim

i'm about to embark on the mps modifications to change my stock 1.7 d-jet to take the new 2056. i'm switching also to the 2.0 injectors, manifolds ect... is there a thread with walk thru directions on physically setting the m.p.s.? did you also bump fuel pressure to help out mixture at all?

mike

if the AFR is running a nice 14to1 and it jumps to 16to1 you might have a injector thats not firing properly. check the grounds junction first.