In thinking about a supercharger on my 89 Raider with 91 Stealth engine, I am wondering how adaptable the MAF/ECM are. Has anyone swapped hte MAF out to a larger unit? Will the ECM learn enough to alter timing? I will go for different hi flow injectors & maybe a rising rate fuel pressure regulator. Checking 94 3.5L DOHC MAF specs right now...

Thanx..
Ed

AFAIK, no one here has tried a MAF swap. I would think that a different MAF would confuse the ECU, since most MAF control on early units is at idle and becomes less of a modifier as rpms increase.

I have no idea if the ECU can "learn" anything... I doubt it. I'd think it's only programmed to read signal input and adjust fuel and spark within the imbedded lookup tables. I'm not going to assume the ECU can handle anything over a 15% change from the normal range and have chosen injectors accordingly.

I've run my truck 5000 miles with an analyzer display beside me and can only say that the ignition timing is very much dependant on throttle position and engine loading. At full coast downhill highway speed, advance is 38-40*BTDC and at uphill/full throttle it declines to 15-17*BTDC.

Frank

I don't know about the Montero engine in this regard. However, just out of interest, I run an RX-7 MAF on my 1.6L Miata with the stock ECU, but the fuel system has enough reserve to handle the extra air at high revs (>6500 rpm)when the stock MAF would be restrictive (limit is 7300rpm). I have no problems with it. With a supercharger I guess you'll have to be careful that the MAF isn't reading at maximum before the max air flow from the supercharger is reached. Then you'll be lean <img src="/forums/images/graemlins/scared.gif" alt="" /> Might be OK at low boost.
A MAP sensor would be better if it can be hooked up to the stock ECU. A knock sensor would be good too if you're going down the FI road. Having said that I no expert on FI

The StarQuest guys swap a gen1 DSM turbo maf into their systems, with only a connector rewire, but both are karman vortex counter types. I think we have hot wire mafs.

MAF's suck, both literally and figuratively. I think it would be as easy to swap in a Megasquirt2 and go speed density instead of mass air as a control regime, and just lose the MAF and it's flow restriction entirely, and run off a MAP and TPS instead of MAF and TPS. Simple sugars are sweeter.....

Reuben -

The use of a rising rate regulator can compensate and provide needed fuel, provided it is properly tuned. From what I've read (not really experienced), these early MAFs don't have much influence on mixture except at/near idle.... I think they mostly tell the ECU that the engine has little-to-no load. As the engine draws more air, I think the MAF output signal decreases - or is ignored by the ECU with increased rpms.... whether these MAFs have more influence on fuel mixture or ignition timing, I don't know.

I'd think that the 3.5L MAF might be ok on a 3.0L so long as the signal voltage is the same at 3.0L and/or 3.5L idle - and the curve is linear as compared to the 3.0L MAF. If the 3.5L MAF reads the smaller air flow of a 3.0L at low speed operation, it could be harmful to a 3.0L and cause a lean idle - but that could be corrected with the regulator by raising the base fuel rail pressure to compensate with more fuel - or with larger injectors at the same pressure.

I suspect there could be a benefit of less air flow restriction, but I want to stay as close to stock initially and make incremental changes to see what happens.

Frank

You're right Fank. When I wrote my post I was thinking the whole time about the 'barn door' style MAF that I have. Once the door is wide open under high load that's it, additional air flow will not effect the signal to the ECU and so the mixture would lean out. Since it's NA this won't happen, but if I stuck a SC or turbo on there with >7-9psi of boost that could happen. However, a hot wire style MAF (is that what the stealth engine has?) may operate differently, but won't it will still have a limit in the amount of air flow it can measure?

The other issue is the Miata engine is a turbo engine made NA. It has strong internals and oil cooled pistons. May be the Stealth engine is the same, I don't know. In any case and air/fuel ratio gauge and/or a knock sensor may save the engine if this is going to be an experimental project. I've been thinking about a Megasquirt unit (looks like fun) and I think you're right that a 'piggback' unit to retard timing under boost won't be too difficult to tune. I have heard that the stand alone units are much more involved but quite doable. Having said that an MSD timing retarder unit would probably work well too.

Like I said I'm no expert on this, but we have probably all heard about DIY FI projects resulting in a blown engine. May be a 3000GT/Stealth forum would be helpful in determining what the engine can handle, unless you all already know that <img src="/forums/images/graemlins/pfft.gif" alt="" /> and I just talking out of my...

Reuben -

I don't know what sort of MAF is on the Stealth engine.

The Gen1 ECU does a pretty good job of retarding timing under load. <img src="/forums/images/graemlins/cyclops.gif" alt="" /> In NA form and with a healthy engine and good gas, I don't think you'll ever hear a spark knock from one.

A boost-dependant rising rate regulator provides needed fuel under boost by increasing fuel pressure, which in turn increases fuel supply without the ECU knowing why - only that the mixture is ok for the operating parameters. On a lean o2 sensor signal under boost, the ECU doesn't know that fuel pressure has increased and keeps increasing injector pulse width (if necessary) until the lookup table is maxed out or the injector goes to max flow. The trick is to choose an injector size that gives good idle characteristics, yet can deliver enough fuel without asking the ECU to exceed the imbedded range of lookup tables in the chip. It's up to the tuner to find/adjust the rate of fuel pressure increase that satisfies the mixture over the boost range - a blend of injector size, base fuel pressure and rate of pressure rise with increasing boost. I'm no forced induction FI expert either, but I'm about to start school on my system.

Frank

All interesting points Frank. It'll be fun to see how this project develops <img src="/forums/images/graemlins/kewl.gif" alt="" />

I just caught this as part of the megasquirt thread.. Forgive me for not knowing the Mitsu...

A rising rate fuel pressure regulator is a patch. It's better than nothing at all and is functional, but because it has a linear response, it can only be tuned for a specific throttle/load/pressure setting.. that's usually WOT. Below that, it's likely to influence how your motor runs on part throttle and the stock ECU may or may not take kindly to more fuel.. There's a limited range of adaptability.

It's a good first step.

If you're going to consider MS, the *hardest* part of the entire deal is figuring how how to do the spark. Work that out and fuel is cake!

Hi, Darin -

Thanks for checking in..... visited your engine rebuild pages.... very nice work! <img src="/forums/images/graemlins/kewl.gif" alt="" />

We don't have too many options (as in none) for the Mitsu 3.0L, so we constantly complain about a lack of power. <img src="/forums/images/graemlins/lol.gif" alt="" /> I'm trying to correct that power deficiency with my own concoction - inexperience and all. Here's the link to what I'm trying to do:

Link

Feel free to criticize on that thread. <img src="/forums/images/graemlins/cheers.gif" alt="" />

Frank