questions on maf, injectors, and a/f

jruppert · Jun 10, 2005

I have a 94 and had just sent my pro-m 77mm to professional mass air systems (formally pro-m) to get recalibrated for my 30lb injectors. I believe these are 30lb because they are red. Here is my problem. I install factory meter on and go into my tweecer and tell it to run stock meter with 30 lb injectors. The car idles fine until you take off and put load on it. At this point it goes way lean. It will idle fine and even if you rev it up it will run fine. I fussed with different meter files and had no luck. I even tried richening the meter and still no luck. Finally I told it to run 36lb injectors. Bam, it runs! It doesnt run perfect but it does run and stays consistently around 14-15 in a/f. Can anyone explain why this is? I was thinking maybe I was wrong and actually had 36lb injectors but called the company who is recalibrating and said these are 30. So what gives?

dcarlson · Jun 10, 2005

YOu recalibrate for the injectors twice. The meter was calibrated for 30 lb injectors, so it is sending a smaller voltage signal. The computer thinks it is a stock air meter with 30 lb injectors, so it is adjusting the way it reads the MAF signal and leaning the mixture accordingly.

You need to do one or the other, not both. Basically just go back into the tweecer and tell it you have the stock meter and the stock injectors. If the meter is calibrated correctly it will run fine.

jruppert · Jun 10, 2005

I tried doing that. I read eec and started a new file. I changed the c.i.d. to 342 and checksum to 0. It still wouldnt run. Maybe something is wrong with the meter too.

jruppert · Jun 10, 2005

Just out of curiousity.. Before I ever had a tweecer I was using the Pro-M 77mm calibrated for 24's with 24 injectors. I never used a chip or anything. The car ran its best at that time. Since I have went to larger cubes, better cam, better heads, larger injectors, tweecer, and it runs slower then before. So if I could run this meter with the 24's (and being calibrated), why cant I just use the pro-m (calibrated for 30's when i get it back) and the 30 injectors and not change anything in tweecer? I have never tried this but it seems like the same thing as what I use to do.

jruppert · Jun 10, 2005

Also, I just did a throttle conversion back to 86-93. I used a stock 89 throttle until my 75mm came in the mail. It was running fine until I installed the 75mm. This is when it threw it out of whack. I assume the more air made it run lean.

dcarlson · Jun 10, 2005

There is no reason why you couldn't run the Pro M calibrated for 30s with the stock computer. There are some fine tuning advantages and slight driveabilty issues that can be cleaned up with a chip, PMS, tweecer etc. but there is no reason it shouldn't run OK with just the stock computer.

I have talked with some Ford EEC IV & EEC V experts that explained how the computer advances the timing more under part throttle when the air meter is calibrated for larger injectors, because it interprets the smaller voltage signal from the MAF as the engine being under a lighter load than it actually is (the computer advances the timing during light load cruise). With big injectors like 36lb or more this can become a problem. To counter this problem they would reprogram the computer and tell it that the engine was SMALLER than it actually was. This would make the computer think the engine was under more load. (Same amount of air moving through a smaller engine means the engine is working harder.) This would also affect the air/fuel ratio, because the computer tries to match fuel delivery to the size of the engine. The point of all this is that if you are adjusting engine size with the Tweecer that may be what is screwing up your A/F ratio. Someone really good with the Tweecer needs to chime in here.

dcarlson · Jun 10, 2005

More air shouldn't make it run lean if the MAF is reading the increase in air. Could be the change in throttle position sensors or some other combination of factors.

jruppert · Jun 10, 2005

Originally, I installed an Accufab 80mm with a 90mm inlet. This proved to be too large. I loaded up the pro-m 24lb file for tweecer like I always have and its always worked. It would idle fine and even when you rev. The minute you put it in gear and let off the clutch it would run until you hit 1/2 throttle. Then it would cut out and run lean. WB would record lean also. I tried over and over to cure this and I wouldnt find a fix. Finally I loaded up a pro-m 30lb and it would run. So it ran fine then I decided to take the throttle off and sell it because it was just too large. I ordered a 75mm. In the mean time I drove with a stock 89 throttle and it ran reasonably well considering the small throttle size. Then I decided to take the pro-m off and send it back to get recalibrated for my 30's. At this point I had to use the stock mass air. I went to tweecer and loaded up the stock meter numbers. It ran surprisingly good and maintained a 13-14 on WB. I get the new throttle and install it. Bam.. I am back to running lean and never changed anything in the computer. So this is where I am at now. I think I may just park it til I get the meter back.

jrichker · Jun 11, 2005

TPS problems? The TPS seems to be the thing that changed when you swapped TBs.

BaXTeR3221 · Jun 11, 2005

If your using the tweecer, you need to adjust the MAF transfer along with the injector slopes and breakpoint. Only changing one piece is going to cause headaches.

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