AFM removal/IAT problem(car doesn't start)
 

The car is a 1991 Mazda MX-5 with Megasquirt PNP installed for some months and everything was working great.

The car was turbocharged(with a Begi-S kit)and the AFM was removed. The IAT sensor used is the GM unit DIYautotune supply. After the conversion I downloaded to the car the 90-93 without AFM .msq and tried to start it with no success. The starter works(I see the belt and pulleys move) but I see no spark and I can't hear the fuel pump working. I tried downloading the map again and again but nothing changed. I also had one of the plugs removed and added a spare spark plug to it and there was no spark. (With the Megatune open and the MSPNP connected when I turn the key I see the car going to 200-300 rpm and power going to injector and a random 'reset' or 'reset 4' appears in down right instead of 'connected')

Trying to diagnose the problem I connected back the stock AFM (without changing anything, not even the msq on my MS with the 90-93 with AFM)and the car started immediately with the first try. Also I could hear the fuel pump working from the start.

After that I checked again the IAT connection at the AFM plug and everything was according to the MSPNP manual but the car still didn't fire up.

***The car right now doesn't have an o2 sensor since the stock narrowband is removed and an LC1 will take it's place but that shouldn't be a problem since with the stock AFM in palce the car starts without a problem...Just in case that was the problem I reconnected the stock o2 and the car still wouldn't fire up***

I can't understand what is going on and why the AFM has anything to do with the fuel pump and the problem is that I have to get the car running since I have a race event to attend this Sunday.

Car should start fine without the IAT connected. Maybe the firmware burn was unsuccessful. Try reburning the firmware and make sure you d/c the coils/ignitor.

I haven't changed the firmware when the car was started for the first time...Just loaded the 90-93 no AFM map.

After many tries I disconnected the ignitor and loaded the new firmware(following the MSPNP manual). After that I loaded again the base map. Nothing changed. The car still doesn't fire up...

The strange thing is that when the AFM plug is put to the AFM the car starts immediately...

What about that fuel pump wire mod you have to do on the 1.6? I'm not well versed on 1.6/MS installs. Is that needed with the PNP or only the custom built versions?

Nothing mentioned in the MSPnP manual about fuel pump wiring mod. :confused:

was the ST_SIG fuse pulled?

you need to reflash your firmware as the scale of the GM is different than that of the OEM AIT sensor.

Not a wiring mod, just the pulling of the ST_SIGN fuse, as Brainey said. It is step #1 (in large, red type) in both the Quick Start Guide and the Full Manual.

This is only required on the MSPNP for '90-'93, not on the regular DIY MS nor on the PnP for '94+.

The reason for this is that on these cars, the fuel pump normally operates on a closure to ground through the AFM, and the ECU cannot control it directly. They figured out a clever way to back-feed power into a circuit that normally senses when the starter is turning, so the ECU can control the fuel pump. You need to pull this fuse to prevent the MS's fuel pump output from discharging through the starter, which will cause an overcurrent condition and likely damage the MSPNP daughterboard.

So, if you didn't pull this fuse before you installed the MSPnP, you may have damaged its fuel pump driver. If this is the case, then it obviously won't run without the AFM there to keep the fuel pump on.

If you don't pull the fuse. The car will start and work great on the afm.
The afm regulates the power to the fuel pump. But when you pull out the afm. The ms controls the power to the fuel pump.

But if you turned the key over once with the st fuse still in place. It blows a resistor inside the ms for the fuel pump activation.

I found this out the hard way.

Check to see if the st fuse is still in place. if so, you will have to send it out to be fixed or fix it yourself.

Or just run the afm for a while.
Good Luck.

or worse comes to worse you jump the fuel pump in the diagnostics connector.

ST Fuse removed before the install of my MSPnP and that happened before some months. My car run great and the MS working perfectly...Checked again and the place in the fusebox is empty.

New firmware installed with the ignitor off and the car fires up without problem with the AFM plugged so no plug, burn ignitor, fuel pump or burned MS issue.

Everything happened this weekend and the only electrical change was removing the AFM and downloading a 90-93 without AFM map to my MS.

I really can't undestand what is going on...I'm going to datalog the attempt to start the car for the guys at DIYAutotune but any suggestion for a possible solution or explanation to my problem would be greatly appreciated since time is a problem.

Does your laptop connect with your MS with the key on?
If so, do you get a temperature reading for IAT?

With the AFM connected now will the car start and run with the no AFM firmware?

"With the AFM connected now will the car start and run with the no AFM firmware?"

or will it start if you jumper the diagnostic connector running without afm map and no afm? I mean you could allways just wire a relay to run that circut off of the ignition switch untill the problem was diagnosed.

does anybody know which resistor it is so that one could check it? I would imagine a cheap multimeter would surely cost less than shipping from Greece no?

The first datalog(datalog200811010226.xls) is with the car as is. The MSPnP has the 90-93 without AFM msq and the IAT is connected. The car can't fire up(the fuel pump can't be heard working).

The only change in the second datalog(datalog200811010240afmplugged.xls) is plugging back the AFM(still with the 90-93 without AFM msq in the MSPnP). The car fires up immediately(and the fuel pump can be heard working from the start)

temporary solution, leave the AFM connected but not in the intake tract. wire the IAT sensor directly to the MSPNP.

temp/perm solution would be GND to FP jumped.

paperclip FTW!

Could you please explain that???Are GND and FP pins in the AFM plug???

Yes, but I think they're referring to the ones in the diagnostic box on the left shock tower.

If you want to do it at the AFM connector, click the link in my sig. There is a picture and description of which terminals at the AFM connector you jumper to run the fuel pump. This is how my car was set up when I ran an EMU without the AFM.

Thanks a lot for the help to everyone...

Is there any possibility of damaging my MSPnP if I jump the connectors to run the fuel pump?

Unfortunately the link in your sig isn't working and I can't really understand from the wiring diagram...

In the diagnostic box those 2 pins should be labeled(on the underside of the lid) just jump them with a paperclip.