Thread: Maf and ECU problem

Im running a 20v engine, with p11 ve distributor, GTIR ecu with Daughter board, and a Nissan q45 Maf. Im using a modified P10 loom.

I've recently started having some faults.

It would appear that on start up, the ecu comes up fault code 12, Maf sensor fault. Have tried another Maf with no sucess. If we plug in a laptop to the consult, start the car, the fault code comes straight up, if we reset the ecu using the laptop, the fault goes away and doesnt come back.

The second fault, is during driving the ecu goes into limp mode, with the fans running full time, and the ecu on its internal limp mode maps, surprisingly it actually drives and idles "ok", given that its got way different Maf and injectors to the original ecu settings. This would indicate a Daughter board fault, where it is loosing communication with the ECU. Stopping and restarting the car makes it go away sometimes, and last time i drove it for 10 mins without the fault reapearing

At first we thought it was one fault, but now we think its 2, which was making the diagnostics of the problem impossible to logic thru.

Next things to try is rewiring the Maf with new wires from the ecu direct, even tho the p10 loom is unchanged apart from the Maf plug on the end. We have to do this to eliminate it as a problem. The next thing is to try a different daughter board, unfortunatly i dont have another the same, so we need to burn the tune onto another set of chips and fit a different brand of daughter board.

If you think you might have any input on these fault, please post up.

Cheers!

I would check the MAFS wires first, check all the connection points you have put in. Then go over everything with the volt-o-meter every now and then if you don't find it the first time. It sounds just like a loose wire somewhere

Well its gone from bad to worse.

I think my map switcher has popped something on the PLMS daughter board, we had a couple of different maps i was trying, but one of them was from a different base map, ands switching on the fly, which is normally ok, caused a misfire, then it started the limp mode problems. Ive got another brand of board in there now, and that one has not gone into limp so far.

I ran new wires direct from the ecu plug to the maf , and soldered the wires straight to the maf to take all other factors out, and it still came up code 12, we have tried 3 q45 mafs with no sucess. We put a p11ve maf on and the problem went away. But thats really odd, as my tuner has been running q45's on turbo cars for ages with no problems, so we started looking for other cures. The only real reason for running the q45 is its a large diameter, which fits the factory 20v intake same as the original maf.

So we were checking wiring, maf placement incase it was a turbulence issue at startup and idle, and the engine stopped dead. Ecu wouldnt turn on. Tried another ecu with the daughter board, it powers up and the consult laptop says no faults, but has no power in the 12v main power for the maf and injectors, or the main ecu relay.

Its stuck about 60km away at my mates place, so we will have to tow it back here and get it in the garage, and then start pulling the loom apart. There must be a major wiring issue in the loom somewhere in the engine bay, as when i was moving the maf around i pulled on the loom a bit when it stopped.

Arg. Not happy.

Went down to tow it home, had another go at it and found there was no power to the ecu relay, and there was no potential to earth. This power comes from the 25 amp fuse by the battery, which is fine, so there is a wire break somewhere. I jury rigged a wire to this circuit and it fired straight up, and also is now code 55.

The maf is fed off the ecu relay power too, so if this wire or connection was getting loose, thats why it was throwing fault codes.

Now ive just got to pull the whole loom out to find the fault, and repair all the bits ive butchered up trying to find the fault, and putting the temporary fix in to get it home.

Cheers to James and PaulH for the help.

Well heres the culprit to the whole affair, its the 25amp fuse from under the bonnet.

I checked this with a meter to make sure it had continuity, and also was supplying power ok, but with the engine running and prothane mounts, the vibration was enough to cause a fault, and then finally enough to stop supplying power all together.

Got another fuse in there, but the whole excersize has been at the expense of my engine bay loom, which is now out of the car and missing a lot of the outer insulation.

We learn from these things, in future the lesson is to actually remove the fuses and physically check them, not just eyeball.

^^ Ain't that the truth?

another lesson learned.... sometimes we obviate things or just wont do them cos we're lazy...