MAF Fault that isn't the MAF....

Fûcking site.... Arrrgh.. I'm going out to to fix cars.....

Thanks Mark, I've just opened to report so haven't had a chance to look yet...

However, the report: I found the following and am not sure why I have 3 grounds

5 wire MAF.

Wire 1= grey 5v+
Wire 2 = brown/pink 12v+
Wire 3 = thin red 12- (ground)
Wire 4 = thick red 0v either way
Wire 5 = blue /black 12v- (ground)

The above was carried out in freezing conditions with rain pishing down and the MAF plug disconnected, ign ON.

I switched OFF the ign, plugged the MAF plug back in and switched the ign back ON. I bared a tiny bit of wire 4 (because my digickal multi meter probes are no longer sharp as I've had this one for over 12yrs) and put the Neg probe to it (the + was on the battery terminal) and was immediately rewarded with a 12v signal which told me that wire 4 is also grounded

So 3 wires grounded tells me something is awry with the wiring.

I need to remove the inlet manifold (my favourite job of all time ) and start tracing the wiring.

But before I do all that, I wonder if it is perhaps an LPG issue after all. This misfire is small, but annoying. It can be overcome by giving the engine more throttle, but that uses more fuel. It also increases when running on LPG making it even more irritating to drive as the delay in pulling away is markedly increased and the misfire more pronounced. This tells me the misfire is fuel related in that it is running lean on both petrol and LPG and is no doubt a base map over ride.

Now I wonder if the regular LPG warning lamp is because of this low fuel issue or because of the apparent short circuit in the wires to the MAF? I suspect the former...

I need to figure out if it is just a nipped cable caught on some metal or is it a wiring fault to the LPG ECU. Again, I'm reluctant to think that because surely if that were the case, the car simply wouldn't run on LPG at all. But when on a long run, it behaves very well on either fuel until you slow down and go to pull away again.

So I am now in the ball park and wondered if anyone has anything to add as to where might it be nipped or shorting out (any previous MAF experiences)?

Thanks Mark, I've just opened to report so haven't had a chance to look yet...

However, the report: I found the following and am not sure why I have 3 grounds

5 wire MAF.

Wire 1= grey 5v+
Wire 2 = brown/pink 12v+
Wire 3 = thin red 12- (ground)
Wire 4 = thick red 0v either way
Wire 5 = blue /black 12v- (ground)

The above was carried out in freezing conditions with rain pishing down and the MAF plug disconnected, ign ON.

I switched OFF the ign, plugged the MAF plug back in and switched the ign back ON. I bared a tiny bit of wire 4 (because my digickal multi meter probes are no longer sharp as I've had this one for over 12yrs) and put the Neg probe to it (the + was on the battery terminal) and was immediately rewarded with a 12v signal which told me that wire 4 is also grounded

So 3 wires grounded tells me something is awry with the wiring.

I need to remove the inlet manifold (my favourite job of all time ) and start tracing the wiring.

But before I do all that, I wonder if it is perhaps an LPG issue after all. This misfire is small, but annoying. It can be overcome by giving the engine more throttle, but that uses more fuel. It also increases when running on LPG making it even more irritating to drive as the delay in pulling away is markedly increased and the misfire more pronounced. This tells me the misfire is fuel related in that it is running lean on both petrol and LPG and is no doubt a base map over ride.

Now I wonder if the regular LPG warning lamp is because of this low fuel issue or because of the apparent short circuit in the wires to the MAF? I suspect the former...

I need to figure out if it is just a nipped cable caught on some metal or is it a wiring fault to the LPG ECU. Again, I'm reluctant to think that because surely if that were the case, the car simply wouldn't run on LPG at all. But when on a long run, it behaves very well on either fuel until you slow down and go to pull away again.

So I am now in the ball park and wondered if anyone has anything to add as to where might it be nipped or shorting out (any previous MAF experiences)?

Henry_b said:

LPG needs a perfect ignition system, if there are any weaknesses in the system it will be more pronounced on LPG.

Coils?

Click to expand...

No EAS

Henry_b said:

LPG needs a perfect ignition system, if there are any weaknesses in the system it will be more pronounced on LPG.

Coils?

Click to expand...

No EAS

This evening, I decided to trace the MAF wiring back to the ECU, in case there was a short circuit somewhere... There were none!

However, after stripping the top end of the engine (inlet off to access wires), I find I have to stick it all back together again tomorrow



I had rare fun inspecting every millimetre of the MAF loom... but I found the issue (I think) that's been dogging me since I bought this car!



OK, not the best photo, but you can almost see in the 3rd slot along that the greeny grotty mess is not what should be showing.

The plug is showing clearly that it is a mess



So I'm pretty certain this MUST be my MAF issue, because I have found NO other issue within the loom

Doo said:

This evening, I decided to trace the MAF wiring back to the ECU, in case there was a short circuit somewhere... There were none!

However, after stripping the top end of the engine (inlet off to access wires), I find I have to stick it all back together again tomorrow

I had rare fun inspecting every millimetre of the MAF loom... but I found the issue (I think) that's been dogging me since I bought this car!

OK, not the best photo, but you can almost see in the 3rd slot along that the greeny grotty mess is not what should be showing.

The plug is showing clearly that it is a mess

So I'm pretty certain this MUST be my MAF issue, because I have found NO other issue within the loom

Click to expand...

Nice bit of investigating, inspector gadget.

Doo said:

This evening, I decided to trace the MAF wiring back to the ECU, in case there was a short circuit somewhere... There were none!

However, after stripping the top end of the engine (inlet off to access wires), I find I have to stick it all back together again tomorrow

I had rare fun inspecting every millimetre of the MAF loom... but I found the issue (I think) that's been dogging me since I bought this car!

OK, not the best photo, but you can almost see in the 3rd slot along that the greeny grotty mess is not what should be showing.

The plug is showing clearly that it is a mess

So I'm pretty certain this MUST be my MAF issue, because I have found NO other issue within the loom

Click to expand...

Next question, how do you stop the moisture getting in?!

Well that green mess will not help matters, but looks like you have found the culprit
i take it thats the main ecu connector that sits behind the battery.

Well done @Doo a good find.
A proper clean and polish and some sealing up and you will be misfire free one hopes.

What a mess, that will take a lot of effort to get really clean, for sure there will be tracking between contacts as it is.

Great find

I bought a set of dental picks ages ago for just that job to clean terminals and remove small O rings

ie, like these

Thank you for all the replies. Yes it's the main ECU, but it lives behind my cruise control module The box behind my battery is empty...

Anyhoo, the green is dry and has been for a while. But I suspect it is the culprit as everything else is fine. So today, I'll mostly be taping up a million feet of loom

I've opened up the case and while the pins are grotty, the insides are clean and dry. Although I did find what looked like dusty grot between two bits of solder, as if water had boiled dry... I'm hoping not. If I put her back together and get the same misfire, I imagine I'll need to get it fixed.

I cleaned the pins on the ECU with an emery board I got from her indoors. I'm still puzzling how to clean the open ends on the plug, but I'm hoping the paper clip will reach inside and I'll scrape as much crud as I can...

Doo said:

Thank you for all the replies. Yes it's the main ECU, but it lives behind my cruise control module The box behind my battery is empty...

Anyhoo, the green is dry and has been for a while. But I suspect it is the culprit as everything else is fine. So today, I'll mostly be taping up a million feet of loom

I've opened up the case and while the pins are grotty, the insides are clean and dry. Although I did find what looked like dusty grot between two bits of solder, as if water had boiled dry... I'm hoping not. If I put her back together and get the same misfire, I imagine I'll need to get it fixed.

I cleaned the pins on the ECU with an emery board I got from her indoors. I'm still puzzling how to clean the open ends on the plug, but I'm hoping the paper clip will reach inside and I'll scrape as much crud as I can...

Click to expand...

Can you cut an emery-board into (pin-socket sized) slivers and insert/remove and then wash out with electrical cleaner?

Doo said:

Thank you for all the replies. Yes it's the main ECU, but it lives behind my cruise control module The box behind my battery is empty...

Anyhoo, the green is dry and has been for a while. But I suspect it is the culprit as everything else is fine. So today, I'll mostly be taping up a million feet of loom

I've opened up the case and while the pins are grotty, the insides are clean and dry. Although I did find what looked like dusty grot between two bits of solder, as if water had boiled dry... I'm hoping not. If I put her back together and get the same misfire, I imagine I'll need to get it fixed.

I cleaned the pins on the ECU with an emery board I got from her indoors. I'm still puzzling how to clean the open ends on the plug, but I'm hoping the paper clip will reach inside and I'll scrape as much crud as I can...

Click to expand...

The green stuff on the plastic is copper sulphate which is a conductor so will cause short circuits between the pins. you need to get rid of every trace.

Seems the car didn't like being fixed!

Started up and immediately knew it wasn't happy. Normally fires up to around 900rpm then in no time settles to 750rpm.

However, it revved up to around 1200rpm then started hunting up and down then after around 15 seconds settled down to around 850rpm.

Tried to rev it but she almost stalls.

Disconnected the MAF and now she's hunting 450rpm to 825rpm.

So clearly the MAF is making contact now and she's gone to full enriched and it stinks. I think I'll have a problem getting her to the indy because she's pretty much undrivable

I can only assume I've either fixed it and this is her needing fuel trims reset or I've introduced leccy to the part of the ECU that didn't get any for so long it's gone bang.

I'm concerned about the gearbox fault that's also suddenly appeared. It goes off after she starts so can't be a major issue. I didn't disturb the temp sensor at the oil cooler not is the battery faulty.

Doo said:

Seems the car didn't like being fixed!

Started up and immediately knew it wasn't happy. Normally fires up to around 900rpm then in no time settles to 750rpm.

However, it revved up to around 1200rpm then started hunting up and down then after around 15 seconds settled down to around 850rpm.

Tried to rev it but she almost stalls.

Disconnected the MAF and now she's hunting 450rpm to 825rpm.

So clearly the MAF is making contact now and she's gone to full enriched and it stinks. I think I'll have a problem getting her to the indy because she's pretty much undrivable

I can only assume I've either fixed it and this is her needing fuel trims reset or I've introduced leccy to the part of the ECU that didn't get any for so long it's gone bang.

I'm concerned about the gearbox fault that's also suddenly appeared. It goes off after she starts so can't be a major issue. I didn't disturb the temp sensor at the oil cooler not is the battery faulty.

Click to expand...

Gearbox fault is often a sign of low battery volts and as it goes off after the engine starts that more or less confirms it.

Datatek said:

Gearbox fault is often a sign of low battery volts and as it goes off after the engine starts that more or less confirms it.

Click to expand...

That may be a possibility as I used the radio for ages as I was taking the car apart & I also used my portable compressor to lift the whole car (I don't like leaving it parked with no air in the suspension) which may have drained the battery a bit. But I've never experienced this in the past when I've had a low battery, just seems coincidental after I cleaned up the grot, the car runs like a bag of nails and now this...

Doo said:

Thank you for all the replies. Yes it's the main ECU, but it lives behind my cruise control module The box behind my battery is empty...

Anyhoo, the green is dry and has been for a while. But I suspect it is the culprit as everything else is fine. So today, I'll mostly be taping up a million feet of loom

I've opened up the case and while the pins are grotty, the insides are clean and dry. Although I did find what looked like dusty grot between two bits of solder, as if water had boiled dry... I'm hoping not. If I put her back together and get the same misfire, I imagine I'll need to get it fixed.

I cleaned the pins on the ECU with an emery board I got from her indoors. I'm still puzzling how to clean the open ends on the plug, but I'm hoping the paper clip will reach inside and I'll scrape as much crud as I can...

Click to expand...

You can get dinky little files for cleaning the pins. Also, check YouTube for cleaning electrical connectors. Think there's something with spirit vinegar and salt.

Grrrrrr said:

You can get dinky little files for cleaning the pins. Also, check YouTube for cleaning electrical connectors. Think there's something with spirit vinegar and salt.

Click to expand...

Vinegar and salt would certainly enhance the corrosion Isopropyl alcohol is good or Aeroclene 50.