New problem. Engine stumbles

[mhuk]

Well the ecu came back.

Waste of time for several reasons.

ECU company I sent it too decided after saying yes we can test then decided no they can't.

Came back and plugged back and everything was normal again. I went for a drive and no issues. Drove home and next day another drive and issue returns.

Changed the TPS and bingo it's sorted. I should say we had the multi meter across the TPS before and the range on the meter was changing so thought it was good. Also run the engine without the TPS connected and had the same issue.

Tested on the bench and same result. Picked up a spare TPS and now car runs.

Decided to cut the lid off the TPS and see it's burnt contacts or something.

The problem was water in the TPS.

The cause was my water injection and a bad O-ring on the TB/TPS.

WI has been moved post TB.

I must admit I should have picked this up before and only when opened was a small amount of water so explains why sometimes I thought for a moment it had no issues and then it would up and down the revs.

Massive thank you guys. Yeah I'm a massive dick!

[Laird Scooby]

Originally Posted by mhuk

Changed the TPS and bingo it's sorted. I should say we had the multi meter across the TPS before and the range on the meter was changing so thought it was good. Also run the engine without the TPS connected and had the same issue.

I wish you had said the range kept changing on the multimeter earlier! It shouldn't have done, the TPS is simply two switches, getting a variable resistance (as indicated by the meter changing ranges) indicates either a FUBAR multlmeter or a fault in the switch.

Still, water under the bridge now - as opposed to all over the TPS!

Is your WI system one that meters the water exactly or is it just a fogger system that cools the incoming air charge? If it's the latter you may have given yourself another problem in that it will feed excess water in on idle.

Time will tell on that one, i did post the other ECU testing place further up the thread after you said you had sent yours off. Hopefully you won't need it though!

[mhuk]

I think I got mixed up with mazda TPS on the mark 2. They are verible as I setup megasquirt before. No costs involved getting it back :-)

Injects at 7PSI+ only. Runs off a honeywell pressure switch.

[Laird Scooby]

Originally Posted by mhuk

I think I got mixed up with mazda TPS on the mark 2. They are verible as I setup megasquirt before. No costs involved getting it back :-)

Injects at 7PSI+ only. Runs off a honeywell pressure switch.

The Mazda TPS is a potentiometer so varies resistance with throttle position.

The TPS on the majority of 7/9xx is a simple pair of microswitches, one for idle, the other for WOT (Wide Open Throttle) so if water was shorting out the idle microswitch, it would certainly have given the symptoms/problems you had.

I think i'd try moving the injection point for your water to between the throttle body and turbo to give a longer period of time to cool the inlet charge to avoid a "too little, too late" scenario by trying to cool the charge in the inlet manifold. As long as the water pressure is above boost pressure it should get the water in at any point so the further back the bettr and preferably before the throttle butterfly so if the water solenoid leaks, it doesn't fill the inlet manifold up with water.

[TonyS9]

I win again

Dave, do all of them have the WOT switch, I know its not used on the Turbo, so didn't think it was there, however I havn't looked for it. Might be good for some cheap tuning mods, but I'd still need a chip to remove the annoying power limit.

[Laird Scooby]

Originally Posted by TonyS9

I win again

Dave, do all of them have the WOT switch, I know its not used on the Turbo, so didn't think it was there, however I havn't looked for it. Might be good for some cheap tuning mods, but I'd still need a chip to remove the annoying power limit.

Have a look at Pg14, #3/50, should answer both questions Tony.

http://www.myvolvolibrary.info/Tech_...ction-3-39.pdf

In short, yes it does but it doesn't appear to be connected to the ECU so arguably available for whatever mod you may be thinking of.
Perhaps used in conjunction with a pressure switch (so the circuit was only complete under WOT and x psi or more of boost) to operate a NOx fogger solenoid.

As for the TPS and you winning, we'd already suggested it (i don't think i did in all honesty because he said he'd already checked it) en masse but were assured it wasn't that by the OP as he had tested it.

Sadly that's where the fault lay and because he'd assumed it was a pot rather than two switches read the varying resistance on the idle switch as being correct.
As the ECU would expect a binary response from the idle switch, anything over a certain level of conductance could trigger the idle map.

One of those things!