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rincewind23

Dead MAF?

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Hi all,

I've got Defender 90 but it's got a 3.9v8 from a Discovery so I'm posting here..

I've had it for about three weeks - it's been running fine but then yesterday it started messing around - it wouldn't rev when I hit the accelerator. It was intermittent to start with but then went full on broken. I managed to limp home in 1st gear on idle.

Now when I start it up it runs lumpy for a few seconds before cutting out. If I disconnect the MAF it will idle fine, but then when I hit the accelerator nothing happens - well actually it threatens to stall until I let off the accelerator when it recovers.

I've hooked up rovergauge, and the throttle sensor is reading correctly - but the MAF reading stays at 0%. I piggy-backed on blue/green wire from the MAF and that reads about 0.5v when the ignition is on but the engine's not running, then goes up to about 2v when the engine is cranking.

Is my MAF dead? Or is the ECU just not reading it for some reason?

Cheers,

Kev.

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It appears the MAF is reading correctly - I managed to get it to idle earlier (at about 400rpm - constantly threatening to stall but managed to lurch along) and on rovergauge the MAF (direct) was reading bouncing around 30-40%. I still have the issue where it stalls if I touch the throttle.

Without the MAF connected, it idles better and if I slowly apply throttle I can get the revs to rise consistently; if I stab the throttle, it will die (or nearly die).

Could this be a fuel pump issue? It runs but when I disconnect the return pipe it just seems to be gently pouring out. I would expect gushing since it's supposed to be pressurised, but that's just me guessing.

I have ordered a fuel pressure gauge kit, since there is a schrader valve on the fuel rail. So I should hopefully be able to check pressure tomorrow.

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Well, it's not the fuel pressure - the gauge arrived at lunchtime, so I hooked it up (had to hook it in-line next to the pump, since the schrader adapter is the wrong size for the valve on the fuel rail) - on the startup pulse it goes up to 35psi then during idle sits at around 28. From what I've read this is about right.

Does anyone have any other ideas? I'm really stuck now

Cheers,

Kev.

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Coil?

Dizzy?

Coolant temp sender?

What do the plugs look like?

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Coil and dizzy look fine - I think this is backed up by the fact that it idles pretty well when the MAF is disconnected (although this is more a guess than anything else).

Coolant temp looks about right according to rovergauge.

When I pulled the plugs they were covered in soot - probably from when it was idling lumpy when the MAF was hooked up. I cleaned them up but no change.

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AIUI, if you disconnect the MAF the ECU will use default readings so the fact yours doesn't run with it disconnected suggests something else is causing the problem.

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hey IanS,

Thanks for the reply. I think you might have misread my original post.. the engine runs *better* with the MAF disconnected, but still won't rev correctly when the throttle is applied normally (versus applying it extremely slowly, when the revs will pick up).

Cheers,

Kev.

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Yes, that's why I'm suggesting there's another fault.

Mind you I've only just noticed yours is a V8 so I'm probably wrong anyway.....

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I just sent it to a mechanic and after testing all the electrics, he says he put a clamp on the fuel return line to keep the pressure up and it runs fine. So I guess it's the fuel pressure regulator.. strange since I swapped it out for a known good one (off my kit car's rover v8).

Maybe a vacuum issue to the regulator? Anyway, going to collect it and do some more investigation.

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Iam having a very similar issue. I have a 94 3.9 and a week ago i put a new head gasket in and every other gasket on the way while cleaning things up. Since getting it all back together i can't get it to idle without it missing and blowing black smoke. It has new plugs, leads ,coil,stepper motor. I cant seem to get it to idle properly or drive and its doing my head in

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