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3.9 EFI miss fire


Deer hunter
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I wonder if any of you boffins out there could help an amature that has run out of skill, trying to sort 3.9I that is missfiring.

Car has been standing for 2 years in a garage.

Would not start, when it was put away, already had new HT leads, dist cap, plugs and coil.

Thought I was clever when I diagnosed rotar arm shorting to earth and off it started.

Smoke and S**T everywhere.Stinks of petrol fumes.

Will not tick over, is missing and is obviously over fueling.All the plugs are black and stink of petrol.

I have carried out the test on the airflow sensor as per manul and is Ok.

ECU was swopped for a known good PRC9611 14CUX,mine is PRC7067 14CUX, I am told this should be compatible, did not cure the problem.

I think the air byepass valve is stock due to standing so long, but I am told that will only affect tickover and not higher revs. eplacing this valve soon.

Other sympton is strange loud whooing noise coming from the air filter.

The noise is still there, if I disconect pipe from airflow metre to plenum chamber .(obviosly engine stops) but in that short period, noise is still there.

I have found a guy who rents out diagnostic tool, that plug into the socket next to the ECU.

The pins on the diagnostivce tool are round, the only empty socket I can find next to the ECU is black, but has flat pins.

There is a white plug and socket, that looks like it is just a link connection.

Any help would be very much appreciated.

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I trust the petrol is not what was in the tank when it was put away? If it is I'm slightly surprised it will even try to run as the petrol will have deteriorated - and will cause huge clouds of smoke. Drain and replace with new fuel.

If the replacemant dizzy cap and rotor arm are not genuine parts then you are wasting your time doing anything else. The V8 does not like pattern parts & there is a poster on another forum who admits to spending around £600 replacing bits on a RRC when the problem was the pattern rotor arm.

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If it's been stood for two years then cranked for ages before coming to life there could be all sorts, first off:

- Plugs are probably coated in s*** now, change them for proper NGK ones.

- If the leads were new 2 years ago, change them.

- If there are any non-genuine ignition bits, change them.

- If the fuel is 2 years old, empty it and run either normal fuel & lots of redex or some BP Ultimate through it to try to un-gunk it.

- If it's over-fuelling it's either airflow meter or coolant temp sensor, since you say the AFM is working I'd spend a fiver on a new coolant sensor.

THEN if it's still unhappy we can delve into "normal" diagnostics. FWIW I doubt renting a diagnostic doodah is going to help much, the 14CU system is not exactly a supercomputer and it's just as easy to diagnose "by hand".

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Dead rat/bird etc in the air filter?

Just to balance some of the (very sensible) advice given above - my 3.9 EFI stood for 2 years on the drive and fired up on the 3rd ten-second crank and stopped smoking after 30 secs or so - with old fuel and most of the ignition system old, pattern and ****ty.... (although it did miss on one pot for a while but I put that down to a stubborn tappet) :unsure: If fact it was that V8 roar that convinced me not to scrap it :)

TwoSheds

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Dead rat/bird etc in the air filter?

Just to balance some of the (very sensible) advice given above - my 3.9 EFI stood for 2 years on the drive and fired up on the 3rd ten-second crank and stopped smoking after 30 secs or so - with old fuel and most of the ignition system old, pattern and ****ty.... (although it did miss on one pot for a while but I put that down to a stubborn tappet) :unsure: If fact it was that V8 roar that convinced me not to scrap it :)

TwoSheds

No, not rat or bird, I wish it was.

The story so far, changed air flow meter working fine, airbypass valve new, fuel temp senor and coolant sensor , new, plugs,leads,distrib cap,rotar arm.

Now discovered that the sump if almost full of petrol and oil!

Drained out aload.

Worked out by removing the fuel temp senor, there was no pressure, therefore all the fuel is going straight through the injector and past the pistons.

Have a full rail and injectors on the way, used.

So took off the cover, to prepare to fit replacement injectors, removed ram housing to discover that everthing is covered in oil/petrol except one inlet??

Does imply head gasket ?

I wish I had never started .

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I didn't think the drilling for the fuel temperature sensor went all the way into the fuel rail, I thought it was a "dry" fitting (it is on mine). A good way to check what's going on is to fit a clear inline filter in the return from the PRV - this will show you if there is a flow or not.

The plenum is usually a bit grimy, the crank case vent blows oil vapour into it, whatever doesn't get sucked in and burnt will stick to the inside. If your sump is full of petrol and oil, then the plenum probably will be too.

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Sounds as tho you may have an injector or 2 not closing, this way the fuel keeps on coming into the engine and the pressure drops sometimes enough to make it misfire but has enough to run.

Would suggest you do a fuel pressure check both with and without the engine running, should be 28ish minimum up to around 34 ish if lucky it will drop a bit from whatever the setting but not much when it starts.

Then maybe get the injectors ultrasonically cleaned tested, or shiove in a know good sh set.

Visual inspection won't show much

Nige

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The fuel temp sensor only measures the temperature of the fuel rail steel pipe, the sensor does not come into contact with the fuel.

If could be that the fuel regulator has jammed, or, that there is no vacuum to the reg on tickover.

However, for vast amounts on fuel in the oil, then you are looking at permanently open injectors …………. If you have a wiring fault where any one injector on either bank has a short to earth, then all the injectors on that bank will permanently open ………. When that happens it stinks of fuel and usually misfires on all four of those cylinders………. And the oil level will rise by a litre or two of petrol.

:)

Ian

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Sounds as tho you may have an injector or 2 not closing, this way the fuel keeps on coming into the engine and the pressure drops sometimes enough to make it misfire but has enough to run.

Would suggest you do a fuel pressure check both with and without the engine running, should be 28ish minimum up to around 34 ish if lucky it will drop a bit from whatever the setting but not much when it starts.

Then maybe get the injectors ultrasonically cleaned tested, or shiove in a know good sh set.

Visual inspection won't show much

Nige

Thanks for that

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