TJ VRX misfiring at low revs

[maxtjvrx]

Hi,
Im new here ( name's Max) and saw a need to join up as my wife has had her TJ VRX for the past 17 years which she loves ( clicked over 270 K last week). It's been my responsibilty to look after / baby / service / repair it all these years which I do with pleasure as you all know they are a great car and even today I think they hold their own - genuinely a pleasure to drive.

Anyway enough of the Banter. Recently it has developed a pronounced misfire at low revs under accelaration which seems to peter out up the rev range but still is holding back on its usual sweet linear power band. No issues on starting or idling. Last year I replaced the fuel pump. Recently ( last week ) changed the fuel & air filters with the usual 5K oil and filter change - still misfiring but she says less so. So im thinking maybe 3 areas:

1. injectors ( get them cleaned)
2. plugs ( both banks) / leads / coil / distributor
3. Vacuum line

She says that the engine light did come on a few months back but only made a brief appearance and has not come on since.

My plan of attack is to:

1. lift off the intake plenum & clean the injectors ( need to replace the rocker cover gasket underneath it)
2. at the same time replace both spark plug banks ( due anyway)
3. replace the leads / distributor cap / rotor

Another issue is that it has started burning oil ( 0.5 litre per 5000 k's) which leads me to believe valve stem seals . Im thinking maybe a reason for misfire?? ( fouling plugs or other complications leading to misfire)

So im also thinking at same time while everything is off to replace the valve stem seals - thoughts??

Any help / advice / pointers appreciated.

Ciao.

[mcs_xi]

First thing I would do is unplug the Oxygen Sensor ( look in the passenger footwell and remove the vertical metal panel behind the carpet closest to the centre of the dash. Find a flat plug with 4 wires and simply unplug it.

This will force the ECU into a default map and it is a good check to see if the O2 sensor is defective.

take it for a drive and see if it is cured.

Second, the AFM could do with a clean or replacement, Third, Leads and plugs.

That is the order I would check everything.

[maxtjvrx]

Thanks - will do.

Hope its that simple.

[leadfoot6]

Not that I have experienced this problem myself, but I have read here at AMC that such symptoms MAY be an indication of a failing coil in the distributor.

The only sensor or engine related problem that I have had was a failed Air Flow Meter which I cured in March last year with a second hand one @ 175,000km traveled.

It had been stalling at idle/low revs, becoming more frequent, but no misfire as such.

Your symptoms do not replicate those that I experienced, hence my suggestion of the coil.

[cooperplace]

when you're replacing plugs, they're a lot cheaper from Rockauto, if you can wait for them to come from the US.; likewise rotor and cap.

[rumpfy]

From your observations I would have said 'distributor'. Then I saw 'Leadfoots' post. I have experienced the problem and replacing the distributor fixed the problem.
I considered to replace the coil only ($175) but not having seen the distributor before, I opted to replace the whole unit ($350). Some members have found the distributor cover was the problem, so to replace both coil and cover made the economics barely worthwhile.
If you do take the distributor out, make absolutely sure you know where the reference position for the rotor button is. Getting to one of the bolts is a p---k of a job, but do-able.

[WytWun]

OP,

First thing I would do is unplug the Oxygen Sensor ( look in the passenger footwell and remove the vertical metal panel behind the carpet closest to the centre of the dash. Find a flat plug with 4 wires and simply unplug it.

This will force the ECU into a default map and it is a good check to see if the O2 sensor is defective.

This check is best done with an ECU reset (disconnect battery for at least 15 seconds) before driving to force clearance of learned fuel trims (which become skewed by a failing sensor). If the ECU is not reset, the poor learned fuel trims continue to be used even though the sensor is disconnected, which can result in the test not showing what it should. Be aware that this may result in poor idle in some cars.

Also note that no CEL will be visible with either a failed or disconnected oxygen sensor in these cars.

[maxtjvrx]

I will do the coil. Any advice on cap / rotor as mitsu dont sell them anymore? .

Repco quoted a fuel miser cap and rotor- Thoughts?

[leadfoot6]

Possibly you are best to obtain these from forum sponsor Mits-Fix in Melbourne.

I have purchased a number of items from him.....all good.

He has complete, brand new, non-genuine distributors for $335.00($318.25 after ebay discount) including standard postage.

https://www.ebay.com.au/itm/Distribu...item2f0cc279cf

You can buy caps(aka covers) and rotors individually, but my money is on a failed coil, and I would replace the whole lot in one go.

I believe a unit supplied by Mits-Fix will also come with the correct size "O" - ring at the base of the distributor.

Most higher mileage 6g74 engines will have potential oil leak problems from the base of the distributor by this stage even if you have not removed and reinstalled the distributor due to failing "O" - rings.

Even if it is just initially a problem caused by failing cap or rotor, at some point in the future the coil and/or the "O" - ring will probably fail, especially after 270,000 km.

Just get it all in one go and minimise the headaches.

If you are on a tight budget he has complete second hand units for $90 incl. postage - 90 day warranty.

I imagine that your friendly local mechanic, if you have one, will not charge too much just to do a distributor R&R if you are worried at all about doing it yourself.

Whatever you decide to do, please keep all of us updated as to the eventual outcome.

Such feedback and knowledge is quite beneficial to all of us, but it is a procedure that sadly many new members do not follow.

[leadfoot6]

From your observations I would have said 'distributor'. Then I saw 'Leadfoots' post. I have experienced the problem and replacing the distributor fixed the problem.
I considered to replace the coil only ($175) but not having seen the distributor before, I opted to replace the whole unit ($350). Some members have found the distributor cover was the problem, so to replace both coil and cover made the economics barely worthwhile.
If you do take the distributor out, make absolutely sure you know where the reference position for the rotor button is. Getting to one of the bolts is a p---k of a job, but do-able.

When you experienced the problem related to in your post, was an "error code" generated?