Anyone know anything about Jap cars?

[mcbonio]

I know this is an E30 forum, but you all are such a knowledgeable bunch you just might know...

My brother has a '94 Toyota Supra, JAZ80 engine, non turbo. 3L - 24v twin cam.

We changed the spark plugs, ignition leads, dizzy cap and rotor arm as routine maintenance, the car worked great for a day then began to misfire at high revs. So we thought maybe there was a faulty component and put all the old stuff back in one by one to try and isolate the problem. No luck. The car idles fine and drives fine, until you push it past 4k revs it then begins to splutter and misfire.

I've checked everything and just can't figure out what the problem is.! Damn jap cars, E30s are so easy to work on.

Theres a prize for the winner.!

-Mcb

[Speedtouch]

Try a compression check, and check the engine earth strap. May be worth disconnecting the ECU/battery, leave it for a while to reset it, then leave it to idle for at least 10 minutes to enable base idle settings to be learnt, then switch off, then take it for a drive throughout the rev range.

Other causes of misfiring may be a dodgy batch of fuel, or cambelt has jumped a tooth.

[mcbonio]

Cheers speedtouch,
Its a strange one, it was working great when we changed all the ignition stuff then started misfiring at 4k revs. So we put all the old stuff back in and it was fine for a day, then started misfiring again at 4k revs.

We suspected the 4pin plug which connects to the dizzy housing as being faulty. The timing is electronically controlled I believe. Would a faulty dizzy electrical plug cause these problems?

[Aero1]

Not being funny mate but are you sure you have the plug leads going to the right places?
I had exactly the same problem on a car I was working on and it turned out to be that two leads were swapped over by my own carelessness, it looked right but the problem only came out at higher revs. Lots of head scratching and then someone suggested that the leads were wrong and bingo. Easy fix

[E30BeemerLad]

I would say the coil packs that sit on top of the plugs may be cracked. Inspect them for cracking

[Speedtouch]

We suspected the 4pin plug which connects to the dizzy housing as being faulty. The timing is electronically controlled I believe. Would a faulty dizzy electrical plug cause these problems?

A faulty connector to/from the dizzy will almost certainly cause issues! Try spraying it with some electrical contact cleaner if it shows any signs of corrosion.

[E30BeemerLad]

This is a mk4 supra right?
if so it has the 2jz ge engine. To my knowledge (limited) there are no dizzy present,so I'm baffled how you have changed the cap and leads

[tomislav]

Is it the pop up headlight supra or the rounded shape supra?

Had issues with my pop up headlight shape one (mk3) and it was an HT lead, found that out by taking 20000 volts up my arm briefly from lead 3, not advised but it isolated the problem!

[mcbonio]

Hey E30beemerlad, You would normally of been right, but his car has a TRD tuned JZA80 naturally aspirated engine, Its had an engine swap at some point in its life, it was only imported in 2009, no service history! So yeah dizzy cap and rotor arm present...

It has brand new HT leads, I'll double check the firing order and check to see if the cables are mixed up. Can't hurt to check.

Cheers guys.

[Speedtouch]

Use a digital multimeter to measure the resistance of the HT leads. They should all be approximately even, at around 5-6 kilohms (5,000-6,000 ohms) or so, apart from the main HT lead from the distributor centre kingpin, which being either shorter or longer will be proportionally different from the spark plug leads.

[mcbonio]

Cheers speedtouch, will do that tomorrow.! Good input.

[mcbonio]

Ok big thanks to Aero1..!

It was indeed the HT leads, 2 had become mixed up. We stripped it down and started again. All working fine now, another headache solved.!

Thanks buddy.!

-Mcb

[Aero1]

Glad I could help out mate.
Quick fix, everyone's a winner.

[Aero1]

Theres a prize for the winner.!

-Mcb

Didn't see that bit.

Brucey Bonus