Want some opinions on VR4 misfire issue - Brindabella Motor Sport Club

Marcus · 29-01-2007, 03:30 PM

Problem -

At an event near Christmas, the car began to develop less power. After a few more runs, a misfire began to develop, with the plugs showing up that the engine was possibly leaning out. The miss settled into a repeatable 4500 rpm misfire that steadily got lower into the rev band, at this point it shows up at 3500. Sounds a lot like the car is trying to use an antilag system. It still gets full boost even when misfiring but spool is slow and throttle response poor.

Ruled out -

Fuel system. I thought that this is what it was, pulled system apart and found a cracked filler pipe that had let water in to the system, a ****ed filter, dirt in the tank and suspiciously watery fuel, which did have some ethanol in it and as some would know, Ethanol is hygroscopic. A cracked fuel filler pipe would be perfect to let a load of water or condensation in. Tank came out, cleaned, fuel pump checked, any blocks removed. Miss now develops lower in revband.

Thinking it could be -

The car tends to run rich. It could be the spark is being blown out because the spark is too weak. Plugs were the wrong ones, but even with the right ones, the misfire is there. Spark Leads are tested and found to be within range.

So it appears I have insufficent spark. What's cuasing it I have no idea as yet - I do know there seems to be an earthing issue somewhere else and that needs to be checked. What else should I look at? What else could cause a misfire like I have?

Raynman · 29-01-2007, 03:51 PM

I was having a similar problem this morning with my road going liberty RS - but I thought it may be clogged injectors or bad fuel.

Turned out one of the wires off the module was not making good contact, or one of the plug leads was loose. Runs fine now.

Have you checked your wiring and that your module still works fine.

Also - how about the fuel regulator?

Mark · 29-01-2007, 04:22 PM

I've had something similar with the Evo. Taking more and more boost to get up hills? Makes good boost numbers but doesn't just go?

In my case it was the cam belt pulley chopping out as the big arse pulley bolt was loose and with a fugged thread. Partly my fault for not checking it every rally. Basically static timing was retarding as the keyway in the pulley got bigger and bigger as it chopped out.

Once you've identified you don't have an air leak somewhere, checking the ignition timing. If that looks okay, remove number one spark plug lead, jam a screw driver down there and check that the top of the piston travel co-incides exactly with the timing mark being right on, on the pulley.

Another reason why it's something to do with the ignition is:
-you're still getting full boost despite the misfiring. This says to me that the turbocharger is doing the job, and still pumping the same amount of air in the system.
-sounds like the car is using an anti-lag system: anti-lag systems work by either diverting air into the exhaust manifold (I think as per standard Evo 4,5,6) or by retarding the spark.

Of course, you've got to have faith in your fuel pump, spark plugs and injectors being clean as well but checking your base timing is just a 15 minute job at most.

I'm happy to compare notes via PM if you want.

Mark

Marcus · 29-01-2007, 10:25 PM

Quote:

Originally Posted by Mark

I've had something similar with the Evo. Taking more and more boost to get up hills? Makes good boost numbers but doesn't just go?

In my case it was the cam belt pulley chopping out as the big arse pulley bolt was loose and with a fugged thread. Partly my fault for not checking it every rally. Basically static timing was retarding as the keyway in the pulley got bigger and bigger as it chopped out.

Once you've identified you don't have an air leak somewhere, checking the ignition timing. If that looks okay, remove number one spark plug lead, jam a screw driver down there and check that the top of the piston travel co-incides exactly with the timing mark being right on, on the pulley.

Another reason why it's something to do with the ignition is:
-you're still getting full boost despite the misfiring. This says to me that the turbocharger is doing the job, and still pumping the same amount of air in the system.
-sounds like the car is using an anti-lag system: anti-lag systems work by either diverting air into the exhaust manifold (I think as per standard Evo 4,5,6) or by retarding the spark.

Of course, you've got to have faith in your fuel pump, spark plugs and injectors being clean as well but checking your base timing is just a 15 minute job at most.

I'm happy to compare notes via PM if you want.

Mark

I agree it's most likely ignition and from what I've found, as VR4's get older the problems I'm having aren't exactly uncommon.

BTW, did you have to replace the pulley to fix your issue? Sounds potentially nasty.

afifield · 30-01-2007, 07:16 AM

A couple of possibilities:
- Check all connectors to sensors etc. If they're old or haven't been done with the right tool, they can shake loose giving you dodgy/intermittent signals.
- Check fuel pressure. If the reg has weakened, you'll get a crappy spray pattern.
- Check compression. If you've got a sticky/bent/burnt valve, it's possible that you're shooting flames out the exhaust valves, but that should cause probs at all rev ranges.

If all else fails, give Ken @ Macquarie Rd Auto Repairs (Springwood) a call. He did all the work on Gnome's VR4, so he might have some ideas. He's also got the diagnostic equipment there and is rally friendly.

Griffo · 30-01-2007, 08:59 AM

How did you test the spark plug leads? If it was only a resistance check then a faulty lead won't always show up. Best way is to go to repco & buy a tool called a stress tester. Cost about $10-$20. It actually plugs into the lead, has its own earth clip & allows you to test the leads under actuall engine running conditions. They have a adjuster to allow you to adjust the air gap. Anything under 25-30 KV air gap on the tools scale in electronic ignition system is considered weak. You can really see any lead that is even remotely suspect. Leads may not be the problem but you would be suprised how many leads found that are not working to their capabilities using a stress tester.

Rallyray · 30-01-2007, 09:10 AM

Wouldn't be a bad idea to check the fuel pump while your at it...

Chuck a flow meter on the fuel line and see if that might be causing the problem...

Raynman · 30-01-2007, 12:07 PM

Wasn't actually checking the leads themselves - just making sure they were on tight (you would be suprised as they do get loose with the engine rocking)

But if it is timing due to loose front pulley - if they are anything like subarus then it could lead to a damaged crank keyway. Bad news as you need a new crank (or you could glue the timing cog on permanently)

smee · 30-01-2007, 12:26 PM

Have you looked at the coil.
The Mazda was cooking the standard ones regularly. Went through 4 of them.
Changed it for a good Bosch unit and have had no problems, When I can put an individual one on each cylinder $$$$'s I will..
This coil is now replaced yearly as a consumable item and a spare kept just in case..

Matt Sosi · 30-01-2007, 07:29 PM

When I was naving for Jon Parker in the Evo 3 at Nat Cap last year, we had the same issue as what you were expereincing. Car lost power just after starting SS1, and midway through, it started to misfire badly.

Smee is right in that you may want to check the coil as, when we looking at causes, found the coil was cooked. Put a new coil in, a VR4 one at that, and the car worked a treat afterwards.

Matt

heyehy · 02-02-2007, 02:29 PM

had a similiar problem with my peugeot (but no turbo). it was the air flow meter. once it got to 3.5k it would pop and fart and struggle and then over 5k it was ok again.

2nd hand one in, and she was apples.

Marcus · 02-02-2007, 03:55 PM

Quote:

Originally Posted by heyehy

had a similiar problem with my peugeot (but no turbo). it was the air flow meter. once it got to 3.5k it would pop and fart and struggle and then over 5k it was ok again.

2nd hand one in, and she was apples.

The AFM is definantly good. In fact so good, it appears it will be on someone else's car at Minidulla

lxb02 · 03-02-2007, 02:01 AM

I had a problem like that with an Audi 1.8T, does the computer have any codes that you can read.

Mine computer had misfire detection stuff, and basically told me which cylinder has the issue. traced it down to being a faulty ignition amplifier circuit, that played up with heat.