Engine Backfiring and Unable to Diagnose.

[Goeman]

I've got a huge pain in the backside problem with the car that has mystified all comers. Basically the engine revs normally until 5+k rpm and there it will backfire, pop and bang like mad and will not rev any higher. It does this in all gears and out of gear. Engine hot or cold. It pulls cleanly and strongly up to the point where it backfires and then it's like hitting a brick wall. The engine is standard with the exception of the exhaust system which is a Che type manifold, type approved cat (new, I replaced the old knackered one in the hope it'd fix the problem) and a blue flame back box.

There is no CEL light and no error codes logged at all. Both I and Toyota have confirmed this. I've tried a new MAF, new spark plugs and coil packs with no improvement. The car didn't have a battery for 3 weeks so the ECU should have been reset but that didn't help. The car drives normally below 5k rpm and there is fuel popping in the manifold when it backfires so the fuel pump works. Toyota did two hours of real time diagnostics and sent it off to Toyota's UK head office and they came up empty handed except for a vague suggestion of putting the original manifold back on (the car ran fine for a year with the aftermarket manifold).  

So here I am completely stumped. It's been months now, in fact the car hasn't moved in two months because I got fed up. I've pretty much stopped using this forum because I haven't been using the car which is a pity. I have done a search by the way on both the forum and google. While I have found 1 mention to this problem the was never and diagnosis or solution. I PM'd the person that had the problem but have had no reply.

I'm left to think that the ECU is goosed in some way. Am I right in thinking that if I replace the ECU I will have a problem with keys? Would I be better of just skipping to a piggy back ECU and map away the problem?

Anyone have any ideas? Anyone know of anywhere that can help me where Toyota have failed? I located in the north east but at this point I'm very much willing to travel.

I really hope someone can help. I need to get back to doing trackdays.

Thanks in advance.

[Cap]

Do a Compression Check..  start from there..  

Post the Results..  

I'm thinking something with Valves..  Like a Cam out of Time..  or the VVTI going Wacky..  

Try pulling the OCV plug on the Head..  so the VVTi has been Turned off..  Try it..  see what happens..  

The With the OCV plug Pulled..  Pul the Cam Position Sensor..  ( Tranny side of the head..  pointing toward the Firewall ) and then Start it and run it..  

By pulling the Cam Pos Sensor..  the Ignition will be forced to Fire Two Plugs at Once..  and the ECU will will use a Different Fueling Scheme..  

Try these things..  and report Back..  

Cap

[Goeman]

A good, quick reply. I'm away from the car until the end of next week (I'm on an oil rig) so these test will have to wait until then.

I thought about the VVTI just not working but I would have thought that the engine would still rev without it. I don't know though. I'm a hammers and spanners type of home mechanic. Electrical stuff is like witchcraft to me.

[Cap]

Nother Thought..  

Knock Sensor..  It might be pulling timing because of something it's hearing in the Motor..

I don't have a Fix for that..  other than Changing the Knock Sensor..  Not Fun..  

Anybody know what happens if you plug a NEW Knock Sensor into the Harness..  but not mount it to the Engine..  will It Still think all is OK..  or will the ECU get Mad because It can't here any engine Noise?..  

Cap

[Anonymous]

Must admit I'm not the best at this type of diagnosis but could it be something simple like an injector? If so I have some in the for sale section that could be used to test.

[Anonymous]

injector poss. it might not have a good spray pattern on it so not getting enough time at high rpm to produce a decent flame wall. vvti not going to be as it is only doing something at the bottom rpm to reduce emissions. also might be worth a try to take off and clean up the crank and cam position sensors might be getting a miss read as they might be a bit dirty. knock sensor if it was to pull it would put less fuel. to me it sounds like the fuel is deffinatly there just not burning right. i know its a travel but i do have loads of engine parts if you ever want to pop down and just swap parts over to see if there was any difference.

[markiii]

injector poss. it might not have a good spray pattern on it so not getting enough time at high rpm to produce a decent flame wall. vvti not going to be as it is only doing something at the bottom rpm to reduce emissions..

vvti is operationall through teh rev range

[Wabbitkilla]

All useful stuff here, I'd be looking at sensors and their wiring about now.
Cam position, Crank position, knock.
vvti operating or not operating would not cause this, I know from experience about that much.

I simple test of the ecu would be to swap in an Apexi PFC for a test run, default map would be enough to run the engine smoothly and it negates any bother with the immobiliser and keys. I wonder if an MR-S ECU would be useful for that too?

TBH though the ECU's in these cars are pretty robust ... I doubt that is the cause.

[markiii]

also look at the fuel pump, if it can't provide enough pressure  or flow for the higher rev range a similar result might occur

[Cap]

Goeman:

While you are doing the Compression Test..  Pop the Cam Cover off and run the Valve Clearance..  and while you are in there..  Do a Gross Check of Spring Tension of Each Valve..  By wedging a Screwdriver ( or the Like) Between the Cam and the Lifter Body..  

The Clue here is at happens at 5K RPM loaded or Not.. so a Broken Valve Spring Might be at Play..  

Cap

[Goeman]

Thanks for the replies. I'll get on to these things when I get home.

Just a few things to add. This is a fault that just happened one day and not a gradual thing. The car was fine. I went to work for two weeks came back and started using the car. I didn't know anything was wrong when driving around town but then discovered it when I got to a 60mph road.

I think the fuel pump and injectors are working because of the un-burnt fuel because of the fuel poping in the manifold. As it was my only car (I've since bought an Accord Type R) I was driving around in it a lot and did a few long journeys. I doing think that with a lot of fault find and testing, the un-burnt fuel finished of the old cat which meant I had to get a new one.

It also needs to be noted that Toyota recorded lots of real time data. I assumed/hoped this would include readings from all the sensors and I would assumed/hoped that when this data was analysed that they would check that all the sensor readings were within spec.

Saying all that I am willing to try things and spend money on the problem. I just want my track car back.

[andywood]

I know that you mention trying new coil packs, but did you use fresh coil packs for all four plugs??

Have seen problems before with coil packs shorting at high rpm/energy and it being very hard to trace from engine characteristics.
Thought worth double checking as clear that fuel supply is good but lack of ignition.

Andy.

[Goeman]

I bought 1 brand new coil pack and tried it in each cylinder in turn. I then bought new spark plugs and did the same again. I tried and brand new MAF as well.

[Dyn-Evo]

Sounds coil-pack / injector related to me, assuming all the other things you have checked are ok....

My missus had a Puma which did almost exactly the same: do you get loads of blue smoke out of the exhaust when it does it?

Problem with that was the ECU had condensation in it which shorted the injector transistors out.....
Bugger to diagnose.....  s:roll: :roll: s:roll:  

Anyway, I would suggest replacing ALL the coilpacks with new ones...but first, I have a spare 1ZZ ECU you could try, if you wish....?

It could also be a dirty / worn / loose connector to either the injectors or coilpacks (1ZZ is COP, isn't it?).
Check ALL the plugs / connections / loom BEFORE lashing out dosh on new bits: I've been down this road many times, and you just end up out of pocket, with a load of spares you'll never really need....!  s:D s:D  

...and the REAL problem when you find it ,turns out to be fixable for free, the majority of the time...  s:lol: :lol: s:lol:  

If you want the ECU drop me a line...?

[ChrisGB]

Only thing that springs to mind is the crank position sensor or the connection to it.

Chris

[Anonymous]

Only thing that springs to mind is the crank position sensor or the connection to it.

Chris

+1

[MattPerformance]

Could you describe the characteristic as being similar to hitting the rev limiter?

[Goeman]

Hitting the rev limiter is a lot smoother and softer. With this the revs jump around by about 300rpm and like I said before, lots of popping and banging from the exhaust. It's not always in the same place but always between 5-6k rpm.

Dyn-Evo. I know I said I'm willing to spend money but I think buying 3 more on the off chance is excessive. I have 1 new coil pack which I have tried in all the cylinders. I would have bought another ECU to try by now but I believe there are issues with keys. I'm still not completely clear on that though.

I will try taking off, cleaning, reconnecting, etc. all these sensors but wont they have thrown up a CEL light or been noted in Toyota diagnostics if they were not connected or faulty?

What do people think of Toyota's notion that the aftermarket exhaust manifold was is blame? They reason they gave was iffy at best (something about it might complete a circuit) but like I said before the manifold was on for a year with no problems.

[Goeman]

I forgot to answer one question. There is no smoke of any kind. Blue, white or whatever.

[Dyn-Evo]

I forgot to answer one question. There is no smoke of any kind. Blue, white or whatever.

Well, that kinda rules out ignition / fuelling, then..?

So, as mentioned before, could be crank / cam timing sensor-related....?

I did suggest swapping out all 4 coilpacks...but I also advised checking the connections, etc, BEFORE spending any money....?  s:wink: :wink: s:wink:  

Does make you wonder if the Toyota mechs are actually clueless...? After all, they are meant to have the best diagnostic gear for Toyotas....and they come up with a basically useless conclusion...!?   s:roll: :roll: s:roll:  

Maybe your knock sensor has worked its way loose? Mechanically, not the electrical connection.....just a thought..?   s:? :? s:?
That would probably cause a similar effect..?

[Goeman]

The connectors for the coil packs are fine. They're like new. The whole engine bay is in pretty good condition. The car had a pretty easy and well cared for life until I got my hands on it and used it properly.

[krazysteve]

I had a similar thing on a MX3 V6, (track day project) i went down similar paths as you, removed fuel pump to find crap in the tank and fuel filter part blocked.
Repaced the filter and cleaned the tank, now rev's as it should.  s:bounce: :bounce: s:bounce:

You do say that it has driven like it was meant to be?
maybe it has picked up some crap in out the bottom of the tank??

[Dyn-Evo]

Hmm..!
Given that there is a LACK of smoke when this occurs, it does seem to point to fuel starvation rather than overfuelling / lack of spark...?

Fuel pump / filter would seem a logical starting point.....
You could attach a fuel pressure gauge to your rail and check things out: I had one fitted to my MK1 s/c dashboard, and it was very useful for monitoring fuel delivery on boost, etc.....  s:D s:D  

Mind you, if the ECU is getting signals from the knock sensor that it doesn't like, then it would retard timing and cut fuel accordingly, so you wouldn't get any smoke, etc...?

[ChrisGB]

Figuring it out....

It is not load dependent (won't rev past 5 or 6K RPM) regardless of engine load) which most probably eliminates:

Fuel pump / Filter / Pick up (fuel volume would be low at no load situation even at high revs)

Single cylinder misfire (even with one or two cylinders completely dead it would rev to limiter with no load on)

MAF (unless completely fooked, it would only be seeing small air volume at low loads)

Oxygen sensors (open loop operation at high revs high load)

Injector fault (dribbly one would not prevent running high revs and would cause low speed running problem, failed closed one would not prevent revving out on low or zero load)

Blocked inlet or exhaust (would rev out under zero load or not get to 5 or 6K under load)

Leaking inlet or exhaust (would still rev out under zero load, even if rough)

Compression failure (would still rev out at zero load)

Failing valve spring (would still rev out at zero load, would probably have dropped valve or clouted one by now)

VVTi system would throw a code, but even if failed with maximum overlap, engine would rev out under zero load

Mis fire is engine speed related but not load dependent which points to electrical issue:

Knock sensor unlikely to be an issue as it should only retard timing, so should rev out under zero load.

Something rattling in the engine or exhaust system could affect knock reading and cause the engine to pull timing, but then ECU would be running very retarded across rev range, so severe loss of performance and still should rev out under zero load.

Earth fault is a possibility, but odd if it only affected high speed running. Increased energy in the ignition system at high revs could be an issue if an earth point has developed a corrosion layer.

Crank position sensor fault. Inductive sensors tend to have bigger problems at lower speeds, but could be the issue, leading to mis timed sparks.

Alternator. Increasing revs would lead to increasing frequency of electrical noise / voltage spikes on the alternator output if a diode is on it's way out. Could cause confusion for the ECU as it would put spikes onto the power circuits and confuse signals from the crank position sensor or general ECU operation.

Flaky ECU, but odd it would work well at low / mid RPM range.

Defective rev counter, is it reading right or are you just running into the limiter and not knowing it?

Worth getting in there and tightening / cleaning the under bonnet earth points.

It is all I can think of at the moment. Gives me a break from work  s:D s:D  Don't think of trying to piggyback map around the problem, something is obviously not working right and a piggyback can only alter your fuelling and timing a few % away from the stock ECU parameters.

Hope it is sorted soon.

Chris

[mrzwei]

This really does sound like a cam timing related issue. It's the opposite of what you would get if you fitted a hot cam to a non vvc engine ie popping spluttering and backfiring until the revs built up and the engine was 'on cam'. Your engine seems to be doing the reverse and  going 'off cam' at 5000 revs.

I think that I would try to positively eliminate the vvc mechanism as a possible cause before moving on. The fact that there is no cel is not necessarily sufficient (I've got codes which included a cam sensor and co2 sensor which are not throwing a cel).

So how can you test the vvc would be my first question.