Spark problem or fuel problem?

[bartsau]

Well it seems the wagon is well and truly jinxed at the moment. If it is not 1 thing its another...

So over the past month or 2 it has developed what feels like a little flat spot when accelerating. Sometimes when holding a constant throttle the speed drops off a little put your foot down to the floor and give it a second to clear itself out and accelerates no problems. Sometimes when it is really bad it is almost as if it is going to slow to a complete stop, then suddenly it will clear with a backfire and take off like there was never a problem...

I have tried a second set of leads to no avail (I do wish to get a decent set but am unable to find good ones at a half respectable price). If anyone can recommend some decent leads at a reasonable price please fire away as I want to change these anyway.

It has been getting much worse in the last week or 2. Today it was as if 2 leads were on the wrong way well idling then 2 minutes later would have a slight pickup in rpm of about 100-200 and idle like a dream...

Just after ideas if this could be an intake air temp sensor, TPS, MAF, Crank angle sensor, fuel regulator, injectors, or something else.

I fitted MSD coil packs to it back in April/may.
It has iridium plugs which are just on 12 months old.
Have tried 2 set of leads (standard) both with the same effect.
Also, had a walbro GS341 fuel pump fitted about 3 weeks ago. Was ok after for a week or so and then started getting a little worse...doesn't make a difference regardless of fuel level though so thinking not this.
And last was the exhaust which was fitted 2-3 weeks ago.

Just don't know where to begin with it really.and seriously over fixing something on it almost weekly...

[Maka]

So it backfired? There may be a clue there - have a suss of the link & see if it applies to you. Good luck!

http://istevision.org/precautionary-...gine-backfire/

cheers, Maka

[bartsau]

Yep. Kinda leaning towards a sensor or spark issue mor than a fuel supply issue...

Going to check all the leads are on right and swap the MAF now. Plus reload the standard tune again to see if that was an issue with it...

[bartsau]

Reloading the standard tune again and trying a different MAF made no difference at all :(

[Maka]

Even though you've got the quarterhorse, can you still run a scan tool over it? Are your spark plugs showing signs of lean running?

cheers, Maka

[roberts]

what happens when you fit the stock coil packs?

[bartsau]

Originally Posted by roberts

what happens when you fit the stock coil packs?

That will be tried tonight.

Originally Posted by Maka

Even though you've got the quarterhorse, can you still run a scan tool over it? Are your spark plugs showing signs of lean running?

cheers, Maka

Going to try and get a new set of leads from Eagle Auto Parts (Right near work).

Then tonight I will pull the plugs and inspect them. I will also try coil packs and hopefully a new set of leads as well.

If that all fails then I think I will be taking it down to my mechanic and get him to run a scan tool and see if they can find the problem...

[bartsau]

Well turns out the second v8 I have here also had iridium plugs so changed all the plugs and leads (got a new set of Top Gun leads today).

No where near as bad as it was before hand. The plugs that came out all looked really clean. Slight grey/brown tinge to them but not running silly rich/lean.

Still has a fairly noticeable flat spot occurring u der constant acceleration somewhere around the 3500-4000rpm mark. Also, sometimes just feels like the brakes are dragging...

Didn't get to the coil packs yet will try them tomorrow night. And fingers crossed otherwise it will be something even more time consuming/costly :(

[Addz08]

Blocked fuel filter maybe...

[bartsau]

Originally Posted by Addz08

Blocked fuel filter maybe...

Fuel filter was replaced about 4 weeks ago. When the walbro fuel oump whent in. Had been doing it before that though so thinking it is not that.

[Bushbasher]

Those Top Gun leads are crap. For my money, the best bang for buck leads I've found are Eagle leads. I was going to say fuel filter as well but if that's been replaced then how about blocked injectors or that little inline mesh filter at the end of the fuel rail, assuming the V8 system has the same sort of filters as the i6. Alternatively, what about your exhaust. A partially blocked cat or a broken baffle in a muffler that's floating around can intermittently create too much back pressure which can manifest itself as power loss like a lean out feeling.

[bartsau]

Originally Posted by Bushbasher

Those Top Gun leads are crap. For my money, the best bang for buck leads I've found are Eagle leads. I was going to say fuel filter as well but if that's been replaced then how about blocked injectors or that little inline mesh filter at the end of the fuel rail, assuming the V8 system has the same sort of filters as the i6. Alternatively, what about your exhaust. A partially blocked cat or a broken baffle in a muffler that's floating around can intermittently create too much back pressure which can manifest itself as power loss like a lean out feeling.

Mmm I have heard some people don't like the top gun leads...At the end of the day though I was hoping to get it back working better. Plus they were a dam lot cheaper than anything else I could have gotten my hands on yesterday.

Thinking I wouldn't mind getting the injectors cleaned although I also, have a second spare set in the second motor. This though I am trying to avoid having to do as it is a PITA.

Don't know the mesh filter you are talking about but will check on the 6cly tonight and see if there is something similar on the V8.

I had thought previously that it could be the exhaust but since this has been replaced about 3 weeks ago with a complete brand new system I would hope it is not this. But I can't say it won't be as stranger things have happened.

Will try the coil packs tonight and then start looking at fuel side of things.

Could it be something like a Crank angle sensor? Or TPS?

[mik]

The last time it was running good.......... what work was done it after that in order?
Something I have always done on my cars if a problem came up I would recheck over my own work(or someone elses) to make sure I or they havent buggered something up, sometimes it could b3 something as simple as a mechanic working has accidentally moved/knocked/broken/ or forgotten something, maybe left a vacuum line off or an earth off, recheck, double check down the list of possibles.......... good luck.

[bartsau]

Originally Posted by mik

The last time it was running good.......... what work was done it after that in order?
Something I have always done on my cars if a problem came up I would recheck over my own work(or someone elses) to make sure I or they havent buggered something up, sometimes it could b3 something as simple as a mechanic working has accidentally moved/knocked/broken/ or forgotten something, maybe left a vacuum line off or an earth off, recheck, double check down the list of possibles.......... good luck.

Mmm I have been racking my brain if I have missed something. But the first time I noticed it was a few weeks after changing the air intake.

So since noticing it I have done the following:
- Changed the air intake to the pod/airbox I originally had on the 6cly
- Fitted the Walbro GS341 in tank pump
- Fixed my wideband sensor wiring (Previously the car was running full rich as there were no HEGO signals to the ECU)
- Fitted areopro wiring harness for steering wheel controls.
- Blown and replaced the stereo fuse and the door lock fuse. Also, replaced parkers.
- Fitted another clock spring to try get cruise control working. Was a pin on the Clutch disengagement wiring.
- Had new exhaust fitted. (One lead was not on properly from this and was causing a huge misfire)
- Fitted new plugs/Leads


Going to try the coil packs tonight and then I think it will be fuel pump/filter/injectors and fuel rails.

Failing that I think a new car...

[mif73]

Have you tried using your QH to log inputs as you drive with a laptop?

You could probably check if the tps is working ok at time of flat spot etc.

Otherwise use a multimeter to measure ecu inputs as you drive?

Best of luck and please post your fix once you find it.

Cheers.

[bartsau]

Originally Posted by mif73

Have you tried using your QH to log inputs as you drive with a laptop?

You could probably check if the tps is working ok at time of flat spot etc.

Otherwise use a multimeter to measure ecu inputs as you drive?

Best of luck and please post your fix once you find it.

Cheers.

Have a fair few logs from the last day or 2. Have not had time to check over them yet. Will check them tonight. Going to try a different ecu tomorrow without the qh purely to rule it out. ( I have a manual xr8 ute ecu) wont run 100% but will certainly rule out qh issues.

Also l am going to change coil packs and oxy sensors. Just trying to get it back to a point before it had issues.

[Ride]

Money would still be on a spark issue. I had MSD leads a while ago, were OK new but after 20k on them they went to ****.

Bought a set of ICE leads earlier this year, fixed the miss I had and have performed flawlessly since (done 15k since). Nathan (FAT245) has also used livewires with success as well, definitely don't skimp on spark related gear!

[FTe342]

What about the camshaft synchroniser? Often the source of a miss in the mid range
Plenty of threads about it/replacement on here

[bartsau]

Originally Posted by FTe342

What about the camshaft synchroniser? Often the source of a miss in the mid range
Plenty of threads about it/replacement on here

Mmm well will look it up and try that.

Changed my coil packs and oxy sensors over back to the original items this morning and had no luck. Same issues again...
Then I went to my mechanic this morning and can't swap the ECU to rule out the qh as he can't get the scan tool to talk to anything except the ECU...

So considering this was not an issue 12 months ago I am seriously thinking there is something else more sinister going on. Actually thinking about pulling it off the road. Pulling the dash out and checking the entire wiring over front to back.

But before that I will try a couple more things and see how they go?

[BLU-220]

With msd coils, you have to use standard plugs, no iridium, or any other super-duper plugs, with the leads they have to be spiral wound not solid core leads

Cheers dean

[bartsau]

Originally Posted by AU2GHIA

With msd coils, you have to use standard plugs, no iridium, or any other super-duper plugs, with the leads they have to be spiral wound not solid core leads

Cheers dean

Why is this the case?? Have never heard of this before. And the leads are spiral wound too

[BLU-220]

sorry i was talking about when you have the msd dis4 units installed

[rayban76]

I'm running the MSD coil packs with Iridium plugs and spiral 10mm leads in my wagon and it works better than anything else I've tried

[Evgeni]

Just an idea to try and solve this one, if you can either access the o2 signals, either via a scan tool or by directly backprobing the sensor, you will at least be able to get some direction on whether it is fuel or spark.

At WOT, the mix should be rich. If it was a fuel issue, then the system may run lean. Good thing is with a V engine, you can compare one bank to the other.
With a spark issue, the system may take longer to return to stoichiometric once the throttle is lifted as fuel clears out of the exhaust.

If it all checks out, you can then start sussing out your sensors.

[Evgeni]

The other thing you can try is restrict the fuel return line with a clamp and see if it produces the same symptoms. This will maximise fuel pressure in the case that you are having a fuel issue at higher rpm.

[bartsau]

Well I am still chasing my tail on this issue to say the least....


I have now put the standard fuel pump back in and that changed nothing at all.

I have also, separately tried 2 different Throttle Position Sensors and 2 Different MAF's all with no luck same problem persists...

So accelerate and at approximately 4000rpm it 'hits the wall' ie stops gaining power at the same rate and feels like a 2tonne trailer has just been hitched...

It also has this same feeling whenever I am too heavy on the throttle.

Also, when sitting still in neutral giving it a few simultaneous revs it seems to every now and then 'backfire?'. Sounds like it is coming from the left set of headers. There is a couple of minor things I wanted sorted out on the exhaust so I will go back there and quiz the guy about it and get him to check it out as I am not interested in pulling the exhaust apart myself. This thing has already taken up hours and hours of my time so far....

I am wondering if this could maybe be a blocked catalytic converter? I know the exhaust is new but it doesn't mean I couldn't have picked up a dodgy cat?

[Ride]

Still sounds like an ignition issue of some sort. Have you got a set of known good leads or can borrow some off a mate?

Other thing could be plug gap, 1.3mm is the recommended.

[Evgeni]

A restricted exhaust could give these symptoms. Unscrew your O2 sensors to give the exhaust gas somewhere to go and see if you get the same issue. The computer ignores the O2 sensors at WOT anyway, so you wont create any new problems for yourself.

[bartsau]

Originally Posted by Ride

Still sounds like an ignition issue of some sort. Have you got a set of known good leads or can borrow some off a mate?

Other thing could be plug gap, 1.3mm is the recommended.

Plug gap was checked when I out the plugs in and they were all good. Leads are brand new. And although they arent the best they all measured less resistance than the originals.

Will try pulling out the oxy sensors and see if that makes any difference...fingers crossed.

Also, forgot to mention in my last post but when it 'hits the wall' the fuel oulse width drops down??

[Evgeni]

A reduced pulse width suggests that the computer is controlling it. Can mean that it is doing this because of the information that it is getting i.e from a sensor. Do you know if it is happening on all injectors?