developed a mis under load
- Thread starter Mick
- Start date
Paul Thompson 'Hooligan'
Admin
Hi Mick-
Do you get any other indication of the missfire? - i.e. the tacho 'kicks' a bit, or any other electrical indication..
Also - have you tried interrogating the ECU whilst running (passenger with laptop?) or downloaded any logged data. Often you can identify the cause of the missfire from the ECU's recorded data.
Do you get any other indication of the missfire? - i.e. the tacho 'kicks' a bit, or any other electrical indication..
Also - have you tried interrogating the ECU whilst running (passenger with laptop?) or downloaded any logged data. Often you can identify the cause of the missfire from the ECU's recorded data.
Hi paul, I have had the laptop incar but forgot to check while driving(no passenger). Just check the resitance of the leads they all seem to read between 1400 & 2100 ohm depending on there lengths, so i'm thinking they are ok. I did have what i thought was a fuse problem a couple of days before that shut down my low pressure fuel pumps. Now I am wondering if its the fuel filters. They have not been changed for about 7000km. Could be a doggy injector.
I'd check out the ignition coil too. The resistance specs vary depending upon the type of coil.
If you have a resistor in the 12v lead to the coil, you can rig a temporary bypass to feed it a full 12v. If that stops the misfire, you have a weak coil..
If you have a resistor in the 12v lead to the coil, you can rig a temporary bypass to feed it a full 12v. If that stops the misfire, you have a weak coil..
Pat Buckley
GT40s Supporter
I echo Randy's thoughts.
If the air flow is out of sync between the throttle bodies you'll get a mis fire or cough through the throttle body. I don't know if this is your problem, just something else to check. REDLINE SYNCHROMETER
TWM Induction OFFICIAL Authorized Dealer - Thor Motorsports - Competition/Street Fuel Injection Systems and Accessories
TWM Induction OFFICIAL Authorized Dealer - Thor Motorsports - Competition/Street Fuel Injection Systems and Accessories
Paul Thompson 'Hooligan'
Admin
Cleaning or checking/changing the fuel filters is definately a good idea - a restricted fuel delivery problem will definately be more prominant under load.
Shorting any coil ballast resistor fitted would be a good idea, although I would guess you have none fitted if ignition is controlled/fired by ECU.
Injector failure is always a possibility but less likely in my experience unless you've managed to allow debris into the fuel rail and as it's managed some 7000 km reliably thus far I'd still think they are ok - esp if the quality of idle has not changed at all.
If you hook up the laptop in the passenger seat (no I don't recommend looking at it whilst driving) - start up, go to the diags/errors page - rev up a few times to ensure no errors are reported off load - go for a drive - and once back or pulled over, have a look again at the screen to check for no reported errors. If you have hall effect triggers/pickups, it should be possible to have a 'spirited' drive with no errors indicated at all. In my experience, mag pickups will always indicate the occasional error but will not normally affect the smooth running of the motor.
Let us know how you get on..
Shorting any coil ballast resistor fitted would be a good idea, although I would guess you have none fitted if ignition is controlled/fired by ECU.
Injector failure is always a possibility but less likely in my experience unless you've managed to allow debris into the fuel rail and as it's managed some 7000 km reliably thus far I'd still think they are ok - esp if the quality of idle has not changed at all.
If you hook up the laptop in the passenger seat (no I don't recommend looking at it whilst driving) - start up, go to the diags/errors page - rev up a few times to ensure no errors are reported off load - go for a drive - and once back or pulled over, have a look again at the screen to check for no reported errors. If you have hall effect triggers/pickups, it should be possible to have a 'spirited' drive with no errors indicated at all. In my experience, mag pickups will always indicate the occasional error but will not normally affect the smooth running of the motor.
Let us know how you get on..
Mick,
You have elimated the plugs. I would hook up the laptop and start on the data output. If your misfire roams on one bank of cylinders it's like Al said your out of sync and that would eliminate your wires. If the data shows just one cylinder it narrows it down to injector (sticking or impedence) sparkplug lead(internal crack causing arcing)or weak coil(usualy the cylinder with the longest lead and highest impedence acts up). All the info the guys have given you could be the problem, it's how you interpet the data from ECU logger that will help you narrow it down so you don't end up changing everything and still have the same problem.
Dave
You have elimated the plugs. I would hook up the laptop and start on the data output. If your misfire roams on one bank of cylinders it's like Al said your out of sync and that would eliminate your wires. If the data shows just one cylinder it narrows it down to injector (sticking or impedence) sparkplug lead(internal crack causing arcing)or weak coil(usualy the cylinder with the longest lead and highest impedence acts up). All the info the guys have given you could be the problem, it's how you interpet the data from ECU logger that will help you narrow it down so you don't end up changing everything and still have the same problem.
Dave
Howard Jones
Supporter
Here's a easy one to check. If your motor is high enough in compression as to require premium octain fuel it is possible that the gas you now have onboard is the low octain stuff. Not because you bought it but because the station either got it wrong or got greedy. The gas may have also been comtaminated with water. Water in a filter will do what is happening to you.
Anyway it's pretty easy to check. Drain one tank,refill, and change/clean the filter for that side and do a back to back test.
Bad/wrong gas will have the greatest effect under load.
Anyway it's pretty easy to check. Drain one tank,refill, and change/clean the filter for that side and do a back to back test.
Bad/wrong gas will have the greatest effect under load.
Jac Mac,
I would have done that first when I went to the trouble of changing all the plugs. The data from the Motec box should give him a good indication of what cylinder-s is giving him the problem. I really don't what software they supply and how powerful it is or the ECU box itself. Does he run Iridium plugs because some ECU's have a curcuit and programing that measure cylinder temp and combustion through the plug itself. The software should map which cylinders are not up to parr(out of range).
Dave
I would have done that first when I went to the trouble of changing all the plugs. The data from the Motec box should give him a good indication of what cylinder-s is giving him the problem. I really don't what software they supply and how powerful it is or the ECU box itself. Does he run Iridium plugs because some ECU's have a curcuit and programing that measure cylinder temp and combustion through the plug itself. The software should map which cylinders are not up to parr(out of range).
Dave
Thanks for the input guys, It feels like a miss in one cylinder only. The headache is trying to isolate which one has the miss. Idle is ok all cylinders firing, under acceleration it starts to miss which would indicate maybe fuel delivery problem. Randy I didn't think the coil would be a problem as it seems to be with one particular cylinder just hard to isolate. I will take a look at the coil and run an injector test through the ECU. I dont know of an easy check.
Paul Thompson 'Hooligan'
Admin
If you're convinced it's a problem with just one cylinder - you could try pulling the power feed to one injector at a time, run on 7 cylinders and note when the problem stops.
If it doesnt stop then it's not isolated to a single cylinder - check ignition amp / kinglead / coil / distributor cap / rotor arm.
If it does, then you'll know which lead / plug / injector / cylinder has a problem.
I've seen a missfire caused by a pin within a connector not located correctly. On injector connection and ignition amp either will give a missfire if they randomly go open circuit, sometimes only occurring when a certain rev specific resonant vibration is reached. Can sometimes be checked by running engine at idle and giving all connections a good wiggle/pull...
If it doesnt stop then it's not isolated to a single cylinder - check ignition amp / kinglead / coil / distributor cap / rotor arm.
If it does, then you'll know which lead / plug / injector / cylinder has a problem.
I've seen a missfire caused by a pin within a connector not located correctly. On injector connection and ignition amp either will give a missfire if they randomly go open circuit, sometimes only occurring when a certain rev specific resonant vibration is reached. Can sometimes be checked by running engine at idle and giving all connections a good wiggle/pull...
If it's a matter of a mis-fire on one cylinder then I would think the delta would show up in the condition of that particular cylinder's spark plug, particularly since you should have pretty precise fuel and spark mgmt with the systems you have (producing consistency across all cylinders and plugs). You could perhaps go for a spirited drive and shut her down after an acceleration run and coast to a stop, pull the plugs and see if there's a semi-fouled plug.
Ok I have eliminated plugs and leads, not sure about injectors but a few day before the problem started I changed the injection timing map in in general setup/Misc. setup/inj timing table from just Rpm dependent to Rmp & Eff. point dependent without ajusting any of the table. does anybody know if this would cause a miss? me thinks so.
Dutton
Lifetime Supporter
Mick,
I generally avoid commenting on issues like the one you're experiencing due to the number of extraordinarily knowledgeable and talented forum members who offer spot-on comments… but this time I believe I’ll toss in a thought.
For whatever it’s worth, many years ago I was having similar issues with the ignition breaking up as the revs were climbing. It turned out to be a faulty distributor cap. I could hardly believe it.
Best,
T.
I generally avoid commenting on issues like the one you're experiencing due to the number of extraordinarily knowledgeable and talented forum members who offer spot-on comments… but this time I believe I’ll toss in a thought.
For whatever it’s worth, many years ago I was having similar issues with the ignition breaking up as the revs were climbing. It turned out to be a faulty distributor cap. I could hardly believe it.
Best,
T.
Paul Thompson 'Hooligan'
Admin
Hi again Mick -
Can you confirm that you are running sequential injection, ie all injectors are individually wired and not batch/group fired.
That you have both cam and crank timing signals functioning ok.
The rpm/eff selection you have made allows you to fine/tune the end point of injection within each cycle, which in turn allows the power/emissions/idle and driveability to be controlled more effectively (optimised). I have not come across an engine where enabling this feature caused a miss-fire and the motor should be able to run smoothly without it being selected and the injection timing being just linked to rpm.
It is also only used for sequential operation.
You could always disable it again to be sure, or re-load a previous backup map that was used before the problem appeared.
Out of interest - how about mailing me the config file you are using as I'd be interested in taking a look at your setup..
(paul.thompson at smart-tech-services.co.uk)
Can you confirm that you are running sequential injection, ie all injectors are individually wired and not batch/group fired.
That you have both cam and crank timing signals functioning ok.
The rpm/eff selection you have made allows you to fine/tune the end point of injection within each cycle, which in turn allows the power/emissions/idle and driveability to be controlled more effectively (optimised). I have not come across an engine where enabling this feature caused a miss-fire and the motor should be able to run smoothly without it being selected and the injection timing being just linked to rpm.
It is also only used for sequential operation.
You could always disable it again to be sure, or re-load a previous backup map that was used before the problem appeared.
Out of interest - how about mailing me the config file you are using as I'd be interested in taking a look at your setup..
(paul.thompson at smart-tech-services.co.uk)
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