Chasing the multiple misfires
Thread Starter
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Winching
Joined: Aug 2012
Posts: 645
Likes: 258
From: San Mateo, CA
Not quite sure how to raise idle speed on a D2, but maybe another Forum member knows an easy way. A simple way to try is to tighten the throttle cable adjustment until the throttle plate opens slightly. Be advised, this might cause other issues (e.g. on D1 causes really high idle 1500 - 2000 when started) or throw a different code if the Adaptive Values (i.e. TPS initial value) are not reset. The ECM will attempt to adjust the IACV to a pre-set RPM, so any adjustment of the cable will need to overcome the IACV limit.
Pay attention to the pre-test position of the throttle cable so you can restore it later. Usual setting is to back off until the cable just goes slack, plus a little. Now that I write this down, it seems a bit complicated to me for little gain. Successful result of the test would be smoother idle RPMs (no more lope) so no more misfire codes. Then just put everything back to the starting point with no resolution of the problem. Maybe not worth the effort to gain a little knowledge.
Maybe just clear the codes then put a brick on the gas pedal (850 - 950 rpm), to see if the misfires do not re-appear during a long warm up and idle. Just rambling now.... Keep calm and Rover on!
Pay attention to the pre-test position of the throttle cable so you can restore it later. Usual setting is to back off until the cable just goes slack, plus a little. Now that I write this down, it seems a bit complicated to me for little gain. Successful result of the test would be smoother idle RPMs (no more lope) so no more misfire codes. Then just put everything back to the starting point with no resolution of the problem. Maybe not worth the effort to gain a little knowledge.
Maybe just clear the codes then put a brick on the gas pedal (850 - 950 rpm), to see if the misfires do not re-appear during a long warm up and idle. Just rambling now.... Keep calm and Rover on!
The idle speed is programmed in to the ECM and controlled by the IACV, that is why it is throwing the idle code. Multiple misfires will not be cured by idle speed. Is that still the only code? No consistent cylinder codes? Its been a long thread, can you summarize again the new parts and things you have tried? I seem to remember coils and wires were in there somewhere, along with some other new bits. Have you tried unplugging the MAF ? Yes it will throw a maf code but it forces the ecm to use only the 02's for fueling and sometimes the maf's on these confuses itself. Your fuel trims and 02's look ok, so not far away from running well.
Thread Starter
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Winching
Joined: Aug 2012
Posts: 645
Likes: 258
From: San Mateo, CA
The idle speed is programmed in to the ECM and controlled by the IACV, that is why it is throwing the idle code. Multiple misfires will not be cured by idle speed. Is that still the only code? No consistent cylinder codes? Its been a long thread, can you summarize again the new parts and things you have tried? I seem to remember coils and wires were in there somewhere, along with some other new bits. Have you tried unplugging the MAF ? Yes it will throw a maf code but it forces the ecm to use only the 02's for fueling and sometimes the maf's on these confuses itself. Your fuel trims and 02's look ok, so not far away from running well.
I put the throttle cable back to normal after getting the idle code and it has not been back.
Yes, the only codes are misfires. The latest were all at the same time - 1,2,3,4,5,7,8.
New parts include plugs (NGK BPR5EIX), new STI wires, and a new Bosch MAF sensor. Coils and CrankPS are 2 years old (Bosch/Genuine LR), and the injectors are rebuilt, also installed 2 years ago. New Magnaflow stainless steel Y pipe/cats and new Bosch upstream O2 sensors.
I took the CrankPS out a couple of weeks ago to make sure it was installed correctly and properly plugged in/seated. No change.
The builder, TWS, sent me the long block with new Champion copper plugs. That was the first thing I changed as I was getting misfires from the very start.
No, I have not tried unplugging the MAF. I can certainly give it a go, but what would we be trying to verify/accomplish?
Pretty frustrating as she runs very well - except for the bumpy idle and misfire codes. No hesitation launching, no knocking, and great power. Averaging 13.2 MPG. Also runs steady at about 186F.
Thanks again for all the help!
Last edited by Tony Luna; Mar 25, 2025 at 07:44 AM.
Pro Wrench
Joined: Apr 2018
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From: SE PA
Are you running high octane fuel? I'm not sure what a 4.0 crank with 4.6 pistons will do to compression but if it's raising it (my guess is that's the intent) then high octane fuel will be required and more importantly you may want to reexamine which spark plugs are appropriate. NGK gets hotter as the number goes down and you might want to try something colder than the cross to the stock Champions. 5 seems pretty hot to me, you might try 6s or even 7s. Misfires are preignition and/or detonation, and those are two ways to address it in a modified engine. It would be worth inspecting the knock sensors as well since those are responsible for reporting the misfires.
Thread Starter
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Winching
Joined: Aug 2012
Posts: 645
Likes: 258
From: San Mateo, CA
Are you running high octane fuel? I'm not sure what a 4.0 crank with 4.6 pistons will do to compression but if it's raising it (my guess is that's the intent) then high octane fuel will be required and more importantly you may want to reexamine which spark plugs are appropriate. NGK gets hotter as the number goes down and you might want to try something colder than the cross to the stock Champions. 5 seems pretty hot to me, you might try 6s or even 7s. Misfires are preignition and/or detonation, and those are two ways to address it in a modified engine. It would be worth inspecting the knock sensors as well since those are responsible for reporting the misfires.
As high as I can get in CA - 91. And yes, the 4.0 pistons on 4.6 rotating assembly does give a slight bump in compression. I was running the same set up (4.0 pistons / 4.6 rotating assy) in a pervious build (2 years ago when I got all the new parts) with the same plugs and 91 octane and did not have any misfire issues then. I forgot to mention that I also replaced the knock sensors two years ago as well. Most all of the connectors under the hood were replaced back then too; all meticulously soldered and covered with marine grade heatshrink. Wiring on this truck is as good as new - or maybe better. The last build ran well too until a head gasket blew - probably due to a stud that gave out - back story here https://landroverforums.com/forum/di...y-area-125179/
I have not heard any knocking or pinging. But cooler plugs may be worth a shot... Willing to try anything at this point.
Thread Starter
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Winching
Joined: Aug 2012
Posts: 645
Likes: 258
From: San Mateo, CA
BTW, did the log file I sent come through OK? And thanks in advance!
Last edited by Tony Luna; Mar 25, 2025 at 09:32 AM.
Pro Wrench
Joined: Apr 2021
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From: SE Washington State
My understanding is the misses are generated during idle, not while driving under load. Correct? That may rule out knock, but higher octane (or an additive) is an easy thing to try. Also easy to try the MAF disconnect.
Interesting no miss on 6, maybe a clue. What does the builder have to say about this issue? You have a lot of brain power working with you. Maybe take a look at the reluctor ring on the new flexplate to make sure all the pins are straight/properly spaced. There's a little tool gauge made to measure the gaps if you go that far.
Interesting no miss on 6, maybe a clue. What does the builder have to say about this issue? You have a lot of brain power working with you. Maybe take a look at the reluctor ring on the new flexplate to make sure all the pins are straight/properly spaced. There's a little tool gauge made to measure the gaps if you go that far.
Thread Starter
|
Winching
Joined: Aug 2012
Posts: 645
Likes: 258
From: San Mateo, CA
My understanding is the misses are generated during idle, not while driving under load. Correct? That may rule out knock, but higher octane (or an additive) is an easy thing to try. Also easy to try the MAF disconnect.
Interesting no miss on 6, maybe a clue. What does the builder have to say about this issue? You have a lot of brain power working with you. Maybe take a look at the reluctor ring on the new flexplate to make sure all the pins are straight/properly spaced. There's a little tool gauge made to measure the gaps if you go that far.
Interesting no miss on 6, maybe a clue. What does the builder have to say about this issue? You have a lot of brain power working with you. Maybe take a look at the reluctor ring on the new flexplate to make sure all the pins are straight/properly spaced. There's a little tool gauge made to measure the gaps if you go that far.
Yes, misfires appear while at idle - not under load.
Octane boost is a good idea and easy - I'll give it a shot.
Curious, what will disconnecting the MAF do?
5 was absent too - until recently. But they all come at once after warm up and left to idle for a while. The consistent offenders are 1,2,3,4,5,7,8.
The builder, TWS, who I trust, says the compression and cam aren't big enough to cause issues.
I've been running the Ashcroft flex plate for a while - but no reluctor rings. Do you mean the flywheel?
Tempted to shotgun out the CrankPS, but it is expensive...
Last edited by Tony Luna; Mar 25, 2025 at 10:42 AM.