Misfire Flashing Check engine only at Idle

[malonso123]

i have aDisco2 with 172K
just changed wires, plugs and O2 sensors (Boch) about 500 miles ago.

it started misfiring on cylinders 3, 5, ,and 7 also have codes for O2 sensors and adaptive fuel mixture.
it runs fine 100% of time on the highway and 95% when in traffic. Only when idling in traffic does it misfire and make the check engine light flash. Just started about 1 week ago.

i am going to check that the wires are secure on the plugs and coil today, but any thoughts?

Thank you in advance.

 

[Swedjen2]

What's the rust situation on your rig? Make sure all your ground wires are clean and tight.
Check your charging system while your at it. Could be a battery/alternator issue.

 

[kennith]

You don't have those Bosch Platinum +4 plugs or a K&N filter, do you?

Even if not, it could be a failing or dirty mass airflow sensor. That can cause all manner of strange codes and behavior before the vehicle just says "fuck it" and throws you into limp mode; certainly at lower revs. It wouldn't hurt to spray it out with the cleaner available at any part store and see what happens.

That spray is useful for all kinds of things, so it's not a total loss if you don't end up using it all.

There's other stuff it could be, but that's a pretty easy check, and probably not an expensive "drop one in just to see" affair, if you end up having to do it for diagnostics. Tillery will almost certainly have one off another vehicle that works.

All on one bank, though... It could also be something a little more insidious, as there are occasional head gasket leaks toward the rear, or simply a coil that's faulty.

Cheers,

Kennith

 

[malonso123]

i forgot to mention that i also replaced the MAFS. i will go check out the ground wires.
Thank you Both.

 

[kennith]

i forgot to mention that i also replaced the MAFS. i will go check out the ground wires.
Thank you Both.

Check that connector, then. They seem to hold up well enough, but they are indeed kind of cheesy. I've never seen any trouble, but to be honest I've always expected that I'll encounter it eventually. Maybe not, but it's worth a look.

You'll really want to check the coil packs, as well. There are several tests you can find with searches on the web with pictures and all that. Explaining the stuff here may not be sufficient. Work your way from the plugs back, because the coils are incredibly hard to reach for many people.

I don't remember which one handles which cylinders, but diagrams are easy to find. People don't seem to have trouble, but I know I've been through a few; then again, I've been on a hell of a lot of washboard roads. That does strange things to a car over time.

There are only two, and each handles four cylinders. If you want to actually see the things they're jammed between the firewall and the engine at the top, behind the intake manifold and all that. It's like a strip club, though. Look all you want, but quite often you can't touch.

Cheers,

Kennith

 

[Swedjen2]

I've got 155K on my '04, but the engine was rebuilt about 8K ago. D&D machined block with top-hat liners, Wedgeshop cam, heads were rebuilt, but not sure if they have big valves or not.
It was done by the PO.
I have had a rough idle and the CEL come on about every tank o'gas. The OBDII says it's the P0300 general misfire, along with P0301, P0302, P0303, P0304, P0305, P0306, P0307 AND P0308 which are cyl's 1-8 misfires, but only at idle. Once it was off idle, it ran fine.
I finally brought it to a very good shop to see if they could diagnose the issue. It had been to two or three other Rover only shops to diagnose the issue.
I got a call a few hours ago and apparently, the PO didn't renew the injector o-rings. The shop called and said when they sprayed whatever they spray around injectors to see if there are any vacuum leaks or air getting sucked in around the o-ring and injectors, the CEL light would come on.
If you have 172K, you probably need an injector o-ring refresh as well. This is an easily overlooked source of poor running high-milage engines.
There are places that will test and rebuild injectors - if they can be salvaged - for pretty cheap.
Try these guys - https://hpinjectors.com

I'll send my original set to these guys and reuse them in my other D2 trail rig that needs an engine. (Got it cheap and all set for overland/trail runs - SafetyRack with the usual recovery gear, Lights F/R, Dual Battery, ARB bumpers front and rear, Sliders, lifted, and ARB rear locker.)

 

[discostew]

your misfires are all on the same bank. Your o2 sensor on that bank could be causing the whole bank to lean out so bad it misfires. Or you could have a vacuum leak on that bank.

 

[kennith]

your misfires are all on the same bank. Your o2 sensor on that bank could be causing the whole bank to lean out so bad it misfires. Or you could have a vacuum leak on that bank.

Yup. The bright side is it's all on one bank. I mean, it could be a dark side, too, but at least it narrows down diagnosis.

That probably knocks out a MAFS error, but I've seen it happen once on my own vehicle and take out one bank.

It's just an easy thing to check.

Cheers,

Kennith

 

[Swedjen2]

i forgot to mention that i also replaced the MAFS. i will go check out the ground wires.
Thank you Both.

Well, don't disappear on us.

"I got'sta know."

 

[malonso123]

ok, so i checked my o2 sensors and they seemed to be ok, but when i ran a diagnostic i had no reading from the downstream passenger side. Upon closer inspection i noticed that it seemed to be just shy of being all the way in. I unhooked it and noticed some grime build up. so i cleaned it out and reinstalled. The disco seems to be running well and i have not misfires so far. i will drive it around all weekend and see if that is what it was. i do have a new coil pack in case thats whats causing the misfires. but i am going to wait and see.
Thank you for all the input. i appreciate it.

 

[kennith]

Cool. I hope it sorts the issue for you.

Cheers,

Kennith

 

[discostew]

Yup. The bright side is it's all on one bank. I mean, it could be a dark side, too, but at least it narrows down diagnosis.

That probably knocks out a MAFS error, but I've seen it happen once on my own vehicle and take out one bank.

It's just an easy thing to check.

Cheers,

Kennith

Oh Kenny. If you had a misfire code down one bank you did not fix it with a mass air flow sensor. I hate to be the one who points it out but...I think you fixed that car by accident and then went out and bought a mass air flow sensor. God bless you Kenny.

 

[kennith]

Oh Kenny. If you had a misfire code down one bank you did not fix it with a mass air flow sensor. I hate to be the one who points it out but...I think you fixed that car by accident and then went out and bought a mass air flow sensor. God bless you Kenny.

Nope, it was certainly the mass airflow sensor. It had become a bit iffy, and that happened before complete failure.

No further service was performed, and no further parts were installed. I knew it needed one to begin with, so there was no reason to start anywhere else.

I swapped it out and got the bank back. Job done. It's an unlikely event, but it happened. Twenty thousand miles passed before I had to do any further repairs. It's possible another factor, such as an 02 sensor slightly out of specification contributed, but once that MAFS was replaced, I was good to go for several trips without a single issue.

If I'd lost something else within a couple thousand miles, I'd concede that another part was actually faulty or failing, but that's not how it went down.

Cheers,

Kennith