Curious running problem...limp mode?

[marcoos_1]

I took the car out today for the first time (see recent newbie in ayrshire thread...) and, among other things (which I will no doubt ask about later), I have the following problem:

when the car does circa 4000rpm, the engine seems to go into some kind of "limp mode" or restricted power....almost as if running on 2 cylinders. It will not rectify itself no matter what I do, unless I switch off, and reset the immobiliser. As soon as I do this then it's running a treat.

I have heard about some mind of "misfire detection system" on the VVC that can apparently be bypassed? Does anyone know anything about this or how I can eliminate this as the fault? It seems like a likely candidate as opposed to distributor cap/leads/plugs etc, as the car runs sweet as a nut until it does this, then wont clear, then runs great again the minute I stop and reset?

Thanks in advance for any help you guys can offer.

Mark.

[s29ttc]

Could the issue not still relate to the coil pack, HT leads, Spark plugs or even a Lambda sensor issue or something similar and be related to the load? I think the misfire detection unit is there as there was potential issues for the cat to catch fire so I would be checking out the potential sources of misfire prior to bypassing. With the car siting for so long there could be some things causing the car to misfire whilst under load hence your experiencing it at higher rpm???? I don't know the best way to diagnose but could you find someone with a spare good coil pack and change it and see if it cures the issue or even bite the bullet and change it over for good measure? With it sitting for so long might not be a bad idea to change the coil, leads and spark plugs but may not sort your issue. The misfire detection unit is in the boot, not sure if it's simply plug the cable before and after into one another.

[s29ttc]

Have a look at this link which may be of assistance

http://wiki.seloc.org/a/Misfire

[robin]

If it is a VVC then the misfire detection kit might be bust (ironically causing the very problem it's designed to detect), or you may not have the kit fitted (it was a recall/retrofit) and you may have the actual VVC misfire - caused, I believe, but interference between the HT lead system and one of the engine rotation sensors (cam or crank).

Assuming it's still running the Rover 2.J ECU then I think you should be able to get engine management data over the ECU data link to find out what's happening - most independents probably have a Rover ECU diag tool of some sort these days.

Cheers,
Robin

[marcoos_1]

OK, time for a quick update.

I've done the battery lead/earths, changed the fuel filter and fitted a de-cat pipe (I got one with the car anyway). I've also given it a full tank of fresh fuel and some injector cleaner......no difference at all. I've tried getting the local garage to do a diagnostic check, but it wouldn't connect as he reckons the OBD connector in the boot is a bit corroded. Any ideas for cleaning in situ? I've sprayed it with electrical contact cleaner but the bottom pins still look a bit green.

[robin]

It's possible that the tool the garage is using won't understand the MEMS2.J - you really should take it somewhere that they are confident of being able to read that ECU - i.e. they've read one before. That way you can be sure the issue is in the connector.

Alternately, if you have the misfire detection kit fitted, you could try to remove it ... it is inserted into the original loom, etc. A quick google might reveal instructions on how to remove it. You can always put it back afterwards.

[robin]

P.S. the condition you describe is normally associated with the ignition system - nothing you've changed has anything to do with the ignition system.

I would be looking at coil pack (down underneath the inlet manifold, twin coil pack), leads (very sensitive to leads, so buy the proper items, not some cheap junk), spark plugs. The leads and plugs are service items, so I would start with them. The coil pack is pricey and hard-ish to change, so that would be later.

But start with ripping out the misfire detection kit if fitted, 'cos it's pants according to the internet Also if your ECU diag plug is green with corrosion, what state is the misfire detection plug in - if also soaked then it's probably bust.

There are many other things it could be. You need somebody that knows what they are looking at, or you will simply replace all sensors/ancillaries only to discover it's a broken wire in a loom somewhere ...

Cheers,
Robin

[marcoos_1]

Yes, couldn't agree more. Problem is sometimes finding that right person. I definitely don't want to start chucking sensors at it without really understanding the issue. I've been out in the garage for the past hour or so just sniffing around it. After a bit of googling I found what I think is the misfire detection unit on the near side boot wall. About fag packet size with a purple lock on the plug. I disconnected as per one of the threads I read, but the feckin thing wouldn't start.....so I don't think it's as easy as just taking the plug off. It turned over OK, but no firing, so it obviously didn't like that.

The actual connect and wires look in pretty good shape. The OBD socket is perhaps the worst as the previous owner didn't replace the rubber bung and the cap on it (but at least I found the cap in the boot. I'll give it a good clean tomorrow and then see if I can get the guys reader to interface with it. He has three different systems in his workshop and they listed Rover/MG/VVC and he says he has done this before. He's less than a mile from the house so I'll give him a go before I go further afield (although not too sure who too).
The car has new Magnecor leads......I did read on another thread that the VVC didn't like Magnecor leads.....but there's so many opinions its hard to pick through it all. If I was to change them then I'm not too sure where I would get "OEM" leads as someone suggested? Surely the leads from Lotus can't be that magically different can they? (I also read that Lotus buy them from Rover!).

I'll do some more digging meanwhile on removing the Misfire Unit......I'd like to at least rule this out. They seem to be nothing but trouble anyway....

[Ferg]

Is there a way to connect a known good coil pack up to test?

[robin]

Hi,

You want genuine rover leads to avoid any confusion.

You cannot just unplug the misfire detection unit [MDU] - you also need to reconnect the original loom - the MDUwas an after sale fit/recall fit.

To fit it they put the MDU in the boot. It comes with a loom. The big plug on the loom connects to the MDU. The small ends on the loom connect to various sensors in the engine bay and the original engine loom plugs are disconnected from those same sensors.

Here's a picture from somebody selling one on eBay. It looks like about 5-6 connections in the engine bay.



You would trace the loom bundle through the grommet in the bulkhead into the engine bay and follow each sub-loom to the sensor; before disconnecting I suggest you label the connector (get a dymo or similar) and take a picture of it connected; normally a close up and a picture from further back is useful; the close up for details of which way the connector fits, etc., the further back is more for context in case you cannot remember where to plug it in!

Now for each plug you disconnect you would need to re-connect the original plug which ought to be dangling around nearby. Unfortunately I've never even seen one of these things, and I cannot find a wiring diagram on the internet, so I cannot be sure it's as simple as unplug MDU, replug original stuff.

Cheers,
Robin

[robin]

Is there a way to connect a known good coil pack up to test?

You can test the coil for continuity; the low tension side should see a fairly low but non-zero resistance between the live and switch signals (you have to unplug the loom and measure at the coil terminals). As there are two coils, you need to do this twice. The HT side should see a higher but non-infinite resistance between the two coil "king pins". Note that it's also possible that the two kings pins are shorted (0 ohm resistance to one another) and that the higher resistance will be between the king pins and the engine block earth - I don't know specifically how the VVC coil is wired.

P.S. If you're ingenious you can measure the coil impedance from the ECU plug and the spark plug leads, so you don't have to ferret about in the awkward to reach area that the coil pack lives ...

P.P.S. Given it runs OK to 4K I suspect the coil impedance will measure OK ... the coil might still be at fault, but you won't detect it with the engine off.

[marcoos_1]

OK, thanks again for your help.

I guess at this stage yet another set of leads would be a simple change. Now for a stupid question.......where do I get genuine Rover leads? I'm guessing if I order through local factor like Eurocarparts then I won't get the right thing. I checked Eliseparts, but they only list "Rover Leads" for the S2 K Series......the S1 VVC/Elise/Exige leads are Magnecor which is what I fitted. I'm guessing there aren't any Rover dealers left now, so where do you recommend?

Meanwhile I'll try and clean the OBD plug as best I can for another shot at hooking it up to a diagnostic machine.

[woody]

Try Rimmer Bros (actual name) for Rover parts.

While my car isn't a VVC & therefore has a different set up, I've had a few misfire issues over the years. At one point I had very similar symptoms to those you describe. After a lot of head scratching it turned out to be the HT lead from the (single) coil had chaffed on it's way past the water pipes on the rear of the engine. New lead fixed. Had another misfire that would randomly affect the car a couple of years ago, sometimes for a while, sometimes for a minute or so. Replaced the entire HT system 1 part at a time with the leads being last as I'd recently fitted new Bosch leads.... it was the leads. Found some OEM Lucas ones from ebay that did the trick.

[marcoos_1]

great....I'll get onto Rimmer Bros now, might as well get a set up and give it a go.

[marcoos_1]

leads ordered......should be here tomorrow. fingers crossed........thanks for all your help and suggestions