Finally having a continuous misfire on my E320 W124

[maxicab]

My 1 year of often very intermittent misfiring is now continuously present. It became permanent after running the car for several days with the MAF connector unplugged, which, because it was now running well, I thought had finally identified the source of the intermittent misfire.
On checking, there is a persistent absent spark on at the least front-most (no. 1) cylinder and possibly also on the rear-most cylinder (no. 6) - that one is the one under the coil so it is hard to test it. (any hints on how to do so?)
The misfire starts from cold and continues on thereafter, and is from warm start too. It has VERY poor power, esp uphills, and pulls like a wartberg or a morris minor on 3 cylinders, but on the flat, once up to speed, it can seem surprisingly OK unless you need to speed up! And it sounds like an electric lawn mower.
It has a strange smell while running, coming from under the car, and the rear of the catalytic convertor is glowing red. I guess this is due to unburnt fuel being dumped into the cat?
I swapped the rear coil for with another one, and then with an old coil but neither of these changes made any difference. I have also changed the long HT lead to the front no. 1 cylinder with an old lead but this made no difference. Also the presence or absence of MAF sensor and lambda sensor in circuit makes no discernable difference.
So I'm back to where I was in February, but at least it's now continuous, so I should be able to track it down finally. It seems like it just about must be the ECU now after all, but I just want to be sure before I remove it. Is there a multimeter or some other simple check that I can do on the LT coil feed from the ECU to the rearmost coil?
I am starting this as a new post, so please post any responses here, NOT on the previous intermittent misfire post; I am just mentioning it at the end of the former post so that anyone in the future can follow to "what happened next".
To briefly summarise, have had intermittent misfire for a year, new engine wiring loom, new HT leads x3, new plug to coil direct connections x 3, new plugs (2 sets), 3 sets of diagnostic tests, (later 2 showed nothing), new fuel filter, improved and checked various electrical connections. Many false hopes but no permanent cure.
Is the Isle of Wight guy still the best bet for ECU testing/rebuilding?

Thanks for any help, David

 

[stumpy]

I had very similar on my 280. Headgasket changed but still misfiring. Ecu swapped with a good one from another car and ran fine. Now on the search for a reconned ecu. Indie has done 3 this month. I'm slightly worried as to why it blew though.

 

[crammy69]

Have you looked at the EZL unit in the engine bay? ( assuming it has one same as my W124 300 24v) maybe its this rather than the ECU at fault?

I have been getting misfiring/lumpy running but only once engine warm, so plan to remove the EZL this weekend and replace/re-new the heat sink compound. I also replaced the fuel evaporation system charcoal filter under the front nearside wing last weekend as read on one site that could be a contributing factor to weir mis-firing. Alas no noticeable difference so far though.

Cheers

 

[maxicab]

Thanks, but I don't believe that I have an EZL - I have an HFM-SFI distributorless ignition - '95 E320. I read the fault codes today with a home-made LED Blink (Flash) tester. Where is your Indy located Stumpy?
At first I had the codes: 4 (MAF), 9 (O2 sensor), 11 (O2 sensor heater), 13 (O2 sensor control system operating at rich or lean limit), 23 (ignition output 2 or coil for cylinder 3 and 4), 26 (not used). These were repeatable.
Thought I was onto something, but couldn't see why a fault on cylinder 3 and 4 was recorded, but not 1 and 6, then also realised that I'd run the car without a MAF or the lambda oxygen sensor connected for a while during the week, to try and narrow down the (then) intermittent misfire.
So I reset all the codes, ran the car for a few minutes; misfiring badly the whole time, running like a sick Wartberg, re-read the codes and lo and behold: ......no fault found! (repeatedly checked this and same result).
So I still need advice please on:
1. How to tell whether the plugs below the coils are receiving spark.
2. How to check the coil feeds are supplying current to the coils (IE if the ECU is supplying output to all 3 coils)
3 Any other ideas for fault testing

Thanks, David

 

[stumpy]

Thanks, but I don't believe that I have an EZL - I have an HFM-SFI distributorless ignition - '95 E320. I read the fault codes today with a home-made LED Blink (Flash) tester. Where is your Indy located Stumpy?
At first I had the codes: 4 (MAF), 9 (O2 sensor), 11 (O2 sensor heater), 13 (O2 sensor control system operating at rich or lean limit), 23 (ignition output 2 or coil for cylinder 3 and 4), 26 (not used). These were repeatable.
Thought I was onto something, but couldn't see why a fault on cylinder 3 and 4 was recorded, but not 1 and 6, then also realised that I'd run the car without a MAF or the lambda oxygen sensor connected for a while during the week, to try and narrow down the (then) intermittent misfire.
So I reset all the codes, ran the car for a few minutes; misfiring badly the whole time, running like a sick Wartberg, re-read the codes and lo and behold: ......no fault found! (repeatedly checked this and same result).
So I still need advice please on:
1. How to tell whether the plugs below the coils are receiving spark.
2. How to check the coil feeds are supplying current to the coils (IE if the ECU is supplying output to all 3 coils)
3 Any other ideas for fault testing

Thanks, David

I use SS motors in Weybridge Surrey

 

[tjoneill@btconnect.com]

hi, a common problem with the 104 engine missfiring was the wiring to the coils, its moulded in rubber next to coils, have seen it all dug out and individually insulated or alternatively replace wiring,it can be sourced from dealer,it becomes brittle and brakes up

 

[hotrodder]

To test for a spark from the 'coil on plug' plugs you'll want something like THIS. The extension will let you check for a spark via a timing light (or whatever method you used on the other plugs)

Having just bought a 93 320TE a few weeks ago (and being more of an old car guy) i'm not yet familiar with the LT side of these systems to accurately describe which connections to test. However after testing all cylinders for a spark you can move a coil which IS firing its plugs to cylinders that are down and repeat- if the misfire stays put then you've eliminated the HT side

Remembering that i'm not fully clued up on modern car electrics/diagnostics... i doubt these cars are advanced enough to switch off injectors to cylinders without a spark (borne out by the red hot cat) so a consistant, even if intermitent, misfire is likely to result in various fault codes and may be of limited use unless experienced enough in auto diagnostics to differentiate between useful codes and those that are simply the result of a fault elsewhere.

 

[lakeside]

i doubt these cars are advanced enough to switch off injectors to cylinders without a spark

The HFM/SFI M104's (280 and 320) do indeed do this.

Maxicab, I think your ECU could be fried. It's the only bit you haven't replaced, and would easily be damaged by the old loom shorting out.

 

[maxicab]

Lakeside, I'm afraid I agree. Although I can't check the LT side of the coil, I'm now sure there's no spark to no. 1 or no. 6 cylinder. I didn't need that clever tool in the end Hotrodder. I swapped in another coil, still the same, then just lifted the coil up off from the cylinder, while it was running, so that the rubber stumpy connector below came off the plug below it, and it made no difference at all to the running. Then I replaced it all and just removed the LT coil lead and it made no difference. Since the wiring loom is new and there is nothing else between it and the ECU that I can find, I'm almost certain the ECU is fried (or scrambled). I'm now wondering about a home repair and seeing what I can find out. Thanks for all your help

 

[hotrodder]

My bad Re injecter control. Being new to these i wasn't sure how advanced these systems are (have since found out about the individual cylinder timing/trim) but given the glowing cat and lambda faults it made sense at the time. With everything that's been replaced i would be suspecting the ecu as well (especially if the loom problems were discovered after misfiring began) but it makes sense to thoroughly exclude everything else first- unfortunaly it sounds as though you've reached that point

If the ecu is supposed to switch out injecters on cylinders without a spark then the glowing cat + lambda 'limits exceeded' suggests the ecu doesn't 'know' that plugs are down i.e. it thinks it's firing them... The only other scenario i can think of would be leaking injectors (soooo rich that plugs are fouled) but to have that occur on two cylinders that share a coil, odds must be astronomical

 

[stumpy]

Lakeside, I'm afraid I agree. Although I can't check the LT side of the coil, I'm now sure there's no spark to no. 1 or no. 6 cylinder. I didn't need that clever tool in the end Hotrodder. I swapped in another coil, still the same, then just lifted the coil up off from the cylinder, while it was running, so that the rubber stumpy connector below came off the plug below it, and it made no difference at all to the running. Then I replaced it all and just removed the LT coil lead and it made no difference. Since the wiring loom is new and there is nothing else between it and the ECU that I can find, I'm almost certain the ECU is fried (or scrambled). I'm now wondering about a home repair and seeing what I can find out. Thanks for all your help

Give Joe at SS a call as he knows a guy who repairs them. Mine is still off the road sadly but I don't want to shell out 1200 for a new ECU

 

[maxicab]

Just to update - had a local tech guy - Mike Gander in Ringmer - do some diagnostics this week with the car misfiring away continuously. He found no or very minimal current in LT feed to rear-most coil. He's sure its the ECU output drivers causing the problem. I have done some further research here and have chosen Peter Remmington at King's Lynn (fp.remmington.plus.com/ind.htm) to send the ECU to. A very close second was the Isle of Wight people (carelect.demon.co.uk). Peter will test for £40 and report back; he says that these ECUs are usually an easy repair. Hope he's right! I have today removed it (Thanks Juddian) and packed it all up. Will keep you posted.
David

 

[maxicab]

P.S. Autotek -note spelling - and Lynx are strongly NOT recommended as places to send your duff ECU. Google either of these names with "ECU" and judge for yourself.

 

[Juddian]

Maxicab, check your pm box please.

 

[maxicab]

Just before I sent off the ECU I noticed the wiring hidden underneath the ECU was wet - so I hesitated for a few days to let it all dry out fully - and reinstalled the ECU yesterday and found no change in symptoms, so I sent the ECU off (finally!). Chose the IOW people this time after some further researches. I will keep you posted.

 

[maxicab]

I'm now £350 poorer but my car is running beautifully with no hesitation. Terrific service from Carelect.demon folk on the IOW. They say they rebuild several Merc ECUs every week! I'll post an update in a week or so but for now, all is wonderful. Thanks to all for advice, David

 

[lakeside]

Fingers crossed. Thanks for the updates.

 

[Juddian]

Looking forward to your report David, did the repairer give any explanation of what was wrong by the way?

Glad you are up and running anyway.

 

[ALAN@ECUCLINIC]

the main problem for ths merc miss is coil packs, we see loads of p.m.s and v.d.o ecu all with the same problem, most popular is 0261 200 614/612 but generally speaking ,they all suffer.

bosch type £420 inc carriage (no vat)

vdo type £380 inc carriage (no vat)

 

[maxicab]

Hi Alan
Are you saying the most common cause for a misfire in this model Merc is the coil packs, or that the most common cause for the ECUs failing in this model is the coil packs?
I would have expected you to say the commonest cause for ECU failure in this model is due to electrical shorts due to deteriorated engine wiring looms.
Do you get many sparingly intermittent faults such as mine was for 11 months (before becoming continuous) being due to an ECU fault?
I guess by "most popular" you mean the unit that most commonly fails?
Mine is the VDO type - 412.229/006/017, Merc No. 016 545 81 32 [02]
It seems that the £347 inc. VAT and carriage that I paid is actually pretty reasonable value then for a test and rebuild.
No, Juddian, no real explanation from them (Carelect, IOW) as to the actual fault. They just confirmed that it was indeed a faulty ECU and would need a rebuild as provisionally quoted for.
I have to say that I was as sure as I could possibly be that it was the ECU before I finally did send it off, but in retrospect, I should have sent it months earlier.
It really isn't as daunting as it seems if you have a likely ECU problem. Especially if the problem is intermittent and if you're struggling for a diagnosis, and have done all the obvious things and an ECU problem seems likely, it is probably worth it to just remove the ECU and get it tested!