M104 280 engine misfire.

[a lex]

Oh no The poor old girl is having some troubles!

96 S280 with the M104 engine - 130k miles, last serviced with new plugs and oil about 12k miles ago looking at the invoices.

Since buying her 10k miles ago she has had a very occasional stutter on warm idle - a single miss/burp and then back to normal, it didnt bother me at all.

In the last two days she has twice ran dog rough on me - once when ariving at work so I couldnt investigate and then again just now when arriving home - its probably not a coincidence that this happening after a long motorway run at constant revs??

She will run rough right up through the rev range, feels like its missing on 1 or more cylinders. She will still rev and drive though and its much more noticeable when stationary/idling. Oil pressure and temps remain perfect throughout.

Interestingly if you turn her off and restart her immediately the problem is gone and she drives off nice and smooth like there was never a problem.

The only other problem she has at the moment (and I mention it in case there is a link) - she has an oil leak that I believe is either coming from the front crank seal or possibly around the head - typical M104 fare! Losing about 1L every 1000 miles - she is wet around the front and on the bottom of the engine.

Any thoughts appreicated!!

 

[Lagerlout]

Not an expert on this model but first port of call, check the ground straps on the car. Engine to body, gearbox to body (if applicable).

 

[carat 3.6]

Possible coil pack failure, or the loom to them.

 

[BlackC55]

Loom is the first place I would look.

 

[a lex]

I have of course read about the loom problems on the S models, but being a phase 2 96 car I thought this had been solved by then??

Can you adivse what and where I should be looking for?

 

[grober]

Other possibility bearing in mind the oil leak might be the inlet camshaft advance mechanism is sticking but as Olly and Carat say try the HT coil packs/leads /extenders or associated LT loom first. You are looking for signs of overheating/ insulation breakdown/cracking- Sometimes if you run the car in the dark with the camcover plate off you will see sparking but its not a reliable test

 

[GP801]

A long list of possibles. Coil pack, HT leads, wiring loom, ECU. I had the same tale of woe with our E280 104 engine. Previous owner replaced the wiring loom. Problem came back. New HT leads and coil packs cured it for a time. Problem would return intermittently and coil packs were being changed more often than expected. Finally it got so bad it was virtually undriveable. Turned out the loom or coil packs had fried the ECU. Since having a new ECU its been perfect. The moral in this story is to get it sorted asap because if left it can lead to much more expensive problems. The ECU alone was £1400. Good luck.

 

[a lex]

Ill have a look at the plugs leads and coils - as I presume these are cheap enough and easy to sort myself.......

Much further than that and its probably curtains for the car - I only bought her as a winter beater and its not something im going to plough 1000s or even 100s in to, to be honest.

Next dry day we get and ill start poking around - no workshop manual or experience with the M104 should make it interesting enough however!

 

[grober]

THIS WILL HELP YOU WHAT TO EXPECT you will have to remove the cross engine air inlet pipe [sideways] to get the cam cover plate off torx or allen headed boltsPeachPartsWiki: W124 Engine Wiring Harness Replacement

 

[a lex]

Thanks all,

Im hoping its something as simple as HT leads, as they dont cost the earth.

Ill probably have to wait until Weds to get stuck in!

 

[kth286]

check the evap system is working.

The elctrical valve feeding the petrol tank fumes into the engine can seize open and allowing the engine to suck in the fumes when it should not be; with consequent engine surging etc.

The valve has MOT on top and is normally on inner wing (offside).

 

[a lex]

check the evap system is working.

The elctrical valve feeding the petrol tank fumes into the engine can seize open and allowing the engine to suck in the fumes when it should not be; with consequent engine surging etc.

The valve has MOT on top and is normally on inner wing (offside).

Hi

Thanks for the tip - what exactly would I be checking for?

 

[grober]

Hi

Thanks for the tip - what exactly would I be checking for?

Locate the valve- remove the pipe that leads from the manifold to the valve and block it off temporarily-- your problem should disappear -temporarily. That should test whether the evap system is the source of your problem.

 

[tippandy]

Hi there, the valve is on the nearside inner wing just behind the abs unit.It has mot stamped on top and will have two pipes attached.If working you should hear / feel it clicking every 30 seconds or so.

 

[Dave Lewis]

From my experience tracking down a similar problem with my '96 E280 M104, it could be any of the above suggestions, plus a few more. I'd recommend checking for fault codes with a blink tester to narrow it down a bit. You can make one for a few quid with bits from Maplins, here's a diagram, and the interpretations:

These are the Pin 8 (ECU) codes for the E280 and E320 M104:
1 No fault found
2 Engine Coolant temperature sensor
3 Intake air temperature sensor
4 Hot film mass air flow sensor
5 CTP switch
6 Not used
7 Not used
8 Idle speed control (ISC) system at upper or lower control stop or CC or EA indicates "limp
home" mode.
9 O2S 1 (before TWC) - voltage too high, circuit open or voltage implausible
10 O2S 2 (after TWC)voltage too high, circuit open or voltage implausible
11 O2S 1 heater (before TWC) - Current too high/low or short circuit.
12 O2S 2 heater (after TWC) - Current too high/low or short circuit.
13 O2S (Lambda) control system operating at rich or lean limit
14 Injector, cylinder 1
15 Injector, cylinder 2
16 Injector, cylinder 3
17 Injector, cylinder 4
18 Injector, cylinder 5
19 Injector, cylinder 6
20 Self-adaptation at idle speed or upper/lower partial load at rich or lean limit
21 Ignition output 3 or ignition coil for cylinder 1 and 6
22 Ignition output 1 or ignition coil for cylinder 2 and 5 (Engine 111, cylinder 1 and 4)
23 Ignition output 2 or ignition coil for cylinder 3 and 4 (Engine 111, cylinder 2 and 3)
24 CKP sensor or magnet for position sensor not recognized
25 CMP sensor not recognized or implausible
26 Not used
27 TN-signal (rpm signal ) - open or short to ground
28 VSS - open circuit
29 Not used
30 Fuel pump relay module - open or short circuit
31 Not used
32 Knock sensors 1 and /or 2
33 Maximum retard setting on at least one cylinder has been reached or the ignition angle
deviation between the individual cylinders is greater than 6 degrees crankshaft angle
34 Knock control-output switch in engine control module faulty Momentary fault in
self-adaptation closed throttle speed/partial load
35 Model 124,129 and 140 AIR pump switchover valve and/or electromagnetic AIR pump
clutch. Model 202 AIR pump switchover valve and/or AIR relay module
36 Purge control valve - open/short to ground or B+
37 Upshift delay switchover valve
38 Adjustable camshaft timing solenoid - open/short to ground or B+
39 Exhaust gas recirculation switchover valve - open/short to ground or B+
40 Transmission overload protection switch - open/short to ground or B+ or open or closed or
implausible
41 CAN communication from engine control module faulty
42 CAN communication from ASR, EA/CC/ISC module or diagnostic module (OBD II) faulty
43 Starter signal (circuit 50) not present
44 Not used
45 Fuel safety shut-off of electronic accelerator or cruise control active
46 Resonance intake manifold switchover valve - open/short to ground or B+
48 O2S 2 (after TWC) heating circuit relay module - open/short to ground or B+
49 Voltage supply at engine control module implausible/low volts
50 Engine control module faulty or not coded.45 Fuel safety shut-off of electronic accelerator or cruise control active
46 Resonance intake manifold switchover valve - open/short to ground or B+
48 O2S 2 (after TWC) heating circuit relay module - open/short to ground or B+
49 Voltage supply at engine control module implausible/low volts
50 Engine control module faulty or not coded.

 

[kth286]

Hi

Thanks for the tip - what exactly would I be checking for?

With engine fully up to temp, and idling, it should be pulsing about 2 beats per second.

You can both feel it and hear it ticking away when it is working.

 

[a lex]

UPDATE:

So, we took it around the UK over XMAS and did about 1400miles in it. The problem was still there, quite bad on some days and then the next driving 400miles without a hiccup.

I managed to squeeze in an appointment at Mer-Tech in Hull whilst on the way down to Dover and the STAR reader identified a mis-fire on cylinder 1 only.

With it being only 1 cylinder affected the Merc beards said we can rule out the coil as it supplies two cylinders (1&6), which makes sense.

They did a temporary replacement on the HT lead to cyl 1, but to no affect; with the same symptoms remaining - I still managed to drive her back to NL though without too much fuss.

This morning ive replaced all 6 spark plugs and put in a brand new HT lead to cyl 1. I will be replacing all 3 HT leads but cant do the rest until tomorrow due to a **** up at the stealer. For whatever reason replacing the plugs and 1 HT lead has actually made the problem worse

Its now got a constant misfire that doesnt disappear on the restart

A few questions :

- Could it possibly the coil even though its only affecting cyl 1

- The small rubber boot the sheaths the HT lead where it enters the coil is split lengthways. Could this be a cause?

- Any other ideas......? The beards at Mer-TEch did not suspect loom.

- I know its not the MAF as I have had the problem with the MAF disconnected.

- I cannot find the Evap valve! :S

Obviously the other 2 new HT leads may fix it tomorrow, but failing that im afraid the old girl has to go in the bin - a bit of a shame considering she passed the MOT last week.

 

[tippandy]

Its possible that the loom was quite fragile and in disturbing it while changing the plugs and lead it has made it worse.If you still have the bits you removed i would refit them to see if it puts the problem back to its original state.

 

[Dave Lewis]

If you're replacing the 3 plug leads, you should also replace the three connectors underneath each coil, that connect the coil direct to the sparkplug. These are a well known cause of misfires, they degrade with time. They should always be replaced with new ones whenever sparkplugs are changed, even if they look okay to the naked eye.

 

[a lex]

If you're replacing the 3 plug leads, you should also replace the three connectors underneath each coil, that connect the coil direct to the sparkplug. These are a well known cause of misfires, they degrade with time. They should always be replaced with new ones whenever sparkplugs are changed, even if they look okay to the naked eye.

Hi Dave,

Sounds sensible, but my problem is on cyl 1 which is not connected directly to the coil, but via a HT lead.

Just been playing with it again.

Started up fine, running smooth. Drove car slowly with gradual acceleration and all was OK. Then hammered it and braked quite sharply back down to idle - mis-fire appears.

Have jiggled/poked the loom both when its running smooth and mis-firing with no difference at all.

Have identified and checked EGR valve just now - makes no difference.