Ok, this is a bit of a long story so please bear with me.

I picked this up for $500AU not going. Its now a daily driver but still has some issues I need to sort out.
The engine is the M104 IL6 3.2L engine with HFM injection and VDO ECU as found in 90's E320 et al. The engine and power train in these cars are 100% Mercedes Benz and not 'license built' copies, they are genuine Benz right down to the part numbers so I use MB parts if I buy new stuff (partly because the only Ssangyong dealer in the state is next to useless for parts.)

The original 'not going' problem was due to the infamous OVP relay having internal dry solder joints. I repaired these and the vehicle started immediately. 1st win. Windscreen wipers didn't work, was about to replace the motor when a fellow Musso owner suggested that if it had been standing a while (it had) good chance the linkages in the air intake box under the windscreen were seized. Drowned them in WD40 and they started to work. 2nd Win. There were a few minor issues with door switches, interior front light switches etc that responded well to WD40 and patience.

Prior to my getting it, it had dropped the timing chain and had the head rebuilt by a Mercedes mechanic, new valves, chain, guides, cam sensor etc. Aside from one slightly noisy hydraulic lifter, the engine is mechanically excellent, not a trace of smoke and uses virtually no oil.

Otherwise, mechanically it seems fine (though the front CV joints are getting clicky and will need replacing) and the brake pad warning light is on so need to do them soon too. It's done around 215,000km so far, about 2000 of those since we got it. Trans seems fine, no leaks, no overheating etc. Shifts are a bit rough when the engine is missing or otherwise misbehaving, but smooth when its running well (when cold in other words) AC works good, interior is good and all the lights, bells and whistles etc seem to work fine.

Now to the existing issues.

Problem 1. Missing. Seems to be an 'under load' thing. Back off the throttle a bit sometimes and it will run evenly again. I have changed coil packs which seemed to improve it, but it's still doing it. Once you get to cruise speed it seems to settle and not miss, even at fairly high speed, load it up by putting your foot down and it will usually start missing until you back off the throttle.

Problem 2. Won't increase power from idle, particularly under load. This can make it 'interesting' to drive as you try to take off from an intersection and it will barely increase the revs from idle, so you find yourself idling across an intersection with traffic bearing down on you... You can hear the change in intake sound from the throttle butterfly opening, but no increase in power. As it very slowly picks up, it will get to around 1500/2000 rpm and then it will pick up more or less normally.

Problem 3. Cam sensor error from read of computer. The original sensor was smashed when the cam chain let go. It was replaced with a new one at the time, however the computer says it's not there. I've measured 2mv pulses that look right at the computer and the sensor was again changed with one from a working Musso M104 with no change to the outcome. I have checked the spacing from the cam shaft tooth and it's within the specified .5mm. I fully expected changing the ECU to fix this problem but it made no difference, so I suspect it's a problem in the cable somewhere. The Musso doesn't seem to have the 90's wiring harness degradation issue - not sure why, but suspect the harness might be Korean rather than Mercedes made, but not sure, regardless all the wiring looks good.

The first two problems are not present when the engine is dead cold. It doesn't miss and the it accelerates from idle normally. After about 5-10 minutes running the problems appear.

So far, I have replaced the following components trying to sort this:
1. Cam Sensor (Twice)
2. Throttle body. (replacement used but had around 99,000km on it)
3. Coil Packs. (Used but supposedly good from a working engine)
4. ECU (Used but supposedly good from a working engine)
5. HFAM Sensor New aftermarket unit put on before I got it - but after reading about issues with non Bosch ones, replaced it with the original, which appeared only to need cleaning. Did that and it seems fine. Computer says it's ok so it's in the vehicle for now. Disconnecting the HFAM does not alter the miss/no acceleration issue one way or the other.

5. Crank sensor (unrelated to the stated problems, engine stopped and refused to start after a week or two of intermittent 'sudden deaths', which I suspect were an intermittent fault in the sensor. Replaced with new, no further issues in that area. Car starts almost instantly regardless of temperature.

I am now considering fuel injectors. These have been replaced prior to my buying the car, not sure when, but they appear to be used. I only know they were changed because the old ones were in a box in the back.
I changed the throttle body thinking that the throttle position sensor might have been crook. It did seem to improve it a little, so perhaps it was on the way out, but I'm pretty sure the sensor in the replacement is fine, as I said, when it's all dead cold, it runs fine.

I am going to change coil packs with brand new ones on general principles but I don't think they are the problem to be honest, so I will try injectors first.

Aside from the cam sensor fault, the computer is not showing any fault codes. Clearing it still sees the cam fault come back after one run of the engine.
I'm going to try running a length of RG58 from the sensor to the ECU and replacing the existing coax that goes to pin 8 and pin 19 on plug 2 of the VDO ECU.

I am using a clone Vag-Com USB cable, appropriate adapter to the 14 pin round plug on the Musso and HFMSCAN on a laptop to read and clear error codes.

I've considered sending the old throttle body and ECU away to have them rebuilt just to be certain, but there is no one in this country that seems to do that. I've messaged a couple in Europe, but they don't seem interested.

So, my questions are:
1. Any ideas about any of these faults?
2. Any ideas about somewhere I could get throttle body or ECU rebuilt?

ECU is standard as fitted to E320 et al. Marked '3.2l 6 Zyl' Numbers below from HFMSCAN.

System: HFM
Manufactured: VDO
Ident: M0 32853 VR0
ECU Nr: 162 545 30 32
Hardware date: 00/00
Software date: 04/97
Diagnosis index: 45/01

Any ideas or hints very much appreciated. I've never owned or worked on a Merc system before - so I'm learning as I go. I really like the car and thinking our next vehicle will be MB all the way - local mechanics seem to hate them with a passion (which I find hard to understand as they seem to be pretty straight forward once you understand how they work) and there is no local MB dealership anyway (nearest is 225km) so need to sort it myself really.



Regards

Geoff
Port Pirie
South Australia

you need the cam sensor signal to make the engine run smooth, otherwise you will face a dead stall type situation before power is applied.

This is because the ecu doesnt know when the engine is at true TDC,

get that sorted and Im sure you will see lots of improvement,

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

This is normal for a hydraulic shift trans. When the engine has low power, manifold vacuum is low / throttle is opened farther. This leads to higher line pressures / later / harder shifts as the trans thinks the engine is under load but isn't.

This is generally ignition related, at higher engine loads voltage required to jump the gap increases. This can lead to not establishing a spark / spark leaking out through a boot or coil. Once engine load is reduced, the spark returns to the plug tip.

Coil or boot failure is pretty common.

Have you checked fuel pressure driving under load?

I'd hang a volt meter / scope on the throttle position sensor output to see if the throttle is opening enough. MB of this era had ASR ( Acceleration Slip Regulation ) tied into the ABS system. Perhaps the ASR is turning on due to a erratic rear wheel speed sensor. On a MB this can be completly shut off for dyno testing.

2 MV sounds low, measure it at the sensor and see if that matches the computer end.

I'll counter the previous suggestion that the cam sensor causing the run problems. Cam sensors are to sync up the injector pulses for a slightly smoother idle. Once the engine gets up in revs, the injectors are open longer making the sync not an issue. This engine has waste spark where 2 plugs are fired from the same coil making any sort of compression / exhaust stroke ignition sync a non issue.

For engines in general, the cam sensor is only looked at during cranking in order to syc things up so a come and go sensor won't be an issue.

Ok, thanks. Makes sense. I'm not exactly sure which particular trans is in this vehicle, being full time 4WD. There is a TCU under the left front seat, though I've no idea if that can be interrogated separately, at least not with HFMSCAN. The (former) Merc mechanic that rebuilt the head told me he'd looked at the trans and it seemed fine. He's been very helpful actually, he was able to tell me exactly what had and hadn't been done and a lot about the overall condition of the engine even the owner didn't know.


Yeah, that was my thought too. I have replaced all three coil packs (admittedly with s/h) and one boot that was definitely dodgy. It feels like weak spark to me as well.

Yes, I thought the coil packs would fix it. Might just change the entire ignition system (coils, HT leads and coil boot to plug). Plugs are brand new and seem to be fine.

No, no means to do so. It will cruise happily at high speed (120kmh plus) so I don't really think that's it, but I'll see if I can find someone with a fuel pressure gauge - any idea what size the fitting is?

The throttle is physically opening, you can hear the intake note alter when you hit it - wondering about the Throttle Sensor again so might try that. It is a s/h part but only had 99,000k on it. The car had 213k when I got it.

This model Musso doesn't appear to have ASR - the throttle body appears to be a non ASR type.

Seems to be about the same, it's what it's supposed to be according to a diagram I found somewhere of the waveform. I used an oscilloscope to look at it. It's a reluctor type passive sensor not a Hall Effect one.

Ok, as far as I knew the cam sensor was only there so the ECU could adjust the intake valve timing, there's a solenoid on the input camshaft to do this. The crank sensor supplies the TDC and without it, no spark. I'd mentally put the Cam Sensor issue on the back burner while chasing the missing/poor acceleration because I didn't think it would be that significant. My initial thought after seeing that there was a signal at Pin 8 on the ECU was that because it was so low (2mv is not a lot of signal but it seems to be what it's supposed to be) there was probably an opamp or possibly a Schmitt Trigger on the input to make the pulse a bit easier for the computer to handle and it had packed up. I was quite surprised when a replacement computer didn't fix anything, as I had assumed after changing coil packs that a (common) issue with the ECU driver transistors for the coils was the problem and fully expected that to fix it.

Well, that's not my understanding with this engine, the tech articles are quite specific that the ECU controls the input valve timing (over a limited range) using the difference between TDC (from the crank sensor) and the camshaft position in real time from the Camshaft sensor. That said, if I hadn't been able to get the data from the ECU I'd never have looked at it as it had been replaced when the head was rebuilt after the timing chain failed. There was also an issue with the Cam Solenoid, but this was due to an internal short in the plug, I simply attached the leads on their own by taking the plug apart and that error code went away and never returned.

Thanks for your help with this.

Regards

Geoff

I will look into that further, however my understanding is that the ECU determines TDC from the crank sensor, and that the camshaft sensor is purely for the ECU to know where the camshaft is as it varies the intake valve timing via a solenoid on the end of the camshaft. The engine doesn't usually stall, it simply refuses to increase power or revs, it can be so bad it won't climb the camber of the road without several attempts, this can be very frustrating when turning onto a main road from a side street for instance and you have to back up and let traffic go because the darn thing won't accelerate.

Regards

Geoff

You are correct on the vvt part of it.

The cam sensor reports to the ECU the actual cam position, the ECU then has confirmation that the cam has advanced.

the cam sensors main function actually is to time the injector sequence so the engine can run one injector at a time rather than batch or group (like starting).

This same stumble happens in other cars too if the cam position signal is missing. There will be spark and fuel but not at the precise moment as the ecu has 1 in 6 chances to time the firing correctly for a 6 cyl engine, If the engine is ancient group or batch fire you will see no change (there would usually be no cam sensor in those either - like ancient GM or toyota/daihatsu)

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

There are some subtleties between these two posts:

Yes, this is so the ECM knows to trigger a no cam advance trouble code.


For this to be true, the cam magnet would need to see a PWM input to modulate the oil valve. I'm not so sure this is the case since oil pressure isn't well regulated and the PWM dwell would constantly be trying to catch up making for a surge.

I don't think there is any benefit to a partly advanced cam over on / off anyway and I don't recall seeing a " cam advance X degrees "data value when wing a Star on my 97 SL or C280 ( this has ME 2.0 / 2.1 )

Hang a scope on the cam magnet input and have a look. ( or for a more portable way, a volt meter )

Ok, not quite sure I'm following this. Is there supposed to be a magnet on the lug on the camshaft that the cam sensor 'sees'? There isn't. AFAIK it's just a bit of metal that induces a slight voltage (around 2mv as near as I can tell) in the sensor (which is much the same as the crank sensor, it's just a winding of wire on a core) so it generates a pulse, I don't see any evidence of modulation - pulse width or otherwise, though I suppose the pulse width would be shorter at high speed and lower at idle. I'm not sure exactly how it works, but I'm not following the oil bit, there's a solenoid device at the end of the camshaft that is driven by the ECU which (somehow) adjusts the camshaft and thus the valve timing, AFAIK, it's on or off, not a variable thing, but I could be wrong.

One bit of good news. The missing has been fixed. It seems there was a pinhole in a plug lead boot I missed. I went through all the leads and boots again today and found it. Hard to miss with a big white patch of oxidation all around it. Can't get leads here so I have used a 'conventional' silicone plug lead from a Nissan, pushed it on the plug, then peeled off the damaged rubber boot over the plug end of the original lead and put the distributor end and it's boot into the connector that used to go to the plug with the Nissan distributor type boot over the top to stop it flashing over. Works perfectly. I'll get a new set of plug leads, but for some stupid reason a set of 3 appears to be something like $200 which is ridiculous even for Mercedes Benz I think. But it's smooth as silk now, the issue with the failure to rev up from idle remains, although it's not quite as bad now because at least it's running on 6 instead of 5. I suspect this is either injectors or possibly low fuel pressure. Can anyone say what the fuel pressure in the injector rail should be? There is some known issue with o rings in a surge tank on Musso's but not sure if that's associated with this problem or not - have to look into it further - but aside from injectors about the only other thing would be the fuel pump not delivering enough pressure, not sure if that happens - my experience with fuel pumps is that they work or don't, but it's my first Mercedes engine so... I did notice one injector has a small fuel weep where it goes into the rail, so I'll need to attend to that as well. That's a recent thing, but it does suggest they were either not new injectors (look used to me) when they were replaced or they didn't use new O rings (probably that too). What's a set of injectors and O rings worth these days? Is it worth getting them rebuilt? I CAN get a set of rebuilt/reconditioned injectors from Ebay for $220AU which seems like a good price, any experience with recond v new injectors out there please?

Regards

Geoff

Geoff in Oz