190E 2.6 poor starting + lack of power

[chrisd87]

Hi everyone,

Ever since I've had my '92 190E 2.6 it's had a bit of an annoying problem (or set of problems), which now seems to be getting worse.

Firstly, it never tends to start very easily. It always does go, but often has to churn for a bit longer than you'd expect, particularly when cold. When the engine does start, it's always quite rough for the first few seconds. There isn't a problem starting when warm, although sometimes you have to release the key first, then it'll fire. Length of time from when it was last used doesn't seem to dictate how long it takes to start, either. It also never seems to fully go up to the high idle speed - even when cold it idles at about 750rpm. The battery is only about 6 months old, so I wouldn't have thought it'd be the culprit.

Secondly, and more importantly, the car often lacks power and has an uneven throttle response. Sometimes you'll try to accelerate and it'll pull crisply and instantly, but more usually it'll hesitate and seems as if there's a flat spot. It seems to happen when the engine's hot and cold. It feels like there's either some sort of fuel blockage, or the acceleration enrichment isn't working. The problem only seems to happen at lowish revs - once you've broken through the flat spot, it pulls ok.

Aside from this problem, when warm the idle speed always seems quite low (about 550rpm on the gauge), and is not 100% smooth and stable. It's not hunting, and the variations aren't visible on the tacho, but you can just hear it and the oil pressure rises/falls slightly at the same time.

So far I've tried replacing the fuel filter, and run some injector cleaner through it, but it doesn't seem to have made any difference. As I mentioned on another post on this forum, the EZL unit fitted when I bought the car was the wrong one (for a 1.8), so I've changed that for a (more) correct one (from a W124 300E, which seems to have almost exactly the same spec as the 190E 2.6 unit). I also replaced the plugs and air filter at the same time - neither were in a very good state.

I was wondering if this might be down to failure (or intermittent failure) of the OVP? I've never had any of the dash lights come on, and the ABS seems to be working. I wonder if there's any way to test the relay, as I'd rather not buy a new one for £75 if that's not the problem. If it's not the OVP, does anyone have any ideas?

Many thanks for any suggestions.

 

[chrisd87]

I'll add the following:
- The air flow sensor plate seems to move smoothly
- The car has never stalled

 

[neilrr]

As I mentioned on another post on this forum, the EZL unit fitted when I bought the car was the wrong one (for a 1.8), so I've changed that for a (more) correct one (from a W124 300E, which seems to have almost exactly the same spec as the 190E 2.6 unit).

I'd start there & find the right one.

 

[John Jones Jr]

Really by rights I'd have someone inspect the operation of the KE injection first rather than just changing parts as there's several aspects to an incorrectly functioning injection system like, idle control valve, cold start injector, throttle potentiometer etc, etc. Have you had the emissions checked? If the fuel mixture needs adjusting it will change the idle speed.
You can inspect the OVP joints & solder them if required, but I doubt this is the problem judging by your post. You may also have several faults too. Bad injectors, few change them. The coil could be on the way out, saw that before on my own 300E and it was intermittent fault too. Bad plug leads too could be an issue also. I realise I've not given you much assistance but do check distributor cap & rotor first.

 

[John Jones Jr]

Judging from the info I have at hand the correct EZL unit for your engine is 015 545 08 28, that's for car fitted with a cat which I presume your car has.

 

[chrisd87]

Thanks for the replies.

The car does indeed have a cat. It's a K-reg so I presume it went through a cat test at the MOT in May.

I realise that the EZL isn't ideal. The reason I went with the one I have is that I couldn't find a non-USA 190E 2.6 one for sale at a reasonable price. The one I've installed (008 545 62 32) has timing of 6-11° BTDC at idle, as opposed to the 7-11° of the original, and 27-31° at 3200rpm as opposed to 25-29° (without vacuum). With vacuum both are 40-44°. Obviously I don't know whether the curve is any different between the two. I have just come across this though, which suggests that I've got the trimmer plug in the wrong position. The Haynes manual suggests that '3' is the correct setting for unleaded fuel (which is where mine is), whereas it appears that only applies to non-cat vehicles, with 'S' being the position I actually want. I'll see if that makes any difference and keep a lookout for a spot-on EZL in the meantime.

Do you think it would be a good idea to test all of the fuel injection system sensors before proceeding?

There is an invoice for the replacement of the plug leads and dizzy cap in December 2012 (before I bought the car). Judging by the price, they weren't genuine MB or Bosch items. No mention of the rotor arm, though, so I'll take a look.

 

[John Jones Jr]

Well, I wouldn't imagine that the EZL unit you currently fitted is going have much of an negative affect on how the engine performs. As for the trimming plug, I can't comment but the 'S' setting does ring a bell.

Check the cap & rotor anyway, it's good preventive maintenance if nothing else. You can check the operation of both the idle control valve & cold start injector, simply by removing both and running 12V to them. Clean out the idle control valve too, I've used carb cleaner before with success. Also, check the operation of the idle micro switch mounted at the end of the throttle cable, sometimes they fail.

P.s. Dismiss the part number I gave you in my last post because now I've come up: 008 545 61 32, but I'm using a very dated info so, best to check it out yourself.

 

[chrisd87]

Thanks for that. The list of EZLs I've been referring to is here. Admittedly it's for 6cyl w124s, but my engine code is there in the first table (103.942), along with the unit you mentioned. The EZL I'm currently using is in the lower table, for engines with the codes 103.981, 983 and 985.

I'll get the multimeter out and have a look at some of the sensors. I'm just really puzzled as to why it sometimes performs so well, and yet at other times it's pretty hopeless.

 

[John Jones Jr]

I'm just really puzzled as to why it sometimes performs so well, and yet at other times it's pretty hopeless.

Check the engine wiring loom and the connectors. They can go brittle over time from heat & age. First move/shake the loom while the engine is idling and see if you can hear a difference in idle speed, if you can that's the problem or part of the problem. I presuming that you have checked the vacuum pipes and sundry hoses.

Let's know how you progress.

 

[balge]

OVP function test here -

OVP - basic function and test - Benzworld.org - Mercedes-Benz Discussion Forum

hth

 

[chrisd87]

Thanks for the further replies. I'll test the OVP just to be sure it's not at fault. I did wonder if the wiring might be dodgy - if there's a loose connection somewhere it might explain the intermittent nature of the fault.

Interestingly I took the car out tonight with the ignition timing trimmer in position 'S' as opposed to '3'. It definitely felt a little more responsive, although it did hesitate a few times so it hasn't solved the problem.

 

[martyz]

If you are not getting dash lamps on,check the single wire from the alternator to the connection block (black plastic) in front of servo,had to change it on mine as it had rotted,took a long time to suss but when I changed it all dash lamps illuminated.

 

[stwat]

Wunderpartz on eBay sell new OVP's for under £40. I would recommend buying one as the original will be well past it's sell by date by now. After many years of heat cycles the solder joints dry out and crack. They can be re soldered but they never last that long after the fix. For £40 you get peace of mind and another 25 year's of service from it.

I replaced the one in my 300SE and it cured all sorts of running problems.

 

[John Jones Jr]

Chrisd87, I also meant to say consider buying a book called:

'Bosch Fuel Injection & Engine Management' by Bentley Publishers ISBN O-8376-0300-5.

Always worth having imo even if some of it goes over by head and adds a bit of confusion. At the end of the day it will still give you a better understanding of what's what and it's worth it just for the Trouble Shooting section alone.