1991 124 230TE Automatic Gearbox Problems - Lack of Power

[Ade]

It never rains but it pours! I've just come back from holiday in the beastie and the auto box is being a bit naughty. I have complete lack of power when going up hills (being overtaken by a car towing a Caravan is a bit embarassing I can tell you) and the gear changing is a bit erractic to say the least.

I took the car to a specialist today who test drove the car who said that although the box itself was probably sound (yeah yeah 'till it's up on their ramp in bits) it is possible that a relay called the 'kickdown' relay is at fault as this was common with Mercs. I was told this relay controls the oil pressure in the box when the car is under load.

And there in lies the problem! Apparently this relay is usually mounted behind the battery next to a fuel cut off relay. However when looking for the relay, it weren't there! There was space for it but no relay or connections. The specialist called Mercedes who said there wasn't a relay listed for my year!

Anybody shed any light on this.

I'm told a a recon box is gonna cost about £1000 so I'll like to try the relay first if it exists! Alternatively anyone recommend a good gearbox specialist or somewhere cheaper in the South East? Preferably close to Dartford? Don't fancy the further embarrasment of being overtaken by too many pushbikes.

As an aside looking under the car at the holiday site I found the electric connection plug to the box everso slightly loose and the securing clip not in place. I closed the clip but it didn't make any difference . However, is it worth checking this connection?

 

[paulcallender]

The relay is a double relay shared with the fuel pump relay, so it must be there. Did you remove the black plastic panel behind the battery? It is behind the ECU which has a large connector on top of it, in between another ECU.

Are you sure its lack of kickdown that caused the poor performance? Surely, if you have no kickdown, you could simply get round this by using the gear lever into the "3" or "2" position?

 

[Ade]

Paul

I have kickdown. The problem is lack of power not the kickdown which appears to be 'out of synch' with what the box should be doing and I'm led to believe by the specialisit that this relay also controls line pressure in the box. Are you saying the fuel pump relay (I mistakingly referred to this as the fuel cut off relay)and kickdown relay are in the same black box?

Manually changing down to '2' or '3' makes no difference to lack of power.

Ade

 

[paulcallender]

The fuel pump relay and the kickdown relay are in the same black box, which is twice the size and has twice the number of pins as a regular relay.

In this case, I would suspect something other than the auto gearbox. I guess, for power loss issues, check things like compression on each cylinder, blown exhaust, ignition timing, etc. Also, are you achieving full throttle? Could be you need adjustment on the throttle cable.

 

[Ade]

Paul

Thanks for your reply.

The relay is about 70mm x 35mm x 60mm deep, is this larger than a 'regular' relay.

I understand what you are saying about the compression and timing etc but engine appears to be running fine. Throttle adjustment appears ok. I would say the power loss is almost definitely down to a transmission problem of some sort, whether internally in the box or in the control. I will check the relay to see if its operating ok but this is definitely one of those FUD moments.


Ade

 

[flyingtech55]

Hi Ade

I would also suggest that the problem lies with the engine rather than the autobox. Does your car have a rev counter on the dashboard. You can test the 'box selections are working by driving the car up a hill and then manually selecting the various gears. The revs should change up and down according to the gear selected.

The test we used to do was to chock the car and apply the brakes, put the car into first gear and floor the throttle. If everything was working correctly the engine revs were purposed to be about 2200. If they were only say 1400 there was stator slip in torque convertor, if 1600 or over but less than about 2000 then the power output of the engine was down and if over 2500 then it was clutch or brake band slip in the gearbox. This was the test for the autoboxes in BL cars. Please note though you mustn't do this test for more than 10 seconds because you will overheat the torque convertor and/or the brake bands if they are slipping. Obviously the engine has to be fully warmed up and check the engine oil and gearbox oil levels first. It used to be a handy way to at least get an idea of which area the fault lay; torque convertor, gearbox or engine. Different figures might apply to Mercs but I believe that generally these figures apply to most torque convertor type autoboxes because the makers adjust the size of the components according to the power output of the engine used.

The problem is that the torque convertor/gearbox combination will tend to compensate for and mask engine faults unlike a manual car where you get a much better idea of what the engine's doing.

Hope this helps

Gliderman

 

[Ade]

Gliderman

Thanks for the advice. Driving up and down hills and manually changing does change engine revs but whether within the recognised tolerances I'm not sure. Car seems fine going down hill!

Also I'm not sure if I could carry out the test you suggest but will give it some serious thought. Paul's and your suggestion on engine performance has got me thinking.

I have only just replaced the hydraulic valve lifters, which if I'm honest wasn't as successful as I'd hoped as 'tappet' rattle is still apparent occassionally (can of Wynn's to cure maybe?) Could these be keeping the valves slightly open and thus reducing compression? Can't see it personally but you never know.

Maybe a compression test is the answer to engine power loss but the engine, apart from what I've just mentioned, seems to be running fine. How much is a compression tester or how easy to hire one to check compression? Any ideas?

Any thoughts on fuel starvation? The reason being that in replacing the lifters, this was brought about by my noticing perished engine breather hoses under the air filter pan. One small hose branched off to some sort of diaphragm/pressure operated fuel control valve mounted next to the air intake aperture and this hose was completely severed. Replaced all the hoses but unsure what the valve actually does. Could this cause a problem? Replacing the hoses should improve the situation not worsen it surely?

The work I mention was carried out the evening before I went on holiday (last Thursday Week) so if it's not coincidence then I'm sure the answer lies here, although the reason I took off the air filter pan in the first place was to check for perished vaccuum pipes as the 'power loss'/gearbox problem was starting to raise it's ugly head but not as bad as it is now.

Any thoughts are appreciated

Ade

 

[paulcallender]

Hi Ade

Compression testers aren't expensive - for example Gunson (www.gunson.co.uk) do one for £16.80. So its worth a look. This would reveal valve, ring, head gasket problems.

Rather than fuel starvation, a leak in the vacuum side of things, could draw air in and interfere with the mixture, making it too lean and thus low on power. If its running lean, you may/may not see higher than expected engine temperatures. So, its a case of physically checking; I can't see any reason not to replace damaged hoses here.

The gearbox - this is the but where I'm unsure - shouldn't really reduce the power. There is a possibility, its one of these that temporarily reduces power whilst changing gear. And even if it did reduce power, I'm not sure how much by. If this is faulty, then it could be 'temporarily' reducing power, 'permanently'. Hopefully someone with good gearbox experience can help out here. But, I thought the 4 speed auto was a fairly straightforward one, the later 5 speed (auto) was the one with all the electronic gizmos.

Paul C
1990 230TE Auto

 

[Ade]

Hi Paul

From my experiences yesterday evening I think your thoughts are along the right track.

I removed the Fuel Pump/Kickdown relay last night to check for any obvious signs of failure and it looked fine from the outside with nice shiny contacts and no signs of overheating or damage on the outside. The relay felt nice and secure in its socket.

Unfortunately the relay is a sealed unit with no circuit diagram printed on the outside so without knowing what each terminal does I was unable to carry out even rudimentary tests.

I thought about replacing the relay on a 'try it and see basis' but the stealers inform me a new relay costs £126.68 + VAT so that wont be happening! Do you have any idea of diagnostic checks I could carry out to see if the relay is faulty or operating correctly, e.g. resistance measurements across terminals etc?

The bizzare conclusion to last night's tinkering is that after checking the relay and replacing it in the car I decided to go for a test drive for about 10 minutes. Although the performance was a little iffy it was no where near as bad as when I was on holiday or even when I drove it to the Auto Transmission specialist on Monday.

Although the test drive was not extensive I did run the Beast up a few of the steeper hills in the locality, the power wasn't far off what I would have expected and the gearbox changed up and down more or less as it should.

I didn't have time for an extensive run or the chance to belt down the motorway but I still felt the car wasn't going to hit top end speeds in the length of chosen road availabe, it still felt a bit limited and slightly sluggish on acceleration compared to normal.

I'm begining to feel that the gearbox hydraulics are probably sound as you have suggested. My gut feeling is the problem lies somewhere in the regulating/control circuit e.g. the aforementioned relay or a loose connection or the supply of fuel to the engine, which I assume works in conjunction with the gearbox control, and is creating the 'permanent' 'temporary' loss of power scenario you suggest.

Any further suggestions are welcome as this is driving me nuts.

 

[Brabus]

Re: 1991 124 230TE Automatic Gearbox Problems - Lack of Powe

Ade,

Ihave had a similar problem. The outcome was that I replaced the fuel pump and filter which solved the problem.

The reason being is that the auto kickdown and fule pump relay are the same and can cause problems.

It never rains but it pours! I've just come back from holiday in the beastie and the auto box is being a bit naughty. I have complete lack of power when going up hills (being overtaken by a car towing a Caravan is a bit embarassing I can tell you) and the gear changing is a bit erractic to say the least.

I took the car to a specialist today who test drove the car who said that although the box itself was probably sound (yeah yeah 'till it's up on their ramp in bits) it is possible that a relay called the 'kickdown' relay is at fault as this was common with Mercs. I was told this relay controls the oil pressure in the box when the car is under load.

And there in lies the problem! Apparently this relay is usually mounted behind the battery next to a fuel cut off relay. However when looking for the relay, it weren't there! There was space for it but no relay or connections. The specialist called Mercedes who said there wasn't a relay listed for my year!

Anybody shed any light on this.

I'm told a a recon box is gonna cost about £1000 so I'll like to try the relay first if it exists! Alternatively anyone recommend a good gearbox specialist or somewhere cheaper in the South East? Preferably close to Dartford? Don't fancy the further embarrasment of being overtaken by too many pushbikes.

As an aside looking under the car at the holiday site I found the electric connection plug to the box everso slightly loose and the securing clip not in place. I closed the clip but it didn't make any difference . However, is it worth checking this connection?

 

[Ade]

Brabus

Thanks for the input. With help from Paul C and Gliderman I'm beginning to suspect a fuel problem especially since I've 'reinstated' the fuel pressure regulator (refer previous post in this topic).

In changing the pump and filter what was the damage(£) and where'd you get the parts? Where are they located? I have a 'fuzzy' whine from the rear which has been there since I bought the car. A Dodgy pump which has finally called it a day?

Any idea how to test the pump?

Weird how these things can manifest themselves as looking like other bits are responsible.

 

[sebastianforbes]

hi there

it might not be relevant but......

the other night the front fogs on my '89 300te stoppped working. i thought for a while and then went to the fuse box. i pulled the fuse out, wiped it down, put it back in and gave it a wiggle. the fogs worked once more and then stopped, so i wiggled it some more and now the contacts must have cleaned up and improved their connections.

so what's the moral - well the cars are getting on a bit, so just give it a wiggle or two.........you never know.

cheers

sebastian.

 

[Ade]

Sebastian

I agree.

Have just Road tested the beast again, I think the next step is Brabus's suggestion. I don't know whether I'm being swayed because the idea is in my head but Fuel starvation is seemingly becoming more and more the likely cause

 

[G3maw]

Ade,
For what it's worth, I'd get the exhaust emission checked. Reason(s)?
1 - it will tell you instantly whether the the fuel/air ratio is right ( too much air and this will show if you have a weak mixture or not)
2 - get the garage to put the nozzle of the exhaust emission lance into the cooling header tank where it can 'sniff' for any oil content in the coolant ( this is a reliable test for any head gasket problems)
As well as being a good (and cheap) diagnostic check on the health of your engine, it also helps in the process of elimination needed to 'nail' faults such as yours. Most likely it will turn out to be something very simple like the fuel pump filter!
Best of luck.

 

[Brabus]

Ade,

Don;t know where you live, however if you want spares at agood price try www.dronsfields.co.uk they do mail order for new and used Merc parts. definitely sounds like a fuel pump problem. The whining noise is the the fuel pump struggling to supply fuel. Pump and filter are loacted at the off side rear by the fuel tank.

 

[Ade]

Brabus/G3maw

Thanks for that. I've bought the filter mail order through GSF (£16.50 all in).

Euro car parts want £75 odd for a new pump. I'll see how the filter affects the situation before I decide on the pump.

I'm going to check out Dronsfields as well.

 

[Ade]

OK

So I changed the fuel filter. Slight improvement but still the beast is playing up.

Next step - I've changed the dizzy cap (the old one had some serious tracking going on inside), rotor arm and plugs.

Result - Still no change. The old plugs look as if the mixture is actually on the rich rather than lean side.

Car still sluggish on acceleration, slightly odd gear changing and can't pull more than 70mph on the motorway. Still finding inclines more than a fagbox high a struggle.

Before I start spending serious money does anyone any other ideas on what to check?

I think a visit to the stealers for a diagnostic check is looming, Gulp!

Please God, don't let it be the box................

 

[mike65]

This maybe completely off-the-wall-wrong but is'nt there a vacume feed off the throttle body (just behind the air intake) which feeds through to the autobox in some way? If that not connected might that account for bad shifting?

Mike.

 

[Ade]

Mike

Any suggestions are welcomed! I've looked for any missing/broken pipes and, apart from those already mentioned, can see nothing obvious. Not to say it isn't there mind you!

Ade

 

[G3maw]

Ade,
From your info. about the colour of the plugs, it sounds as though the HT supply from the coil might be suspect. Try and have a look in the engine bay around the top of the coil,with the engine running, IN THE DARK! If there is a 'leakage' of sparks here then you might be able to see it. The other possibility might be an internal breakdown of the isulation within the coil itself causing a reduction in HT output. It sounds as if your 'gearbox problem' is a symptom of reduced engine power ie. continual hunting for ratios, rather than the main fault. If you need to seek further advice/diagnosis try to locate an independent garage in your area who are familiar with the K Jetronic system. Don't give up!