Backfire in cat on kickdown

[strelitzia]

I've got a problem with my '97 W210. If i'm driving at about half throttle, when i give it a bit more accelaration i get a backfire inside the cat and a hesitation before the car will pick up. I've also noticed that the car is very sluggish when cold.

I've also noticed that the autobox seems very reluctant to change down when climbing long hills, and once it has changed down, it will wait until it is almost redlining before it will change back up.

I don't know if they are related problems, or two seperate issues.
Car has done 180,000 with full history by MB up to 170,000. I don't know if it has ever had an oil change on the box, and i can't be sure that the oil level is correct as they don't have a dipstick, which seems crazy.

Any suggestions on what my problems may be?

Thanks
Steve

 

[television]

I've got a problem with my '97 W210. If i'm driving at about half throttle, when i give it a bit more accelaration i get a backfire inside the cat and a hesitation before the car will pick up. I've also noticed that the car is very sluggish when cold.

I've also noticed that the autobox seems very reluctant to change down when climbing long hills, and once it has changed down, it will wait until it is almost redlining before it will change back up.

I don't know if they are related problems, or two seperate issues.
Car has done 180,000 with full history by MB up to 170,000. I don't know if it has ever had an oil change on the box, and i can't be sure that the oil level is correct as they don't have a dipstick, which seems crazy.

Any suggestions on what my problems may be?

Thanks
Steve

Your fault is fuel starvation or running too weak, the MAF sensor or the O2 sensor could do this.
When the car is under powered the box cant react in the correct manner, I would change the MAF first.

 

[strelitzia]

Your fault is fuel starvation or running too weak, the MAF sensor or the O2 sensor could do this.
When the car is under powered the box cant react in the correct manner, I would change the MAF first.

Emmisions were ok at MOT last month. If 02 sensor were faulty, then i would have thought emmisions would have been incorrect. I may be wrong as i'm no expert on emmision controls.

Worth cleaning the MAF? or just replace it.

Thanks
Steve

 

[NW_Merc]

Spark plugs? I had this on mine and a spark plug was fitted wrongly

 

[television]

Emmisions were ok at MOT last month. If 02 sensor were faulty, then i would have thought emmisions would have been incorrect. I may be wrong as i'm no expert on emmision controls.

Worth cleaning the MAF? or just replace it.

Thanks
Steve

It would pass ok if running too weak, its when its over fueled that it would fail.

If you take the O2 sensor if it was contaminated it would think that the fuel was too rich and weaken the mixture , this would normally put the check engine light on. I would unplug the MAF to see if there is any change.

 

[grober]

I would try to rectify this fairly quickly before it wrecks the cat. Any link to the fuel contamination problem of a couple of months back?? http://mbclub.co.uk/forums/showthread.php?t=34589&highlight=contaminated+fuel
I would be inclined to try cleaning the MAFF with the correct solvent first- plenty of posts how to do this --if that improves things temporarily----its a good indicator of where the problem is ---then change the sensor bit ( NOT THE WHOLE UNIT)- An insert is not too expensive from ECP. Contamination of the lambda sensor is more problematic unless you have the test equipment, since although gross contamination may be obvious, its difficult to tell from visual inspection a partialy poisoned one. If you have wrestled to get it/them out ( there might even be 2 --pre and post cat not sure ??)- a special spanner helps, its probably best to replace it/them anyway.

edit best to know what type of engine has it got ??

 

[strelitzia]

Any link to the fuel contamination problem of a couple of months back?? http://mbclub.co.uk/forums/showthread.php?t=34589&highlight=contaminated+fuel

Since i've owned the car it has only had BP ultimate in it, so i doubt if it's a fuel contamination issue.

An insert is not too expensive from ECP.

Do you have contact details for them?

Engine is 2.3 4 pot.

Did notice something on cold start this morning that may also be related to the problem. When i first started the car, there was a fairly load buzzing type noise from under the bonnet, (possibly a motor running??) which lasted for a minute or so. As soon as the noise stopped, the idle slowed down and became quite erratic until it had warmed up.

Thanks
Steve

 

[strelitzia]

I would unplug the MAF to see if there is any change.

Change??? Sure did change...it ran like a bag of nails. Flat spots, sluggish, 1200 rpm idle speed.

Is that what you would expect?

Thanks
Steve

 

[rajinder_1]

Since i've owned the car it has only had BP ultimate in it, so i doubt if it's a fuel contamination issue.

Do you have contact details for them?

Engine is 2.3 4 pot.

Did notice something on cold start this morning that may also be related to the problem. When i first started the car, there was a fairly load buzzing type noise from under the bonnet, (possibly a motor running??) which lasted for a minute or so. As soon as the noise stopped, the idle slowed down and became quite erratic until it had warmed up.

Thanks
Steve

Bp fuel is good, but i had contamination problems in my sl320, they were refueling and the gunk ended up in my tank, long stroy short i dont use them as they refused that it was their fault.
As for you buzzing that the secondary Air injector more than likely it usually kicks in then goes off.
have you changed your fuel filter too????

Raj

 

[strelitzia]

I havn't replaced the fuel filter since i got the car 10k ago, but it had full history up to that point, so i would expect it to have been replaced at some time as part of a service.

I'm wondering if this is more of a gearbox issue than engine, as it runs fine in all other respects. The problem seems more that the box is unwilling to change down when the accelerator is pressed hard. If i were travelling at 50 with light throttle, then push the accelerator quite hard, but not to kickdown, the box will only drop one gear, and acceleration is still sluggish. I can move the stick to force it to go into third and it will pick up after a brief hesitation. If i use kickdown though, the box waits a long time before it drops through the gears, as much as 10 seconds, this is when i get the pop in the cat as the engine is obviously on full throttle and the fuel system has increased the fuel delivery to allow for the wide throttle opening, but it can't pick up the rpm to match as the gear is wrong.

What do you think??

Regards
Steve

 

[KLP 92]

Change the MAF sensor, it can be responsible for all your problems.

 

[television]

The Maf has to be the problem, the engine is running too weak, if it was too strong it would be smokey and thirsty

 

[strelitzia]

Ok, i've fitted a new mass air flow sensor from Euro Car Parts. Same Bosch part No. so i know it's the correct one. Car is still the same. Didn't notice any difference whatsoever with the new MAF sensor. Guess that was a waste of money

Any other ideas?

 

[Dieselman]

This could be a weak spark which will show up under load. Buy a cheap flash tester and check the output at each plug cap.
After that check the lambda sensor and for air leaks.

What is happening is that uncombusted fuel is passing into the cat, this can only be a result of grossly over rich mixture, too lean a mixture (but that normally gives spitting back), or not a good enough spark.

 

[Wully]

I had very similar problems on my C180 and it turned out to be a combination of coil packs and leads, to be honest i am sure the leads were the problem all along.

I don't know how many times i changed plugs and then disconnected the battery for around a hour and it seemed to clear then come back. My conclusion on that was the leads were being moved and making some sort of decent contact and then with movement returning to the same old problem.

May be worth checking?

 

[Dieselman]

I had very similar problems on my C180 and it turned out to be a combination of coil packs and leads, to be honest i am sure the leads were the problem all along.

I don't know how many times i changed plugs and then disconnected the battery for around a hour and it seemed to clear then come back. My conclusion on that was the leads were being moved and making some sort of decent contact and then with movement returning to the same old problem.

May be worth checking?

It's because the insulation breaks down due to heat when being used..This will affect the coils more than the leads.

 

[strelitzia]

Ok, tried new plugs, leads and also a fuel filter. No difference. Seems to be getting worse when cold. Extremely slugish now to the point i thought it was going to die on me today.

 

[Dieselman]

Get the Lamda output read, that should tell the state of the mixture strength.

What colour are the spark plug electrodes? They should be a light brown, black indicates too strong a mixture, white is too lean.

 

[rajinder_1]

just a thought, you could have a dodgy maf????? have u disconnected it and tried? or ask euros for a replacemnet...

its happened before on here..

Raj

 

[strelitzia]

have u disconnected it and tried?

Already replaced the Maf Raj. Why do people say to try and disconnect it to see if it's any different?

If it's disconnected it runs like a bag of nails. Lumpy, lack of power, poor idle

Just wondering what you would expect it to do with a disconnected MAF