W123 230E 1982 misfiring

[Will]

The old pump wasnt seized. It was fitted only 2000 miles ago. It was simply changed because it was sometimes noisy and it was an easy replace just to rule it out. But the new pump is behaving exactly the same. I think it unlilkely that they could both fail the same way.

Pretty confident the relay is ok. The pump is running when the misfire occurs. Like I said the car can be driven gently and only misfires when more than a gentle throttle is applied. I will try bridging it to rule it out.

The airflow plate doesn't have a potentiometer. There is no ECU.

I’m thinking of slightly later M102 jetronic.

I’d still recommend ruling out the fuel pump relay though as a process of elimination - does it have the rev limiting function on your age of car?

 

[alabbasi]

I had a similar issue on an M104 engine which turned out to be the insulator that sits below the rotor which was damaged. Is it a consistent miss or something that happens under load? If it's a miss, you can pull the plug wire off to identify if it's coming from one particular cylinder. You only have four so it should be easy enough to check.

 

[grober]

Have you checked the distributor vacuum/mechanical advance when the engine is hot?

 

[bikeman]

Does it only misfire during driving or can the misfiring be replicated/provoked by throttle alone? If the latter, an in-line neon tester can be installed and observed. If its flashing falters....

It revs fine at a standstill.

 

[bikeman]

I’m thinking of slightly later M102 jetronic.

I’d still recommend ruling out the fuel pump relay though as a process of elimination - does it have the rev limiting function on your age of car?

If the FP relay was playing up I would get intermittent problems starting, stalling and random problems while driving. Since it only misfires during acceleration and the fuel pump never actually stops I'm ruling this out.

 

[bikeman]

I had a similar issue on an M104 engine which turned out to be the insulator that sits below the rotor which was damaged. Is it a consistent miss or something that happens under load? If it's a miss, you can pull the plug wire off to identify if it's coming from one particular cylinder. You only have four so it should be easy enough to check.

What insulator? Do you mean the spark arrest shield? It's fine, not cracked etc.

As outlined in OP the misfire only happens when accelerating after fully warmed up. No problem revving at a standstill.

 

[bikeman]

I've been wondering about the fuel damper. It's the only thing between the tank and the pump. How do they work? Could it be restricting fuel? How can I check it, Its a £150 item so I'm not just going to swop it?

Anyone?

 

[Will]

Anyone?

Is this the fuel accumulator? Sorry in advance if they are different on earlier vehicles, but I thought they were designed to maintain system pressure AFAIK. Can’t see how it would cause an intermittent issue whilst running only when the engine is warmed up myself.

Regarding the fuel pump relay, I only suggested bridging it to eliminate it considering how much you’ve already resolved. You referred to the issue as a ‘violent jerking misfire’, which seems to suggest a significant fuel or ignition issue?

It’s not clear from reading a few lines of text how bad this really is. I’ve had fuel pumps cut in and out with a faulty relay with a similar sounding description but I appreciate your comments relating to only doing this under load and you will be best placed to decide on the issue and course of action.

Good luck, I hope you get to the bottom of it

 

[grober]

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7Mins 30 onwards

 

[alabbasi]

What insulator? Do you mean the spark arrest shield? It's fine, not cracked etc.

As outlined in OP the misfire only happens when accelerating after fully warmed up. No problem revving at a standstill.

Yep that was the symptom I had. I'd also steer clear of Bremi for ignition components as they have proven to be sub standard

 

[optimusprime]

So you say, but i found Beru or Bosch the part , and nothing in the centre .

 

[optimusprime]

Will You can test the accumulator .First remove it .And then check if it holds vacuum .

 

[bikeman]

Will You can test the accumulator .First remove it .And then check if it holds vacuum .

Its not the fuel accumulator. It holds pressure. If it had failed it would affect hot starrting.

 

[bikeman]

Is this the fuel accumulator? Sorry in advance if they are different on earlier vehicles, but I thought they were designed to maintain system pressure AFAIK. Can’t see how it would cause an intermittent issue whilst running only when the engine is warmed up myself.

Regarding the fuel pump relay, I only suggested bridging it to eliminate it considering how much you’ve already resolved. You referred to the issue as a ‘violent jerking misfire’, which seems to suggest a significant fuel or ignition issue?

It’s not clear from reading a few lines of text how bad this really is. I’ve had fuel pumps cut in and out with a faulty relay with a similar sounding description but I appreciate your comments relating to only doing this under load and you will be best placed to decide on the issue and course of action.

Good luck, I hope you get to the bottom of it

Its the fuel damper not the accumulator.

The misfire is BAD. The car will barely accelerate. It's not intermittent. Once warm the car just wont accelerate but can be coaxed gently up to high speeds and will maintain speed until an incline. Then it will jerk violently if given any gas.

I dont see how an ignition problem could be so dependent upon the throttle. It would seem pretty unlikely that the relay would play up and then immediately work as soon as the gas is backed off. I would expect intermittent stalling, bad starting etc if there was an electrical fault. But I'm told the fump delivery and fuel pressures are ok.

I need to check out what the fuel pressure is doing under acceleration myself.

 

[bikeman]

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7Mins 30 onwards

Useful. Thanks. He says the fuel damper is a hollow chamber, so thats not going to be the problem

Maybe I should fit the old pump in series like he says at 13:00. A shame he's in the US.

 

[optimusprime]

Its not the fuel accumulator. It holds pressure. If it had failed it would affect hot starrting.

I did not say it was the accumulator ..my iinformation was,, how one can test the accumulator before purchasing another one wuilly nilly . And if it had failed it would affect both hot and cold starting .

 

[bikeman]

I did not say it was the accumulator ..my iinformation was,, how one can test the accumulator before purchasing another one wuilly nilly . And if it had failed it would affect both hot and cold starting .

I got that. Starting hot or cold is not a problem. The accumulator holds a vacuum.

 

[bikeman]

Interesting. I'm pretty sure I've checked that the ignition module isnt getting hot but I'll check again. I have done the measurements in the manual and they were all ok.

I've opened the ignition module and it all looks brand new in there, no damp, no overheating components at all. It also doesnt get hot when the cars is driven. I don't think it is the problem.

 

[optimusprime]

1 How did you resset valve clerances ? 2 What spaark plugs are in the engine ? I would back step and buy a new Bosh rotor arm then forget the HT side . As a rule i would not mention this ---- I have known ECU play havoc when the caps inside go bad . Easy to check them, just open the ecu up and inspect if they are split open on the tops. caps number are 220140 x 2 on top they are replacable ,. Then the ECU can be ruled out.

 

[bikeman]

1 How did you resset valve clerances ? 2 What spaark plugs are in the engine ? I would back step and buy a new Bosh rotor arm then forget the HT side . As a rule i would not mention this ---- View attachment 140692I have known ECU play havoc when the caps inside go bad . Easy to check them, just open the ecu up and inspect if they are split open on the tops. caps number are 220140 x 2 on top they are replacable ,. Then the ECU can be ruled out.

Did you see my post prior re the ignition module?

The HT side had been completely renewed with Bosch leads, plugs (H7DC), dist cap and rotor.

Dont understand your Q re valve clearances. I've done them many times and know what I am doing.