9 replies to this topic

[mrducati]

After I welded my broken exhaust, my 1998 MPi has been running incredibly rough and is very low on power. It is also very noisy! I must have broken the exhaust manifold gasket for it to be so noisy. Now is there a possibility this alone can make my car so rough and gutless? I know I might have pinched the lambdasensor wireing. Could this cause it to run so rough? Or have I fried my ECU? Or has some of the fittings on the injectionsystem turned bad? I have tried to wiggle all the connections, but I can't find an obvious cause. What is likely?

Edited by mrducati, 20 August 2014 - 12:10 AM.

[The Matt]

I'd fix the exhaust blow first, but yes, it's possible that you've fried the ecu.

[Captain Mainwaring]

Very possible - the earth path back is tortuous and the lambda sensor would break down easily

You could be lucky and have just taken out the lambda

Edited by Captain Mainwaring, 20 August 2014 - 02:50 AM.

[Ruckus]

You did disconnect and remove your ECU before welded didn't you? 

 

 

http://www.theminifo...-an-spi-mpicar/

Edited by Ruckus, 20 August 2014 - 10:53 AM.

[mrducati]

I'd fix the exhaust blow first, but yes, it's possible that you've fried the ecu.

I will do just that, and see how it works afterwards.

 

You did disconnect and remove your ECU before welded didn't you? 

 

 

http://www.theminifo...-an-spi-mpicar/

I forgot to do this unfortuantely.

[Ruckus]

Not good then...

[FlyingScot]

If it was just the lambda sensor the car would still run but incorrectly fuelled.
Sounds like something more troublesome I'm afraid.
The MEMS ECU is tough but spiking it with a welding current isn't good (especially via the lambda as it expecting an input).
Check and repair the obvious issue with the exhaust first and see where you are.

FS

[MiniAida]

I'd check all the vacuum pipework & also see what happens with Lambda sensor completely disconnected (do this whilst running to see if there's a difference connected / disconnected).

 

I think you may have got away with not frying the ECU as it works. It's unlikely that you would have caused it to slightly malfunction, more likely to not function at all if damaged.

 

If you think the gasket might be damaged, the inlet could be leaking air, so making the mix weaker.

 

Exhaust shouldn't affect it that much unless a pipe is blocked or air flow around sensor affected, so my order of checking would be;

 

1. Start engine and run, then unplug lambda connector and see if anything changes through rev range (easiest) *Remember the sensor doesn't really kick in until the engine is up to temperature (just below half on temp gauge),

2. All vacuum pipes - remove, inspect then replace taking care not to push them on too far (fiddly but not too hard),

3. Follow all wiring & check they're correctly connected including spark plug leads and temperature sensor (again fiddly but not too bad)

4. Exhaust manifold - if it's leaking exhaust then it's probably not got a good enough seal for inlet chambers, so replace (you probably already know how fiddly this is!). Are you sure all bolts on the back are correctly tightened? Like The Matt says, if the exhaust is blowing, it needs fixing, period.

5. You won't like this, but how long were you running on a broken manifold? Check compression on all cylinders. These symptoms could be a broken valve.

Most of us automatically blame the ECU on the later cars, but all of the old faults are just as likely to occur.

 

Don't give up hope yet!

 

MA

[mrducati]

If it was just the lambda sensor the car would still run but incorrectly fuelled.
Sounds like something more troublesome I'm afraid.
The MEMS ECU is tough but spiking it with a welding current isn't good (especially via the lambda as it expecting an input).
Check and repair the obvious issue with the exhaust first and see where you are.

Thank you for your advice! I didn't really think over the fact that the lambda sonde is directly connected to the ECU.

 

I'd check all the vacuum pipework & also see what happens with Lambda sensor completely disconnected (do this whilst running to see if there's a difference connected / disconnected).

 

I think you may have got away with not frying the ECU as it works. It's unlikely that you would have caused it to slightly malfunction, more likely to not function at all if damaged.

 

If you think the gasket might be damaged, the inlet could be leaking air, so making the mix weaker.

 

Exhaust shouldn't affect it that much unless a pipe is blocked or air flow around sensor affected, so my order of checking would be;

 

1. Start engine and run, then unplug lambda connector and see if anything changes through rev range (easiest) *Remember the sensor doesn't really kick in until the engine is up to temperature (just below half on temp gauge),

2. All vacuum pipes - remove, inspect then replace taking care not to push them on too far (fiddly but not too hard),

3. Follow all wiring & check they're correctly connected including spark plug leads and temperature sensor (again fiddly but not too bad)

4. Exhaust manifold - if it's leaking exhaust then it's probably not got a good enough seal for inlet chambers, so replace (you probably already know how fiddly this is!). Are you sure all bolts on the back are correctly tightened? Like The Matt says, if the exhaust is blowing, it needs fixing, period.

5. You won't like this, but how long were you running on a broken manifold? Check compression on all cylinders. These symptoms could be a broken valve.

Most of us automatically blame the ECU on the later cars, but all of the old faults are just as likely to occur.

 

Don't give up hope yet!

 

MA

I am very happy to read that there is hope that the ECU is working. Hope is restored, thank you! I do think you are totally right about the point of us automatically blaming the ECU. Even if it has a mystery-box on it, it is still the same basic engine.

 

If it is the lambda sensor, wouldn't it be running rough only when warm, since it is not sending anything before that? My engine is running rough constantly.

 

I am excited to try out your point of not pushing the vaccum pipes too far. It makes sense. I did push them on as far as I could thinking they would connect "properly". Obviosly a pipe does not connect properly when jammed on.

 

I have only driven with faulty exhaust manifold a few days. I must have ruined it when I disconnected the manifold to get space to weld the exhaust. I really hope it isn't a broken valve... The welding on the exhaust was just pre-cat.

 

Now I just need to find the time to look at it again.

[mrducati]

Hello again! This is not solved, but it is narrowed down. It turns out it is running on 3 sylinders. Curious enough all sparkplugs has a spark, making me think MiniAidas point number 5 is correct. It has also developed a smokinghabit at startup strenghtening my fear.

 

5. You won't like this, but how long were you running on a broken manifold? Check compression on all cylinders. These symptoms could be a broken valve.

Most of us automatically blame the ECU on the later cars, but all of the old faults are just as likely to occur.

 

Don't give up hope yet!

 

MA

I have not really had time to look at it properly, but a compression test is comming up.