One for you 8inaV

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robp38

robp38

Well-Known Member
Posts
2,503
Location
north devon
richard phoned you the other week about my heap 4.6 v8 2000, you said it could be the cats have broken up and are blocking the exhaust.

thought i would test this theory ( and **** off the neighbours at the same time :D) so i dropped the exhaust off from the manifolds and started the car hehehehehe! what a noise... but she still wont run.. revs wont settle and pumping the pedal makes little difference... my thought is if i try to run the car with the zorst off then the lambda sensors are not reading anything so it wont run to well,, am i right in thinking this... really need to get this car running now... have had to resort to driving a 96 mondeo:mad:

any suggestions are welcome ( allready got the petrol n matches waiting)
 
As I understand it the lambdas are not used when you first start up ( open loop ) these don't kick in until they have warmed up and the fuelling is adjusted relative to the feedback they are giving ( closed loop ). During the open loop phase the ecu uses the long term trim values to approximate the fuelling so I would expect that unless you had the adaptions reset before your experiment, she would still run rough.
 
confused now...

she runs badly with or without the pipes attached.. according to testbook all fuel trims air etc are within tollerance and shows no faults.... HELP!!!!!!!!!!!!
 
rewmer said:
As I understand it the lambdas are not used when you first start up ( open loop ) these don't kick in until they have warmed up and the fuelling is adjusted relative to the feedback they are giving ( closed loop ). During the open loop phase the ecu uses the long term trim values to approximate the fuelling so I would expect that unless you had the adaptions reset before your experiment, she would still run rough.
Click to expand...

robp38 said:
confused now...
Click to expand...


If you put it on testbook again, you'll find an option to reset the ECU. It will go to factory defaults and then start the process of gradually learning again.
 
rasheed said:
If you put it on testbook again, you'll find an option to reset the ECU. It will go to factory defaults and then start the process of gradually learning again.
Click to expand...

richard done a rest on it.. so i just gotta keep it runnoing a while whilst it relearns things ???
 
robp38 said:
richard done a rest on it.. so i just gotta keep it runnoing a while whilst it relearns things ???
Click to expand...

robp38 said:
i dropped the exhaust off from the manifolds
Click to expand...

rewmer said:
As I understand it the lambdas are not used when you first start up ( open loop ) these don't kick in until they have warmed up and the fuelling is adjusted relative to the feedback they are giving ( closed loop ).
Click to expand...

No I don't think you should have to wait for the ECU to relearn as it only does that gradually over time. She should actually run pretty smooth after a reset. My theory is 4 things go into smooth ignitions, fuel, air, spark and timing. All the ECU does is keep adjusting those to suit conditions. If the ECU is unable, then there's probably a physical problem, like poor spark or worn injectors, failed MAF or air temp sensors, low fuel pressure etc. But based on what Rewmers saying, maybe you should first try dropping the exhaust after the lambdas instead of taking it off at the manifold and taking the lambdas out of play completely. Maybe the ECU is waiting for some kind of signal from them.

Just things I would try mate. Hope something works out for you.
 
rasheed said:
No I don't think you should have to wait for the ECU to relearn as it only does that gradually over time. She should actually run pretty smooth after a reset. My theory is 4 things go into smooth ignitions, fuel, air, spark and timing. All the ECU does is keep adjusting those to suit conditions. If the ECU is unable, then there's probably a physical problem, like poor spark or worn injectors, failed MAF or air temp sensors, low fuel pressure etc. But based on what Rewmers saying, maybe you should first try dropping the exhaust after the lambdas instead of taking it off at the manifold and taking the lambdas out of play completely. Maybe the ECU is waiting for some kind of signal from them.

Just things I would try mate. Hope something works out for you.
Click to expand...

tried that first..tried clearing out exhaust with a coathanger,, got a few bits of crap out but made no difference to the running... would a knackered maf always show on test book ?

sorry just getting desperate to get it running before the misses
finds the matches!!!!!!!!!!!!
 
Hi Rob - No luck yet?

The theory was that the 2 cats had broken up and had possibly clogged/blocked the pipe at the 'Y' section, where the 2 downpipes meet up. I can see the logic in this.

After a reset, the engine ECU starts from default settings, so as mentioned, the car should run reasonably well. However, in your case it actually ran worse. I'm not sure why this could be except if something mechanical wasn't right.

The MAF is working OK. T4 won't always get a stored fault code from a non-working sensor. You need to look on live data to check the readings, and we did that. Sometimes it throws a code blaming something else (such as an oxygen sensor when it is MAF or manifold air leak), but you need to be aware of this.

Your fuelling was perhaps a clue in putting the blocked exhaust theory on the table. The trims for both banks were showing 1.4:1 ratio. In other words (IIRC) the engine was trying to fuel. 1:1 is what I understand to be about right, but I may be wrong.
 
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