Decat missfire
Discussion
As some of you know I'm the new proud owner of a fire breathing cerb. Well not so fire breathing as it happens!
Couple of questions, today had a chance to spend some time with the car and drove to diss and back. There is a missfire under load almost sounds like the engine is pinking as if timing not spot on. Also backfires every now and again.
The car has the cats removed, will this cause these symptoms if ecu has not been remapped?
I haven't had chance to check the obvious things like he leads etc, however will be my first thing to check.
Anyway look forward to some tinkering with some helpful advice along the way.
Couple of questions, today had a chance to spend some time with the car and drove to diss and back. There is a missfire under load almost sounds like the engine is pinking as if timing not spot on. Also backfires every now and again.
The car has the cats removed, will this cause these symptoms if ecu has not been remapped?
I haven't had chance to check the obvious things like he leads etc, however will be my first thing to check.
Anyway look forward to some tinkering with some helpful advice along the way.
The Cerbera is noisy with and without a decat as it tends to run rich at many points of the timing curve. It will often burn unspent fuel in the exhaust (the pops and bangs associated with misfiring) explosively but this is not a misfire as such.
The stuttering or loss of power is usually a different issue and can relate to a number of things, but not likely the decat.
If the electrical circuits aren't at full charge and working order, the engine can be unhappy. Battery charge, big fuse or loose connections (earth, HT leads, etc).
It could also be a sign that one of the lambda sensors is knackered and giving the ECU false readings.
Finally, a standard map on a 4.5 can often have a flat spot at around 2000 rpm.
The stuttering or loss of power is usually a different issue and can relate to a number of things, but not likely the decat.
If the electrical circuits aren't at full charge and working order, the engine can be unhappy. Battery charge, big fuse or loose connections (earth, HT leads, etc).
It could also be a sign that one of the lambda sensors is knackered and giving the ECU false readings.
Finally, a standard map on a 4.5 can often have a flat spot at around 2000 rpm.
Strange you mention lamba sensor, it appears it failed last mot due to a lamb sensor fault. Will check folder for receipts to see if replaced.
It is almost as if it's running to advanced as not a lot of va va vroom, and you can feel the missfire. I suspect a faulty connection somewhere as every now and a going for a second or two it sound as if firing on all 8.
It is almost as if it's running to advanced as not a lot of va va vroom, and you can feel the missfire. I suspect a faulty connection somewhere as every now and a going for a second or two it sound as if firing on all 8.
If the car was from a dealer I would simply return it to them and get them to report on and fix the problem. The law protects consumers from faulty goods even if second hand, and to sell a car with a misfire even if it develops just after the sale, well they are responsible for sorting it. Best of luck.
It was bought at auction on 2nd March so that's not possible.
I must add that it's not completely 'caveat emptor' at auctions. I know of a 1939 MG car returned to an auction house when it was discovered the engine block was cracked. Not disclosed at sale and sufficiently serious enough for this to be accepted.
A misfire that develops hundreds of miles later would not be one of these. The Cerbera is advanced (enough) to enable connecting to the ECU to interrogate it for faults. Without the correct leads or software this will need a visit to a specialist.
I must add that it's not completely 'caveat emptor' at auctions. I know of a 1939 MG car returned to an auction house when it was discovered the engine block was cracked. Not disclosed at sale and sufficiently serious enough for this to be accepted.
A misfire that develops hundreds of miles later would not be one of these. The Cerbera is advanced (enough) to enable connecting to the ECU to interrogate it for faults. Without the correct leads or software this will need a visit to a specialist.
Edited by ianwayne on Wednesday 20th March 08:07
That is risk buying at auction, but always aware there may be sneaky reason someone puts there treasured through auction. Classic car auctions tend different to normal car auctions, but not always! I bought it open minded that if there were any issues, it gives me a great excuse to hide away in the man cave!
Will not get chance to investigate until next week. I had a highly tuned mgb GT Sebring recreation, displayed very similar symptoms. Turned out to be head gasket, having said that there is non of the other symptoms, over heating, mayo in oil etc.
But that could explain emmision problems at mot?
As for software which is best to download, I have various leads so onecshould fit but if three pin I will make one up.
Fingers crossed it is electrical.
Will not get chance to investigate until next week. I had a highly tuned mgb GT Sebring recreation, displayed very similar symptoms. Turned out to be head gasket, having said that there is non of the other symptoms, over heating, mayo in oil etc.
But that could explain emmision problems at mot?
As for software which is best to download, I have various leads so onecshould fit but if three pin I will make one up.
Fingers crossed it is electrical.
Jhonno said:
I think EvoOli did an updated Windows version of the TVR Diagnostics..
Or RS-AJP for Android is what I use..
Just to say you can run any of the 3 platforms out there quite happilyOr RS-AJP for Android is what I use..
- EvoOli's Windows needs XP, but I just run a Virtual Machine on my laptop with the free XP image download from Microsoft and it works great (I use a Mac BTW!)
https://www.pistonheads.com/gassing/topic.asp?t=13...
- RS-AJP Ade's great Android App - now free!
https://play.google.com/store/apps/details?id=com....
- RSi-AJP iPhone Greg's version on iPhone - also awesome
http://rsiajp.com/index.php/en/
Also worth doing some old school checks like inspecting the spark plugs
Hopefully you won't find one looking like the odd one out here
I chose to ignore it, assuming it was oil contamination due to leaking piston rings
In fact it was a valve guide that had worked loose in the head, which could have resulted in valve stem failure
That would have been very bad indeed
Hopefully you won't find one looking like the odd one out here
I chose to ignore it, assuming it was oil contamination due to leaking piston rings
In fact it was a valve guide that had worked loose in the head, which could have resulted in valve stem failure
That would have been very bad indeed
All good advice.
However, my misfire that ran for ages was literally a ht lead not connected properly on a coil (#5). They all looked fine until I pressed this one harder and it moved off the coil stem! The coils are a pita to reach normally and you need to ensure all are connected properly.
EvoOllie’s diagnostic software runs on any windows program - up to Win 10 I believe and I have found this to be totally reliable and easy to use.
However, my misfire that ran for ages was literally a ht lead not connected properly on a coil (#5). They all looked fine until I pressed this one harder and it moved off the coil stem! The coils are a pita to reach normally and you need to ensure all are connected properly.
EvoOllie’s diagnostic software runs on any windows program - up to Win 10 I believe and I have found this to be totally reliable and easy to use.
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