misfire sounds like running on 3 cylinders

[joedeltahf]

any ideas welcome

As above - does it hot and cold

when it first started two nights ago i only noticed as it stalled at a junction and idled very badly if atall but seemed to be driving ok.

it was cold today but just revving on the drive sounded rough through the lower part of the range

I pulled off each ht lead in turn and was equally worse

seems to be an unburnt fuel smell at the exhaust

have changed
MAF
Coil pack and HT leads

but both to no avail.

could it be exhaust /cat related as I had hit some big puddles at speed the night it started.

thanks

 

[oilburner]

You've ruled out pretty much everything else so you need to get the compression tested on the cylinders, sounds like it's sucked up some water and hydro locked the engine though

 

[tuonokid]

Hi Guys
I think the hydro locked up situation is a little severe as it would affect all the cylinders and on a STD Puma the air intake is at the bottom of the A post. There's nowt wrong with a compression test but I would look for drying out all the cars electrics (plugs) before I went further.
Barry

 

[Wild E. Coyote]

If you can smell the unburnt fuel, I'd have a look at lambda…?

 

[AndyPuma]

Have you seen the answer to the other issue I raised yesterday?
http://www.projectpuma.com/viewtopic.php?f=25&t=26627
It could be an unmonitored air leak running weak / lumpy on no specific cylinder.
Check out post MAF intake manifold & crankcase pipe work for air leaks (crankcase breather, purge line, fuel pressure regulator, servo etc. Also joints, throttle body to manifold, manifold to head etc. I found my leak by hearing a hissing and my dad sprayed fuel around the intake (he's a danger man). The vapour is pulled in to the manifold where it leaked and temporarily stopped it running weak and the misfire cleared for a short time. You can use WD40 too with a straw if you don't like the idea of fuel! Don't spray around the air intake itself because that's an intentional leak!
My dad (ex petrol engine calibration engineer) says that smelling unburned fuel at the exhaust is very misleading with most people saying its rich or misfiring but it's impossible to say what cylinder is missing or that it's rich, as unburned cylinders due to weak misfire push out lots of HC's also!

 

[joedeltahf]

thanks people

the air filter didnt seem wet so dont think ive sucked up a load of water biut good point, I shall be moving the inlet for future

was thinking air leak but coundlt find any, will have another look this weekend, got a spares car so can try swapping lamda, tps etc

 

[joedeltahf]

oh so have now changed in total

maf
coil pack
ht leads
plugs
tps
idle control valve
cam sensor (left side on rocker)
gasket sealed inlet manifold 1st stage (not at cylinder head)
checked t piece crankcase breather tubes
checked compression and all are equal



and.................

still have the misfire - light throttle and idle !!!

only thing i havent tried is the lambda sensors - I have pre and post cat

I unpluged the pre but didnt make any difference though the engine had not properly warmed up

have a 421 system with one lambda to fit and tape ecu so have started on this

I am still thinking its an inlet air leak though - has anyone found any of these before? or is it more likley its the lambda?

Also if i swap the ecu do i need to change keys/ chips etc ? or is the imobiliser alarm not part of the ecu?

 

[jimfrp88]

Have you plugged it in to a code reader?

When was the fuel filter last replaced?

 

[joedeltahf]

ive run the check on the dash but no fault codes so i assume a code reader will be the same

will try a fuel filter for the cost its worth a try but it seems to be over fueling rather than under fueling

 

[oilburner]

The dash trick won't do you any good, it only shows DTCs relating to the clocks

 

[r53bertyboo]

Have you done a compression test? Worth checking here too

 

[Ian G]

First things first, stop throwing money at something which you haven't diagnosed at all.

Your assumption that a proper code reader won't be any use is incorrect, it'll be a lot cheaper and easier than your current approach.

 

[joedeltahf]

compression checks out ok

i have a spares car so have just swapped parts so cost is £0.00 and yes that one did and still does run fine.

 

[DOH]

What readings were you getting on the compression test across all 4 cylinders?

 

[joedeltahf]

120 on each

fault code reader has arrived so will have ago with it on sat

 

[DOH]

the fact that they are all the same is good, however 120 psi, something is wrong with the compression tester or the way you have performed the test.

Did you get the engine to normal operating temperature remove all plugs, disconnect coil pack connector, remove fuel pump fuse and crank over with your accelerator to the floor? If you did and only got 120psi ,then you have problems with piston rings sticking.

You should be getting 180 psi -200 psi per cylinder. even an aircooled beetle with low compression engine has 150 psi compressions.

 

[DOH]

The fact that they are all the same is good, however 120 psi? Something is wrong with the compression tester or the way you have performed the test.

Did you get the engine to normal operating temperature remove all plugs, disconnect coil pack connector, remove fuel pump fuse and crank over with your accelerator to the floor? If you did and only got 120psi ,then you have problems with piston rings sticking.

You should be getting 180 psi -200 psi per cylinder. even a VW aircooled Beetle with low compression engine has a compression of 150 psi .

 

[Ian G]

fault code reader has arrived so will have ago with it on sat

That's better news, will wait to see the results of that.

 

[joedeltahf]

the compression tester threads are not long enough to screw in and the engine was cold, used the push on adaptor so prob why readings are low, did 2 checks and all seem to be equal compression, engines seems fine on full throttle so dont think there is an internal fault just wanted to make sure they were equal with the compression test.

 

[DOH]

In other words, your readings are totally meaningless as that is not the correct way to do a compression test! If the engine in the other car runs ok,would it be quicker to remove and fit that? Rather than not being able to diagnose what the problem actually is and substituting parts from a donor car . It would also be beneficial for you to contact a recommended mechanic, who is good at diagnosing problems (not all are). This will save you an awful lot of time. That would cost approx 1hrs labour. You could then carry out the fix based on the mechanics findings to keep costs down. Purchasing a fault code reader is a good move, however, be aware that very often fault codes throw up on the ecu, because of an associated problem. Therefore they aren't always definitive. Having a good understanding of symptoms,taking accurate readings and having expertise to interpret them,will be beneficial to you. I would also recommend that you repeat the compression test with the help of an assistant and use either a tester with a rubber cone bung or purchase a long reach 14mm adapter, Gunsons make one,to screw onto your tester, such as:
http://www.ebay.co.uk/itm/GUNSON-G4...036?pt=LH_DefaultDomain_3&hash=item2c68763fac