Hi guys,

Yesterday I started having some pretty bad problems with my car. When accellerating every now and then (approx 50-60% of the time) the car is misfiring. Looking at the boost gauge, its happening when the gauge is roughly sitting on 0, and its fluctuating just below the zero mark. Funnily enough, if I give it a bit more throttle she seems to come good. This is making me think that the bypass valve may be coming into play?

The second problem is that every now and then when I'm accellerating the car will be seeing boost (partial throttle - say 5psi) it'll shoot down to ~-25 for a second and then come back to 5. Again, this is making me think bypass valve.

Unfortunatly, because the Australian cars are not OBDII complient, I cannot read any fault codes.

The specs of the car possibly relevent to this problem are:
2003 Cooper S, 17% Reduction Pulley, Headers w/ no cat, Alta intake, ported/polished head with 1mm bigger valves/shrick race cam, JCW plugs, JCW 380cc injectors. All of these mods have been running for at least 6 months with no issues whatsoever.

Things I've checked:
- plugs - full of carbon from misfiring, cleaned, look perfect
- injectors - pulled out, gave them a good looking at, no apparent problems
- plug wires - changed

Am I correct in thinking the bypass valve could be the culprit?
I'm trying to avoid a trip to the dealers, and if it is the bypass valve I'll just replace it with a Detroit Tuned one.

I seem to recall from the yo-yo thread that there is a line you can cable tie which effectively keeps the bypass valve open/disabled, economy goes to rubbish but I'm thinking of trying that to prove if its bypass valve related.

Any opinions/ideas?

Cheers

Kev

 

man check your plugs and wires and coil and connection to coil. i had a hell of a time finding this ;as my computer kept saying just #4 misfire. it turned out to be the coil pack. it was really bad at partial throttle and quick blips. it would break up so bad it would go into limp. then it would clear up . finally it stuck so i had the old coil still and finally said why not . BINGO!! all set. good luck . btw auto zone will scan for free if you don't have one. i highly recommend the one sold bye sears though. it'll do old and new, foreign and domestic. lata.

 

Hi Herb,

Like I said, checked the plugs OK, replaced the wires OK, connection to coil is OK. Don't have a spare coil to check it with. For what its worth, car has never gone into limp mode.

Also, like I said I'm in Australia, and we don't have OBDII complient cars - we can't use a scan tool to read fault codes.

 

Reading the yo-yo thread, first post:
This is pretty much what I'm seeing...

 

well that might explain the yo yo but what of the misfiring?

 

if your bypass were stuck closed(as does happen on occasion) it will give a stumble ; i had this happen . but i wasn't getting misfires. you could pull it out to see if it wore a groove or whatever and is sticking.

 

I'm thinking that they might be related... thinking the misfiring might be because its expecting air, and not getting it .

 

zip tie your bp valve shut and test drive. If the problem is gone, replace it.

 

Thats what I'm planning on doing in the morning (going to bed now) - just had to work 3pm till 3am, yay.