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PKH1956

Misfire after new metering unit installed

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Hi everyone, I'm really looking for help and inspiration to solve a fuel related misfire now that all logical fault finding paths seem to be exhausted!

 

Am running a 1975 CR which has been getting progressively richer during the past few years, so finally, after many attempts at tuning, the exhaust smell prompted me to exchange the metering unit. Then things got a little crazy!

 

I chose the correct MU for the CR engine and had to modify the fuel return as this version of the MU only has the screw fitting, but the car had been built at some time in the past with a push fitting pipe connection.

 

No big issue, and the replacement went really well, respecting the 'special' injection timing position ATDC of the CR engine. The car started easily and was soon running smoothly, at least for the first cautious test run of 30 miles. Then, a few miles into a higher speed run, a misfire developed :-(

 

After limping home and checking / replacing all the usual suspects (new plugs, leads, KMI injectors, fuel pressure at 100psi....) the problem would not go away, and by cracking the injector pipes, I eventually found very little fuel at Number 5.

 

Swapping the injectors confirmed that whatever injector was taken from a running cylinder and attached to Number 5 pipe, it would not spray in that position. The original Nr 5 injector worked well on another cylinder.

 

So suspicion fell on the none return valves in the Banjo unions, and two new Banjos were purchased (KMI) and installed. The Nr 5 pipe was also checked for blockages and this appeared okay. The misfire still persisted!

 

So phone call through the Metering Unit supply chain resulted in the MU being exchanged for a newly refurbished one, which was fitted with due care a couple of days ago. PERFECT :-) .... for a few miles, then the misfire returned :-(

 

Again, fault finding proved that whatever injector (now new ones) was fitted onto Nr 5. it would not spray! But the one taken from Nr 5 works on other cylinders! Swapping the Banjo's was also tried to see whether the problem moved to Number 2 - it stayed on Number 5!!!

 

So any gems of inspiration, or preferably someone saying they know exactly what the problem is, would be appreciated.

 

Living in hope

 

Phil

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So your saying if you pull the injector with the engine running there is NO fuel spray at all?

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That's right - even when you crack the pipe the flow of fuel is much less than cracking the pipe on another cylinder.

 

Put any injector on Nr5 and there is at best a small dribble at high speed. The same injector on another pipe demonstrates a good conical spray throughout the engine RPM range.

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Phil,

What you say excludes the injector and the M/u itself, if the unlikely circumstance of two restored units having the same fault is excluded (Pace, Sherlock Holmes!) and points to something between them.

 

The injector hose must be first suspect. Blocked? But you say not. Replace the hose?

Then, you have replaced the banjos (banjoes?), but there is a filter inside those. How complete was the replacement M/u, or the original restored one, and how much of your OE kit went back on it? Could that filter be at fault?

John

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Hi everyone, I'm really looking for help and inspiration to solve a fuel related misfire now that all logical fault finding paths seem to be exhausted!

 

Am running a 1975 CR which has been getting progressively richer during the past few years, so finally, after many attempts at tuning, the exhaust smell prompted me to exchange the metering unit. Then things got a little crazy!

 

I chose the correct MU for the CR engine and had to modify the fuel return as this version of the MU only has the screw fitting, but the car had been built at some time in the past with a push fitting pipe connection.

 

No big issue, and the replacement went really well, respecting the 'special' injection timing position ATDC of the CR engine. The car started easily and was soon running smoothly, at least for the first cautious test run of 30 miles. Then, a few miles into a higher speed run, a misfire developed :-(

 

After limping home and checking / replacing all the usual suspects (new plugs, leads, KMI injectors, fuel pressure at 100psi....) the problem would not go away, and by cracking the injector pipes, I eventually found very little fuel at Number 5.

 

Swapping the injectors confirmed that whatever injector was taken from a running cylinder and attached to Number 5 pipe, it would not spray in that position. The original Nr 5 injector worked well on another cylinder.

 

So suspicion fell on the none return valves in the Banjo unions, and two new Banjos were purchased (KMI) and installed. The Nr 5 pipe was also checked for blockages and this appeared okay. The misfire still persisted!

 

So phone call through the Metering Unit supply chain resulted in the MU being exchanged for a newly refurbished one, which was fitted with due care a couple of days ago. PERFECT :-) .... for a few miles, then the misfire returned :-(

 

Again, fault finding proved that whatever injector (now new ones) was fitted onto Nr 5. it would not spray! But the one taken from Nr 5 works on other cylinders! Swapping the Banjo's was also tried to see whether the problem moved to Number 2 - it stayed on Number 5!!!

 

So any gems of inspiration, or preferably someone saying they know exactly what the problem is, would be appreciated.

 

Living in hope

 

Phil

Hi Phil.

 

When you disconnected the fuel line/ injector for No 5 did you check that it was not being restricted by bits of rubber O ring from the original sealing banjo O ring non return valve, as this happened to me about 5 years ago. The hole in the right angle fitting or banjo are not very big? Both O rings on my car for 2 & 5 were breaking up, bits of rubber also in those injectors, some were quite large.

 

Bruce.

 

Bruce.

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Thanks John

 

I'm with you on the Sherlock Holmes deductions about the MU, and will replace the pipe as soon as I get one - even though the current one looked clean and blew through easily in both directions.

 

The banjos are both new, and have also had their positions swapped. Will examine them more for any contamination on their next outing (am getting very fast at MU removal now!).

 

The MU was a KMI service exchange unit, so came complete and was supplied with new O Rings for the banjoes.

 

Phil

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Thanks also Bruce - I did a visual and blew through the pipe both ways - will take a closer look tonight

 

When taking the original MU off, the O Rings were intact and the bolts quite tight.

 

Phil

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You have to install #2 and 5 hoses with the MU off the car, assume you did.

Trying to rotate the union while almost tight will damage the O-rings, they need to be installed with great care.

The injectors do have a fine filter in them, plastic. See if you find any debris (rubber) in those.

Good luck,

Waldi

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Hi Phil,

 

I had this problem a couple of weeks ago. I took the injector off and no fuel. I run the engine, with the fuel pipe in a glass jar, and eventually fuel started to appear I put the injector back on and it was fine. . I had to do this on 1, 5, and 6 injectors it took a while for the fuel to come through. It was a big air lock in the system.

 

I hope this helps.

 

Kind Regards,

 

Dave from sunny Spain

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The story now come to an end - hopefully!  I obtained a Nr.5 pipe (thanks to Leslie Brown, the Bavarian Triumph Emporium!) but before fitting it I pulled the injectors out do double check where the misfire was.  This time it was Nr.6 that did not spray, and replacing that injector cured the fault.  Have since covered a couple of hundred miles, including Autobahn, and things seem fine.  The car drives much more smoothly with a CR MU on a CR engine!

As the faulty injector had previously been in in Nr5, I can only imagine that some dirt was in the pipe which found its way into the injector that I then moved to 6 during the fault finding.

Thanks to everyone for their ideas and contributions, I'll be back for more inspiration when the TR confuses me again!

 

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