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Engine Miss at 2100 RPM


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Well, has anone seen this. My engine bucks and misses at 2000-2100 rpm, only when I push down on the accelerator, with the trans in 4th gear or OD, this would be under load. It does not do this below 2000 or at 2200 rpm or above. It only does this when I load the engine down. If I shift thru the gears, there is no problem. The MU and the injectors are rebuilt. the entire ignition system is new. I am running 105 psi at the MU. When the air fuel meter is hooked up to the exhaust, it shows the engine going lean during the misfiire. This would seem to be a problem with the MU? Anyone seen this before? This is very annoying. I mean, I don't run around in 4 th gear at 2.1 rpm, but it happens............

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Hi

I had the same problem, many years ago with my six. I tried everything, but could not find the reason. Checked the electric’s, checked out all the PI system. Changed all the usual bits, but could not cure the misfire.

I eventually took the car to Pumford’s, a local PI Guru. They had come across this problem once before, one a five. They had the car on their rolling road for a day and a half and after checking everything without success, started to systematically change everything on the PI system. When they changed the flexible hose to the metering unit, the misfire was cured. They checked the hose, but could not find any problems with it!

They changed the same flexible hose on my car and immediately, the problem was cured. Again the hose showed no signs of deterioration, or any reason why it should give this problem, but it worked. Try it and save your self a lot of time and effort

 

Mike G

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Hi

The conditions under which you are misfiring are those of the lowest manifold vacuum and greatest shuttle stroke.I'd be looking at the control unit if the problem was bad enough to justify it.Check and make sure all the components that move the shuttle are in good condition and free.I've read the shuttle stroke under lowest vacuum depression is 60 thou.Note if the problem was ignition I suspect you would go rich not lean during the misfire.

I hope someone thinks of something easier to check and hopefully fix the problem.

 

Regards,

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Hi

The conditions under which you are misfiring are those of the lowest manifold vacuum and greatest shuttle stroke.I'd be looking at the control unit if the problem was bad enough to justify it.Check and make sure all the components that move the shuttle are in good condition and free.I've read the shuttle stroke under lowest vacuum depression is 60 thou.Note if the problem was ignition I suspect you would go rich not lean during the misfire.

I hope someone thinks of something easier to check and hopefully fix the problem.

 

Regards,

I think you are right. I would have already pulled the MU if it was not such a pain. I would also suspect the rich condition if it was ignition, ie, raw fuel in the exhaust. Also, both of my hoses at the MU are new, of the highest quality. It is very annoying riding in the country, I had hoped it would go away. I can recheck the advance, however, it is new also, and was working perfectly. I appreciate these comments very much.
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If you want to check the fuel supply curve of the control/metering unit Egil Kvaleberg has a simple (relatively speaking) method in the Triumph section of his home page.But I believe that in doing this you are going were bold men fear to tread.

 

Regards

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Hi

Sounds very much like a problem i had last year .I tried all the usual easy things first,plugs ,points,rotor,dizzy,etc,etc.My car was very uncomfortable to drive at 30mph in 4th ,eventualy i plucked up the courage to have a look at the butterflies and although the gaps seemed ok when measured with a feeler guage when i used a ciggarette paper es suggested by others one was slightly bigger than the rest,i didnt think such a small adjustment would make such a difference but was amazed by the result its now a pleasure to drive and keeps plod happy.

John

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  • 1 month later...
Hi

I had the same problem, many years ago with my six. I tried everything, but could not find the reason. Checked the electric’s, checked out all the PI system. Changed all the usual bits, but could not cure the misfire.

I eventually took the car to Pumford’s, a local PI Guru. They had come across this problem once before, one a five. They had the car on their rolling road for a day and a half and after checking everything without success, started to systematically change everything on the PI system. When they changed the flexible hose to the metering unit, the misfire was cured. They checked the hose, but could not find any problems with it!

They changed the same flexible hose on my car and immediately, the problem was cured. Again the hose showed no signs of deterioration, or any reason why it should give this problem, but it worked. Try it and save your self a lot of time and effort

 

Mike G

This is very interesting. When I connect a 4 ft hose with gauge to my "gauge port" in the supply fuel line, the problem disappears. When I remove the hose and gauge, the problem comes back, this is immediate. I now have a braided hose in the supply line at the metering unit, I may switch to a rubber type. I believe the "pulses" from the fuel pump, in this case a Bosch, are causing the problem. When I hook the hose and gauge up, and drive the car, the pulses are being dampened by the 4 ft hose, or gauge. Your old hose may have been hard, and the new one more flexible, thus, they absorbed the pulses, and the problem was eliminated.

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If you want to check the fuel supply curve of the control/metering unit Egil Kvaleberg has a simple (relatively speaking) method in the Triumph section of his home page.But I believe that in doing this you are going were bold men fear to tread.

 

Regards

 

Hi Mike,

 

That sounds interesting...do you have a link to his home page at all?

 

Cheers

 

Tony

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