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CIS/KJET Cologne V6 dies under load at 4k rpm.


kws

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Hi all

Having some issues with my TVR Tasmin, running the factory 2.8l Ford Cologne engine. It uses K-jetronic MFI with an electronic distributor.

I dont know if its an ignition issue, or a fuelling issue, so dont even know where to start.

The car starts easily and settles into a reasonable idle. Its a bit high RPM, and if you lower the idle it runs lumpy. Thats not really the issue though.

The issue is that the car will fall flat on its face at about 4000rpm under load. Sometimes it will happen lower in the rev range, but almost without fail it dies at 4k. Revving when stationary, without load, it will happily spin out to 6k rpm.

Its not like a progressive misfire, its like the throttle is snapped shut, and the revs start dropping off. If you try and give it throttle during this, there is NOTHING. It does come back, and if youre still on the throttle it takes off with a surge, until it cuts out again. Sometimes just as it cuts it can pop and backfire.

Im feeling its possibly ignition related? Its almost like it hits a rev limiter, but i have checked and the rotor is a normal one, not a rev limiting one. If it were fuel, i feel like it wouldnt be a hard cut?

I have drained the tanks, fed it some fresh high octane fuel with injector cleaner in it, fitted a new fuel filter, swapped in new plugs and a new air filter. Previous owner replaced the cap, rotor and coil. I dont know how long this issue has been present, as i purchased the car not running, and its been off the road for about 3 years.

I would really appreciate any help in pointing me in the right direction, as im getting a bit frustrated.

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1 hour ago, kws said:

No vacuum or intake leaks

I'd be wary of a vacuum leak too, but one you don't see until vacuum is up to a certain range.

If it's ignition you'll be able to see the problem on a scope (even under no load) as you'll see the spark trail off at 4k RPM

Another culprit could be a cam chain tensioner... and perhaps it's even worth trying the engine under load with the gas cap off (to eliminate a fuel tank vacuum problem)

 

 

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Tank is vented to atmo normally (its not exactly cutting edge stuff this car) but will test with a cap open, and the cologne has cam gears. Ignition timing appeared to be spot on when i checked it with the light earlier.

I have a scope, but dont really know how to use it. Care to point me in the direction of how to check spark with it?

The cologne has about 2 vacuum hoses. I replaced the one to the vacuum advance, and the other one is for the brake booster.

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I didn't know they had gear cam drives. That's very cool.

A vacuum leak around the intake manifold or a faulty positive crankcase pressure valve miiight give the symptoms you're seeing, but it'd be a hard thing to test for as it sounds like the engine has to get to a certain load to replicate the fault.

I'd get it onto an oldschool diagnostic scope. I use to be able to read them but haven't touched one in decades so I won't pretend I know how now. I also know nothing about injection, but lots of others here do.

It seems something at 4k rpm is either preventing the right fuel/air charge going in, being ignited (perhaps the dizzy isn't retarding when it needs to), or hot gas getting out... so an exhaust problem isn't completely impossible, but it does seem an unlikely source of the issue as there shouldn't be any moving parts downstream of your exhaust valves.

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There aint much of an exhaust on this, so wouldnt think there is an issue there. I have been told to check the oil filler to see if there is suction, indicating a leaky intake manifold gasket or not.

The dizzy looked okay but seemed quite easy to move the mechanical advance when you twist the rotor by hand, but not sure if it should move that easily or if its normal. No obvious play in the shaft (heh).

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So the previous owner fitted a Bosch GT40 coil.... a 12v coil. When I checked the voltage across the terminals with the ignition on, i get about 7v. Guessing the ballast resistor is still fitted.

What would the negatives of running the coil at 7v? Obviously I wont continue to run it like that, but I cant seem to find anything saying that the effects of under volting a coil is.

E: so it also turns out it is widely known that you should not run a GT40 coil on an electronic ignition, as it can cause spark breakdown at higher rpm. Guess what im doing tomorrow.

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2 hours ago, kws said:

I have been told to check the oil filler to see if there is suction, indicating a leaky intake manifold gasket or not.

 

That's a new one on me (read: I can't see how you would get any idea of a leaking intake tract from the crankcase, but it could help confirm a PCV issue I guess)... but another diagnostic exercise would be a plug cut - i.e. go for a drive with a tool kit. Replicate the problem and immediately cut the ignition, put her in neutral and coast to the side of the road. Pull out all the sparkplugs and have a look at them for signs of wetness, fouling, overheating, lean running etc.

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Right, so some super dodgy testing including a timing light and reversing up my busy street, I can confirm that when the engine cuts out it still has spark. The timing light still flashes as the revs drop.

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Also tried another coil. Have just cleaned the KJET air flap disk thing, and throttle body. Neither made a difference, but the issue is getting much worse the more i run the car. I can't get to the end of the street now, and if I push on when it cuts out it pops and crackles from the exhaust. I suspect it may be lean?

Guess the next job is to remove the plenum and take the injectors out and see what their flow is like?

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Being a lazy bugger, I haven't checked your progress thread but when you pulled the pump/accumulator out, did everything go back exactly how it was to start with?   Possible you dislodged some crap and it went into the line post accumulator which could be starving supply at the metering head?

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