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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 don't know if its an ignition issue, or a fuelling issue, so don't 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.
I'm 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, new fuel hoses, swapped in new plugs and a new air filter. Previous owner replaced the cap, rotor and coil. I don't 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 I'm getting a bit frustrated.
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Phil H
Posted a lot
Posts: 1,448
Club RR Member Number: 133
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Does the tacho dice to zero when it happens or still show the correct rpm?
I’m trying to remember about K-Jet as it’s been a long time since I dabbled with it - and then it was KE where you have ekectrickery bits. Iirc there’s only 2 electrical connections for K - the warm up reg and the fuel pump?
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Last Edit: Aug 31, 2019 5:18:37 GMT by Phil H
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Tacho seems to read correctly when it cuts, but thats not saying much for gauges from the early 80s.
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Phil H
Posted a lot
Posts: 1,448
Club RR Member Number: 133
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Reading something close means the LT side isn’t at fault. Hard fuel cut is feasible on EFi but I’m not sure you can even get it on CIS? I don’t think CIS actually cares about revs either - just airflow.
That suggests therefore it’s the HT side; didn’t certain distributors of that era have a rev limiter built into the rotor arm?
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Yeah, some of them did. This one has a normal rotor.
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Practical classic mag did a fault finder on these systems a while ago, as did classic ford, can’t remember when but back might be worth checking some back issues?
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Turns out the coil the previous owner fitted was a Bosch GT40 coil. A 12v coil, but still being run with a ballast resistor. Its also a coil known for causing issues when running with electronic ignition.
So reverting back to original Ford coil results in smoother running & idling, but more cut outs at random times. This is a quick video I made showing the issue. Make sure subtitles are on.
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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. 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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Phil H
Posted a lot
Posts: 1,448
Club RR Member Number: 133
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stealthstylz
Club Retro Rides Member
Posts: 14,812
Club RR Member Number: 174
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Have you checked for air leaks?
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Have you checked for air leaks? Ive checked all the intake piping, and vacuum hoses. I have a smoke machine on the way to see if there are any leaks around the intake.
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K jet is a simple mechanical system (they used a pre-cursor of it on ME109's !)and if the car has been standing you could have detritus or fuel lacquer causing an issue. I would pull the injectors and check the spray pattern. this may help
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Needs a bigger hammer mate.......
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Sept 1, 2019 10:31:32 GMT
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Maybe try running some Dipetane through the fuel system to clean out the metering head and injectors. Has the fuel filter been replaced?
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Sept 1, 2019 10:43:28 GMT
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Fuel filter has been replaced, and currently has injector cleaner in the tanks.
The plan now, is that I have a pressure testing kit on the way, along with new plenum gasket and injector O-rings. I'm going to smoke test the intake, and fuel pressure test for main and control pressures. After that, the plenum will come off, and injectors out for flow testing and to check the pattern.
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Sept 1, 2019 15:35:51 GMT
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Sounds like insufficient fuel flow to me.
Either the pump is defective or perhaps the inlet strainers (in tank or the one in the Bosch pump itself) may be clogged. Pump will tend to be noisy when it’s inlet is restricted.
More generally I’ve found that K-jet responds well to fuel system cleaner.
Nick
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1967 Triumph Vitesse convertible (old friend) 1996 Audi A6 2.5 TDI Avant (still durability testing) 1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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Sept 3, 2019 15:25:20 GMT
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This to me also sounds like fuel flow. When under load it could be that the inlet is creating enough flow to act on the mass-airflow paddle and therefore not delivering enough fuel from the metering device.
The main questions are has it done this a while or has something suddenly changed?
So many times i see k-jet performing badly due to incorrect setup. What i mean is, it could be an injector is not delivering and the system has been setup to compensate by adding more fuel. This would give the correct idle and such like but then would show issues elsewhere as in your case.
I would still recheck the ignition too however. Check the plug condition (this would give a good idea on running condition) and check things like vacuum advance etc. Check there are no vacuum leaks.
I can highly recommend an exhaust gas analyser to help set up k-jet too.
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Sept 3, 2019 16:49:00 GMT
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Does this run the same set up as the 2.9? years ago we had a TVR S3 with the 2.9 and that had issues similar and I seem to remember there being some sort of valve thing with a black & white circular disc that was the problem, it was a long time ago so may be talking complete rubbish!!
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squonk
Part of things
Posts: 855
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Many years ago I had a 2.8i Granada Estate. It used to accelerate like mad for a couple of seconds then virtually die. Cause was the electric fuel pump at the tank not being able to provide enough flow or pressure. Swapped it for one from a breaker and it cured the problem.
A fuel pressure check on the fuel line into the metering unit when under load should identify any similar issue.
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Last Edit: Sept 4, 2019 6:15:50 GMT by squonk
2004 Chevrolet Avalanche Z71 2005 Mercedes CLK320 Cabriolet 1996 Mercedes C180 Elegance Auto Saloon 1996 Rover 620Ti (Dead fuel pump) 1992 Toyota HiLux Surf 1987 Range Rover Vogue (Rusty) 1992 Range Rover Vogue SE (More Rusty) 2006 Chrysler Grand Voyager 2008 Corsa 1.4 Design
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Sept 4, 2019 11:19:24 GMT
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Thank for the replies guys. Have a lot to check and work with but waiting on a couple of things, like a fuel pressure test kit. The latest update on the car is in my project thread, which should also answer some of the questions here forum.retro-rides.org/thread/210533/kelvinators-tvr-tasmin
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Last Edit: Sept 4, 2019 11:19:43 GMT by Kelvinator
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jpr1977
Club Retro Rides Member
Posts: 656
Club RR Member Number: 18
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Sept 5, 2019 22:24:26 GMT
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I have a scan of the the KJET fault finding manual, but its a 16mb pdf, PM me your e-mail and i'll send you a copy along with a whole collection of docs i have accumulated through playing with old golf golfs for too many years... From what you have said though it does sound like a fault on the fuel side though, or even possibly the Overrun Shut-off Valve (Air Bypass) from the symptoms you mention. The below is from one of those aforementioned docs.. The overrun shut-off valve is an add on to get around an inherent problem with the basic system.When the throttle butterfly is suddenly closed (by you taking your foot off the accelerator when changing gear etc...) the airflow sensor plate tends to hang in the air whilst the air in the inlet system continuous to pass by to fill the depression or vacuum in the inlet trunking between the airflow meters plate and the now closed throttle butterfly. This of course holds the Fuel Metering Plunger in the raised position resulting in over fueling and possibly stalling of the engine. To get around this problem, an air bypass valve called the Overrun Shut-off Valve is fitted. This is plumbed in between the bottom side of the airflow metering plate and the trunking at the top side of the metering plate. It opens whenever the throttle is closed to allow direct access for air trapped below the airflow metering plate to get past and fill the void in the inlet trunking. This valve is a simple solenoid valve that is either open or closed with no in between settings. It is normally in the closed position sealing off the bypass but is activated open by a small switch on the throttle body that makes contact whenever the throttle is fully closed.This may seem at odds with the components name 'Overrun Shut-off Valve' but it effectively shuts off the fuel supply by causing the airflow sensor plates to drop back to its idle position.
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Last Edit: Sept 5, 2019 22:42:41 GMT by jpr1977
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