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TVR Tasmin, Fuel Injection Fun

Well yeah, Bosch K-Jetronic…. I now understand why it’s so widely hated.

This will be a rather large post, as this covers about 6 weeks of work.

The TVR has been out of commission for a while now, since the running issue was getting worse to the point it wasn’t able to make it down the road anymore.

The last update regarding the engine saw me remove the plenum and injectors to test them. This lead to the discovery that the flow was there, but the pattern was rubbish, so new injectors were sourced.

New Bosch injectors for the cologne are big money, and I’m trying to sort this issue for minimal cost (within reason). There is a lot of discussion online about using Mercedes injectors in various KJet powered cars (mainly VW), and it all seems good, and the injectors are much cheaper. I found one single blog post on a foreign website, that once translated confirmed that the Merc injectors do indeed work on the Cologne V6. Good enough for me.

The injectors in question are Bosch part number 0437502047, and I also got new seals, Febi 034133557E. I sourced both from FCP Euro.

The Bosch boxes made me laugh. MECHANIC ONLY!

You can see the obvious difference here. The new injectors are shorter, both in the overall length, but also in the hex part at the top.

I can now confirm that these do indeed fit, and if you check the link to the other blog above, you can see that the injector does stick out into the intake tract less, but won’t be an issue (and some say is better for intake flow).

You can see the shorter hex here

These are the plastic retainers. These sit on top of the O-ring, and appear to be what actually holds the injector into the manifold, by the metal retainer pushing down on the plastic retainer, which pressed down on the O-ring. The tapered face visible in the first photo is what sits against the O-ring.

Due to the replacement injectors having a shorter hex, you cannot fit the retainer and O-ring, and then still have space to tighten the injector pipe. I found it easiest to slip the plastic retainer, O-ring and metal retainer on, leave them at the bottom of the injector, and then fit and tighten the pipe on the car. Once tight, then you slip the retainer and O-ring up into place.

So that finally solves the mystery of the injector seal. It’s a normal KJet O-ring, with a plastic retainer on it.

With the new injectors sorted, they all got refitted into the manifold and secured with the metal retainer and screw.

Next was to remove and clean the fuel distributor. This is the big weird thing on top of the air box, which feeds all the injectors. This has a plunger inside it, which the sensor plate presses up on as it opens. This plunger is known to get sticky when cars are left sitting. Mine was slow to return, and wasn’t moving as free as it should.

Carefully crack off all of the banjo fittings, including the feed and return on the side, and then remove the banjo bolts. Take care to collect all the copper washers, as there will be two on each banjo fitting. With the fuel lines disconnected this gives access to the three flat head screws that secure the unit to the air filter housing. Remove these screws. Now the distributor can be CAREFULLY removed. Make sure to slip a hand under it and stop the plunger from dropping right out. If it falls out and gets damaged, the whole distributor is a write-off!

You can see the plunger in the center of the unit.

With the unit on the bench you can turn it over and let the plunger slip out. If it doesn’t freely drop out, it may need some compressed air in the top fuel fitting to push it out. Mine dropped out OK. Be VERY careful handling the plunger, and keep it very clean.

I cleaned the plunger and its cylinder in the main unit, and sprayed and soaked all fuel ports with carb and brake cleaner.

In the injector outlets there are individual filter baskets. I used a long, thin screw to gently screw into them, and then a sharp pull freed them

They all had some traces of dirt on them, but nothing major. I soaked them in brake clean overnight and then refitted them

The regulator was the last part to clean and overhaul. This resides on the side and is a 5/8″ hex. I ordered a replacement seal kit from Delorean GO as they use the same part in their Kjet setup.

The regulator kit is PN 102807A and I also got a new seal for between the fuel distributor and airbox, PN 102855

I used a small pick to remove the old seals, and replaced them with the new green ones. The old ones looked in good shape, I wonder if they had been replaced recently to try and fix the issue? Be careful handling the regulator too, just above the o-ring in the below photo are two very small shims. These set the fuel pressure, so don’t lose them! You can add or subtract shims to increase or decrease system pressure.

I also did the o-ring on the regulator piston, but no photo of that.

That’s about all I could do with the distributor without splitting it, and that is a risky job that could result in further damage or leaks.

The next part to clean out was the (incorrectly named) Warm Up Regulator. This is the main control pressure regulator (the one above only controls the system pressure), and controls how rich or lean the engine runs. It has two bolts holding it down, two fuel banjo fittings, a power connector, and a vacuum hose.

Mine was pretty grotty. A lot of parts on the engine have been badly painted grey, which is flaking off and being ugly. I’ll deal with that another time.

I could see some dirt in the inlet mesh already, so not a good start.

There isn’t a lot to break on these, but take care taking it apart. Opening it up is easy; there are four screws on the bottom, which when removed will split the two halves.

There are a few things of interest inside the top half

  • Orange Arrow – Adjustment pin for COLD pressure
  • Green Arrow – Heater element
  • Blue Arrow – Bimetallic Strip
  • Red Arrow – “Mexican Hat” and pin

Bascially, when the engine is cold it needs a richer mixture, like a choke on a carb. A LOWER control pressure will give this result. The springs in the bottom half press on the mexican hat, which pushes on the pin, which then places pressure on the diaphragm via a little cup. This force is countered by the bimetallic strip, which pushes down on the mexican hat when cold, reducing the internal restriction. Of course you couldn’t run that rich all the time, so to lean it out when warm, the WUR is warmed by both engine ambient heat, and by a 12v heating element. This heat causes the bimetallic strip to slowly bow upwards, which releases pressure against the mexican hat, allowing it to rise up and towards the diaphragm, creating an internal restriction, raising the control pressure, and leaning the mixture. The cold pressure is set by adjusting how much the bimetallic strip pushes down on the mexican hat when cold. This is done by moving the adjustment pin up and down…. with a hammer and punch.

Anyway, to continue disassembly you need to remove the clip that retains the heater connector. A large screwdriver to lever it out does the trick

And then remove the 10mm nut from the bimetallic strip and remove it. Take note of the washer placement

This is the fuel unit containing the cup and diaphragm. I have removed two of the screws already. The cup is in the middle, filled with grease (to lubricate and retain the pin)

CAREFULLY remove the disk and diaphragm. Don’t damage the diaphragm as its hard to get a replacement (although there are some rebuild kits on eBay now which may work).

Removing these gives you access to the o-ring and fuel ports. One of them has a very fine five-layer mesh filter in it. Internet wisdom says to clean it, but not to remove it as it can cause issues with pressures if you do (reduces restriction). I hosed it from inside out with brake clean, and got a whole heap of what I can only describe as a fine sand from it. There was heaps.

After much testing, I eventually went back and actually threw the disassembled top half into my ultrasonic cleaner, which seemed to clean the filter out well. I tested it by shining a light through it, and there were some big differences in how much light came through. There was almost no light passing through at first, before cleaning.

Cool moody shot from that night

I refit the distributor and WUR, and refit the fuel pipes

I also plumbed in the fuel pressure testing kit, between the fuel distributor and WUR.

The system pressure was a little low, it should be over 5BAR

But the cold control pressure was crazy. It should be about 0.5BAR, not 3.6BAR!

Keep in mind this is after only cleaning, but without any adjustments. No wonder the car was leaning out hard. Remember, higher pressure is a leaner mixture.

This triggered the next couple of weeks messing with the system trying to iron out the pressures. I tried many things, including running the WUR naked, with no internals

And setting the pressure with the adjustment pin, located here

Then it all started to turn to custard, and the system pressure was low at about 4BAR, and wouldn’t come up even with additional shims in the regulator. This lead to buying a replacement fuel pump.

The old pump is pretty easy to remove. Four bolts hold the mount to the car, two hoses, and two wires need to be removed.

I clamped the feed hose as the tanks had fuel in them now and set about removing the pump

Pump on the bench

The pump has an inlet filter in it, and this is what came out of that filter. It’s not rust, which is good, but almost looks like fluff, some organic matter (bits of leaf?) and a lump of metal, which kinda looks like lead or solder. I might get a pre-pump filter.

The new pump is bigger and slightly longer, but otherwise a direct replacement. I couldn’t reuse the sleeve from the old pump, but reused the rubber insulator

The old pump was a Bosch 0580464125. A good pump, but mine wasn’t having a good time anymore. The replacement is a generic pump which met the required criteria (high flow, and up to 8BAR pressure).

The new pump sounds nicer, but the system pressure hasn’t changed much at all. I tried adding a whopping great washer as a shim on the regulator and finally got 5BAR pressure, but I’m sure that isn’t right. I have had the WUR open so many times now that I can open it in about 30 seconds for adjustment, but I’m still getting weird results.

Right now, the system pressure is around 5BAR with the extra shims. The cold control pressure should be about 0.5BAR (as that’s what I dropped it down to after resetting the pin) but either it’s very slow to rise on the gauge, or doesn’t rise at all now. Warm pressure is about 2BAR, 0.9BAR too low.

The new pump can obviously do the pressure, but its either being restricted or bled off somewhere. There are no leaks, and the fuel filter was replaced when I got the car (although I do now wonder about it after the pump packing a sad).

Anyway, I reassembled the intake today, and removed the pressure tester

And fired the car into life. It had some issues at first, but tweaking the mixture screw sorted that out and it idled OK, albeit a bit lumpy and revved on about 5 cylinders. The more I ran the car, the more it was happy to pick up all the cylinders and rev again. I set the idle by ear, and so far I have taken it for a dodgy run back and forth along my road, which it seemed OK. I haven’t been brave enough to take it further yet as I might take a support car with me just in case it dies in the middle of the road again.

I still want to know what the pressures are doing, but I suspect there is an issue with my pressure tester. Either that or I have a weird issue in my KJet system. I’m trying to source a second testing setup now to compare and see what happens. If I can set the pressures correctly, in theory I should be able to get a nice happy running car. Fingers crossed.

Oh, it wouldn’t be my car if it didn’t spill some coolant. Thankfully I believe this is just from me overfilling the radiator, as it was from the overflow.  Looks like it’ll need a flush at some point too.

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Tony B
Tony B
8 months ago

Actually you could just use the Merc one without the plastic sleeve and it would extend down as far as the original one!

Tony B
Tony B
Reply to  Kelvinator
7 months ago

What if you cant find the sleeve?
Cant find them anywhere