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The only place for a coil spring is up Zebedee's arse.
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Joined: Nov 16 2016
Posts: 914

I've seen a shortened P38 (shortened to make even better at off-roading, I forget the name of the mod 'Hog' or something... I'm sure someone will know) with extremely poor running to the point it wouldn't start on petrol even with a brand new engine because of a fuelling issue. Part of the mods on this particular example was fitting of a smaller petrol tank in the (very much shortened) luggage area. The fuel pump on this petrol tank had been sealed with some sort of silicone, it seemed this silicone had made it's way through the fuel system messing up injectors and the fuel pressure regulator. It was trailered to me, I was tasked with converting it to LPG by the owner but simultaneously tasked by the engine builder (who I know) at proving the engine he built was a good one just that the problem was with the petrol system... There was a dispute between the owner and engine builder because the owner reckoned the builder had made a dud engine, they agreed to let me find the real situation. I fitted the LPG system (mixer type) and the engine fired straight up and ran great on LPG, much to the engine builder's relief! The customer then had the option of starting and running on LPG only or fixing the petrol system, he went with running on LPG only. I could have fixed the petrol system but would probably have involved swapping out most of the bits (pump, pressure regulator and injectors) and flushing all the lines.

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Joined: Dec 30 2015
Posts: 1656

Bobcat. A mate of mine has a D90 body on a shortened RR classic chassis. Fun thing 😀

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Joined: Nov 16 2016
Posts: 914

Morat wrote:

Bobcat. A mate of mine has a D90 body on a shortened RR classic chassis. Fun thing 😀

Bobcat that's it :-)

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Joined: Apr 23 2019
Posts: 275

Well, I got the filter off, finally. Pulled every trick in the book... and didn't burn anyone/ anything. In the end I put an induction coil over the fuel union (with an extinguisher close to hand) and heated it until the canister was hot to touch (I bottled it, the induction heater will make it red hot in seconds) - nada.... Dremelled out one side of the nut on the filter housing - nada... induction heated the nut again, and slowly, reluctantly the union then came undone. I chopped open the filter and it was predictably crispy and black. So hopefully this will help the fuel pressure. Also, having replaced the rad the cooling system is running 5+ degrees cooler. That means the rail takes less heat once the engine has turned off - at 60 degrees+ on the fuel rail it will fail a restart. After 15 mins of standing the fuel rail temp was approaching 60 degrees, but now the heating up process should take longer, or maybe not even get there, as the block cools down.
I'll keep my eye on it. I also have a reflective fibre-glass wrap to add to the fuel rail if necessary.

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Joined: Dec 30 2015
Posts: 3848

Good work and a filter change can't do any harm. I'm still not convinced that heat soak is the cause of your problems. There's plenty of people who live and visit places that are far hotter than here. If that was the problem and it was a design fault, I'd have expected to have had the same problem whenever I stopped to fill up with LPG with an ambient temperature over 40 degrees.

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Joined: Apr 23 2019
Posts: 275

Sure, it cd very well be something like fuel pressure that causes it, but whatever it is, be it that, or injectors etc it only happens at 60+. Running fuel temp is normally 30-40 degrees, mainly driven by temp of fuel in the tank, heated a bit when it arrives in the engine bay, and cooled by ram air. The heating of the fuel rail after shut down is driven primarily by radiation from the engine, rather than ambient temp. My engine was running over 100 before I reworked the cooling system, yours was probably a good 5-10 degrees cooler with the super duper Direnza rad. Anyhow it's definitely a thing, I have sat and watched the fuel temp rise on nanocom to 60+ degrees, 15 mins after shut-down and it will not restart. If I restart in the 50s ie less than 15 mins, or waiting longer for the fuel rail to cool off then there's no re-start issue.

V possibly I have no issue any longer, fingers crossed

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Joined: Dec 30 2015
Posts: 3848

Can of freezer spray to chill it before trying to restart, that'd be a new one. I once had a Triumph Spitfire with twin Stromberg carbs so no accelerator pump. If I looked out the window and saw frost on the ground, I'd boil a kettle before going out to go to work. If I didn't pour hot water over the inlet manifold there was no way it was going to start.....

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Joined: Apr 23 2019
Posts: 275

Sorry, i know this has run on a long time.... Fuel pressures: now that the filter's sorted I did another test: 26 psi at idle ( not fully warmed up though), 32 if I pull the vacuum line, and 48 if I block the return ( perhaps I did a better job than last time). So that says to me that the fuel pump is OK (phew). Is that normal for the FPR too?
I suppose I can run the same test on my 4.0 if no-one else has their data to hand. I think I'll go clean the injectors next

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Joined: Aug 07 2019
Posts: 41

no not quite there yet , those pressures are at idle, the correct pressures are 36psi at idle 38psi at run give or take 2psi only , now factor in fuel use and that pressure will drop, the pump has to supply at least 2L of fuel at the correct pressure to supply the motor under full load
PS quick test stand where you can hear the pump and have some one clamp of the fuel line slowly , this will make the pump squeal under the load or it will race as the pump cavitates ,fuel pumps are positive displacement so dont close it off any longer than a couple of seconds, if you can close of the line and the pump continues to run, its stuffed. IMHO