Www.VORD.net I've never been this baffled by an engine problem before. The engine started off with some occasional missing, then progressed to the point where it wouldn't start at all. I've written about the troubleshooting and included relevant specs on this page. The problem turned out to be a number of things, but mostly plug fouling caused by a weak spark. Changing the Mallory distributor for a standard electrical SD1 part has transformed the car, although I couldn't see any problems with the Mallory - just the spark was too weak. The problem was a complete pain to diagnose - this page covers the first week, but I've since spent another week on the damned thing. Getting rid of the Mallory has cured all of the other running issues I had initially put down to mixture.
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The Engine The engine is second hand. It came out of a Dakar Range Rover special after the owner decided that only a turbo charged 5.7 Chevy engine would do.
The Rover V8 is in quite a nice spec - it's a 3.9 built by RPI. It has a 270 Piper cam and runs a Mallory distributor and Edelbrock Weber 500 4 port carburetor. I've put a new set of 4.2 heads on, and made some custom exhaust headers. The engine worked really well.
The car was completed in November so I've only really driven on damp roads. It's a bit of a handful on throttle. Day 1 - The Symptoms I test drove the car on a 12 mile trip to work. It was pretty good, although the engine would occasionally miss, and became increasingly tricky to drive at low rpm. I examined the car and found the distributor vacuum advance has failed.
The plugs seemed a little lean, but I thought I'd leave that one for further evaluation later on. Having fitted the new vacuum advance the car ran really well from cold.
I took it out for test drive, and after 2 miles it started missing again. The missing got progressively worse, and the engine was definitely a few cylinders short by the time I got back to the workshop.
Had to be a weak spark - the spark kept missing while I was checking the timing. Tried a different coil and coil electrical supply. Fitted a pair of new points. I had a look around.
I found a vacuum blanking plug on one of the spare vac supplies on the carb had perished. Fitted a new one. Checked the plugs - black and sooty. Day 2 - The Breakdown Took the car for another test drive.
After 3 miles I went around a corner in 4th gear instead of second. The engine bogged down and showed no signs of recovery. I dove into a convenient lay by just as the engine conked out. It had previously worked well from cold so I let the car cool down. I checked the obvious things while I was waiting.
After an hour or so I tried again. No luck - she wouldn't start. Looked around again. Didn't start again. I walked home. Had a cup of coffee at home, then loaded my very reliable and actually working Renault with spare parts, and drove back to the MG. I tried a different coil, different leads, checked for fuel in the float chamber (present).
Tried a different supply for the coil. Battery went flat. This would be much easier in my workshop.
Drove home and called the recovery (included in the insurance). They insist on sending some bloke along to try and fix the car (what do they think I'd been doing for the last few hours - it just can't be fixed). The bloke was to turn up at some unspecified time within the next hour or so. Have another coffee, and drove back and sat in the car listening to Radio 4. It was the afternoon play - rather good. The recovery bloke turned up. He was actually pretty switched on, although he did connect up a second battery and attempt to burn out my starter motor.
The end result was 'it's got fuel, it's got spark - what else does it want?' He called the tow truck. Day 3 - Investigation Back in the workshop. Plugs are really black. It's running rich! Hey, maybe it's like when you forget to put the choke in - car runs until it gets warm then starts bogging down.
Keep on going and the plugs will get so covered in carbon that a spark just won't be possible. Cleaned the plugs up - hey it started. Then ran increasingly badly and stopped. Must be way too much fuel in there if can only run for a few seconds before fouling the plugs. Notice some overflow from the float chambers - the floats weren't correctly set so adjusted those. Mtu Engine 2018 Manual. Tried starting it off the fuel in the float chambers.
Measure the fuel pump pressure using an old tyre gauge. The manual says it should be 5psi at isle, but the tyre pressure gauge is probably not all that accurate at that sort of pressure. Maybe the spark is being easily overcome - and the misfiring is the cause of the soot - after all if it only fires every other time then there could be too much petrol left over. Try another coil, and dismantle and re-set up the distributor. Day 4 - Robert turns up to help Not such a nightmare this time as Robert has come along to help.
Actually he came along to help me fit insulation to the garage roof and some extra lighting, but I'm now fixated with this V8. It's so handy to have 2 people. We decide it's a weak spark. It's got to be the coil. Try yet another - no luck. Find another distributor cap and rotor arm.
Try that - nothing. We attach a strobe light (one of those ones that fits around the spark plug lead and works by induction). It doesn't strobe. The spark isn't sparking.
We take the spark plug out. It sparks and the strobe works. Robert talks a lot about dielectric strength and suggests the plug has more difficulty in sparking when it is at high pressure and covered in petrol. Maybe there is some breakdown in the ignition system that doesn't break down when it's easy to spark but does when it's difficult to spark. We attach the strobe to the HT lead from the coil to the distributor. Yamaha F150txr Service Manual. Looks like it's sparking 7 times out of 8. OK so there's a lead down somewhere but it should start on 7.