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Discussion Starter #1
Hi, any help would be greatly appreciated.

I have a GTV6 1983 that is missfiring under load at about 4000-5000 rpm, and lacks power. I can put my foot to the floor and it will just stay at the same speed, until it finally clears up and takes off.

I have recently replaced the combi relay, as it was turning the fuel pump on at ignition. All plugs have recently been changed. The car has sat for three years or so, but in the last 6 months has been started reguarly.

Can anyone help me out here, it's driving me crazy.

Thanks
 

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The engine needs three things to run - compression, fuel & spark. Assuming no big holes in the block and engine parts strewn about I think it is safe to assume no mechanical derangements.

How old is the coil, rotor/cap & ignition wires? That could explain a misfire but it wouldn't then suddenly 'clear up and take off'.

That leaves fuel. Gasoline does not store well. Was it treated for storage? I use Stabil for any gas that isn't going to be used/replaced for a few weeks. The fuel injectors could be partially plugged. If so, there is little you can put into the tank to really clear them out. There are places that will clean them in an ultrasonic bath and cycle solvent through them.
 

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eric's right in his comments on the fuel. I used my Biturbo as a daily driver for 14 months while restoring my GTV6. Then the Bitrouble sat fir 18 months; we all know things go longer than originally anticipated; and the gas went bad w/o Stabil. F'me! Lost 4 injectors beyond repair from an injector service center!! New ones aren't cheap and although the Marellis are identical in the standard BMW type Bosch ones their wapjob resistance is different of course.

I'd flush the complete fuel system regardless due to the long lenth of sitting. I bought an '86 GTV6 that sat for 3 years after a few miles on a full rebuilt motor that wouldn't run. Smelled the fuel tank gas and sure enuf - varnish. At least the injectors cleaned up.

Also, what is the condition of the cat. Had a similar condition on the old style ceramic POSs. I hawged out my current GTV6 original cat and thought I'd installed a sport motor! You should have seen the clogged crap that came out!!

How's the dist cap, rotor and timing?
 

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Well, the thing you can do is to gather more information so that you can narrow down the possibilities.

I like to make a decision on whether a problem is electrical or fuel and then
try to prove it by going from component to component to see if it's within
specs.

It sounds like it's running lean, and then getting enough fuel to get closer to the correct mixture.

If your foot is planted on the floor, the fuel injection is not trying to make any radical adjustments so maybe the fuel flow isn't sufficient. That's my
theory, so prove me wrong.

You can put a pressure gauge in the fuel line by disconnecting the cold start
hose and then running the line out from under the hood and trapping it in place under the windshield wiper, then go drive it and see what happens to
the pressure as you get into the problem area.

Either it's ok or it's not. If it's not, do the simplest, cheapest things first:
check the return pressure from the pressure regulator by adding a tee and then attaching the pressure gauge there. Replace the fuel filter.

You don't really have to drive your car to do any of this, you can turn on
your ignition, take off the air cleaner cover and push the air door open with
your finger to start the fuel pump.

I guess you can't rule out clogged injectors, but my experience has been that if they aren't flowing enough fuel, they don't usually suddenly start at high rpms. Carburators, sometimes, fuel injection, not so much. Of course that is just my experience.

I made a test rig when I checked my injectors out once I removed them and used a not-very-volatile solvent to keep the explosions relegated to the combustion chamber where they belong.

So maybe the fuel pressure is perfect, then have someone run the motor up to 2500 in dim light so you can look for arcing from the plug wires. What do the plugs look like? Are they black or dark gray or light gray?

Use a timing light and have someone slowly run the engine up to 5k to see what the timing is doing.

My '84 had been sitting for 5 years and what prevented it from starting
was rust/crap all settled in tightly at the banjo fitting on the bottom of the
fuel tank. Of course I started at the other end of the car so it took me
a while to find it.

Please, no offense intended, but not knowing your level of mechanical expertise, I'll add that if you have any doubts about doing this kind of stuff, then don't do it and start with some fuel injection cleaner in the gas tank.

Schaeffer
 

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One other thought. The 'L' in L-jetronic stands for the German word for air (luft). L-jet uses the air flow measurement to calculate how much fuel to inject. So, if the air flow measurements are off the computer won't send the right signals for how much fuel to inject. Check the flap in the AFM to make sure it isn't sticking. And check all the intake air & vacuum hoses for leaks, looseness, etc.
 

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Discussion Starter #6
Thankyou for the replys, it has given me more idea's.

I am fairly confident the problem is something to do with the cars ignition coil and timing.

I will go through that list and update on what the problem is.

Thanks for all your help.
 

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By the way guys, what is the best way to drain the fuel out of the tank on a 75? We have one that has been standing for over a year. I didn't find out about Stabil until it had already been sitting for several months unfortunately.
 

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Siphon. I suppose you could disconnect a fuel line, aim it into a suitable container, connect 12V to the fuel pump and pump it out, too. The GTV6 has a fitting on the bottom of the tank. But even if is not seized in place, draining fuel there can lead to an armpit full of gasoline.

umm, don't smoke...
 

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Actually, the original Owner's Manual has very good electrical diagrams for specific sections; e.g. lighting, L-Jetronic Fuel Injection, relays, fuse layout, etc.
 
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