Maybe needs to go to the electrical forum, but it's a definite HELP ME!!

Some info! 75 280Z running an L28ET on Megasquirt II with an EDIS system. Problem SHOULD NOT rest with these components. Should be a general car problem.

Alternator converted to internally regulated via thread mentioned here:

http://www.atlanticz.ca/zclub/techtips/alternatorswap/index.html

Bought the car needing a fuel pump. Replaced the fuel pump. Found out the car doesn't recharge the battery.

-Battery's GOOD.

-Alternator's GOOD. ( on my 3rd alt now! First one tested good, then bad. 2nd was from a parts car, good then bad. 3rd is definitely GOOD )

-Wiring going to L and S connections ( exciter and sense ) for the alt input is GOOD ( checked this myself and had this checked by an alternator shop...which told me the alt I had in the car was bad and that my wiring was GOOD ).

So by the guy's recommendation, In had the alt swapped for a known GOOD unit. Throw the thing in the car, and what do you know, no dice.

Runs around 12.1V across the battery. Car doesn't charge sitting at idle. Will charge around 13.0V around 3000RPM, far lower than the 14.45V that the sense connection aims for out of the alternator.

Fuel pressure should be 40psi at idle. I get 36psi. Upon increasing RPM, the fuel pressure increases to about 40psi ( it should increase ), and then drops down to about 33psi. I'm thinking low voltage across the pump is causing it to lose fuel pressure.

I'm going to tear my hair out trying to figure out what's wrong! :stupid:

Any ideas??? I've been at this for a MONTH.

OH YEAH. Doesn't like to start. At all. Will start and die. Takes about 5 start and dies before it will start and run, and will run very low at 500RPM.

Ok, it is obviously not the Alternator.

I strongly suggest that you go back over your conversion wiring again. It sounds like you are not getting any excitation voltage to the internal regulator. (or it is wired to the wrong pin.)

As far as the fuel pressure goes, electrical wouldn't effect it. Unregulated, that pump would put out somewnere in the vicinity of 100 psi. Manifold vacuum actually controls the fuel pressure through the fuel pressuse regulator so even if the voltage was slightly down it wouldn't make enough difference to matter.

EDIT: I have no clue about Megasquirt. What I said assumes a stock fuel pressure regulator.

Edited May 21, 200915 yr by sblake01

Ok, it is obviously not the Alternator.

I strongly suggest that you go back over your conversion wiring again. It sounds like you are not getting any excitation voltage to the internal regulator. (or it is wired to the wrong pin.)

See that's the funny thing. I checked and took her to an alternator shop to check over the wiring.

I get a full 12V at both the L and S connections ( the L is the excitation wire ), when ON ( The L should be 0V when not ON, which it is ).

The crossovers connections as mentioned in the conversion thread were rewired a few days ago and they are good.

The car has been running on an internally regulated alternator for well over a year, so the wiring had BETTER BE good ha.

As far as the fuel pressure goes, electrical wouldn't effect it. Unregulated, that pump would put out somewnere in the vicinity of 100 psi. Manifold vacuum actually controls the fuel pressure through the fuel pressuse regulator so even if the voltage was slightly down it wouldn't make enough difference to matter.

EDIT: I have no clue about Megasquirt. What I said assumes a stock fuel pressure regulator.

You might be on to something, but I'm not sure.

The Aeromotive FPR that's on the car is supposed to increase the pressure at a 1:1 psi ratio fuel pressure: manifold pressure.

Regardless, I do have a charging problem. If it takes care of my fuel pressure problem in the process, then great.

You may have a floating ground. Can't hurt to try. I'd remove and clean the battery to body ground, making sure you have a bare metal contact between the two. - - and I'd add a good ground between the body and engine.

good luck,

Carl B.

I agree with Carl also check the ground to the body from the alternator. I do not remember how the 280 is wired but, this is a classic problem with the earlier cars.

I had the samre problem with mine Alt conversion.

I cleaned all conections and made sure there was a solid ground and all was fixed.

I had the samre problem with mine Alt conversion.

I cleaned all conections and made sure there was a solid ground and all was

fixed.

The ground to the alternator? Could you show me a pic?

On the 280 everything wires right back to the same sopts on the alt. Just take a wire brush and clean all the connections so they have good contact. The black wire is your ground so make sure that one is clean.

Try checking your Amp Gauge. I just had this problem wing my 240 and forund the gauge bad. Bypassed the gauge, for now, and charge the battery at a constant 14.5V.

Thanks for all the replies!

I took the car to a local shop. After they had looked her over well, they told me they think the ground from the alt has some breakage in it somewhere and they're in the process of locating it.

They said the rest of the wiring looked pretty good, so now it's just a process of finding the break and making a new one.

I do hope with the correct voltage that I'll get the correct fuel pressure as well.