550sx

Suddenly my car won't start.
the symptoms I noticed are
the reference wire(grey) is reading about 7.5 volts not 5(blue wire is now reading a little over 1 when closed , had it set to about .71).
and the brown wire going to ignition coil is getting no power when attempting to start car. I tested the MSD(white wire to ground to trigger coil wire ) and it is working so it seems
that the distributor is not signalling the ignition properly,
noticed 12 volts on the white wire(ignition on) from distributor to MSD as well, don't remember if that is supposed to be happening.


got a 87 gta tpi harness rewired for the 7730 ecm,
installed in 240sx,
my car is for 30 miles away where I have been building it
so i only get out there every couple of weeks.
last time I was there the engine fired up and ran.
This time the battery was dead, so I charged it with my car.
noticed I was getting 19 volts during charging(not sure if this is bad, had only registerd about 13-14 when doing this prior).
I also wrapped up some of the harness in corrugated tubing near where it comes through the fender, harness makes a sharp bend at this point and is covered by aluminum plate to protect from tires(plate presses on the harness due to space issues).

all sensors are brand new, new distributor from jegs, using GP1 from moates.net, MSD 6btm with adapter harness for tpi., checked all the fuses,
ran last time I was out there to work on it.

I am new to cars in general, this is my first build.
Started as a carb'd motor and had it driving and had to redo
the engine swap adding the tpi top end , harness, smog equipment and new exhaust to get it street legal.
please forgive me if I am missing something that seems obvious.

I am trying to figure out if a the ecm is bad or not.
I am assuming that if I have somehow caused the grey tps reference wire to connect to another with 12 volts I would see 12 volts on the grey wire as well.
I figure if was just the ignition control module in the distributor then I would not have the high voltage on tps.

any ideas?
thanks in advance

550sx

figured it out,
the brand new ignition control module in jegs distributor I bought stopped working,
put in the old one from the original distributor and it fired right up.

had an extra terminal for the ecm connectors so I put it in place of the
tps reference(5v) pin a5 so I could eliminate the possibility of exposed wires touching or and causing the volts to be higher,
got 6.4 approximately today right out of the ecm(1 foot of wire),
same reading on map reference (5v) pin A4,
is this normal to have the volts that much higher than?
car seemed to be running ok, no driving(car on jacks) but in neutral it idled allright, part throttle , and acceleration were what I expected from the current tune.

Is there something wrong with ecm if it is putting out more than 5 volts on a pin that should only have 5volts?

RBob

iTrader: (1)

May be a grounding issue. Make sure that all EFI system grounds are only to the engine block. The ECM case is already grounded via the design, so that is to be isolated from any chassis/body grounds.

To see if it is the ECM that is bad, pop the one or two terminals out of the +5 V reference opening(s). Plug the connector(s) back in and key-on, engine-off. Measure from the pin to the ECM case. If still over 5 volts then it is the ECM.

RBob.

550sx

thank you,

sorry if this seems obvious but why would the EFI system grounds need to be isolated?
I don't think I can isolate mine because, I am using solid engine mounts with universal sbc mounts welded to frame rails, the battery is connected to engine block for starter and to the chassis as well,engine bay is stitch welded, and frame rails are welded solid where front clip meets the cab.the bolts holding my ecm case are touching metal that is connected t chassis.

I did check on 5v terminals yesterday as you described. I used a spare terminal wired in instead of the one going to map(7730 pin a4) and tps(7730 pin a5) reference pins, checked each individually and got over 6 Volts on both.
so this means the ecm is bad.


strange thing is the ecm seems to be working, car turned on idled , part throttle , I expected I would see more problems, maybe if I looked at a data stream I would see the increase in map voltages in the system thinking it has more pressure than there actually is, probably the same with tps if I open more than part way, i get over 5 volts when tps fully open, once is reaches the voltage that it expects to be WOT it would not register any change after that.


I guess that charging the car at over 17volts( my camry is putting out 17-18 volts when I connect the 2 to charge) for 20-30 minutes and connecting the battery disconnect so that the high voltage goes through the system is a bad idea .
probably fried the ignition control module and the ECM together.

RBob

iTrader: (1)

> sorry if this seems obvious but why would the EFI system grounds need to be isolated?

They aren't isolated, all of the EFI harness grounds go to the engine block.

The ECM case should not be grounded locally. It is already grounded via the EFI harness. Further grounding of it produces ground loops. IOW, current will used the EFI ground wires between the block and ECM case grounds for other then EFI system use.

The rest of your grounding is OK.

I also recommend some vibration isolation for the ECM .

RBob.

550sx

got it thanks,

will move all the efi harness grounds to the engine block,

ecm is mounted from metal that has some flex so it will dampen some of the vibration, also using rubber washers between case and where mounting.

thank you,