marclub

I have a 96 SC400 that was running perfect until recently. No warning signs and didn't run bad before it decided to not start. It will turn over good with no battery or starter problems. Timing belt looks ok. I have tried to read all the articles on this site pertaining to no start. Most of the details seem to be for pre 96 models so it is a little difficult to follow exactly. I have done some tests and here is what I have found: No spark when tested (at spark plug and from coil) IGSW (Black/ orange wire) inlet at ECM and frame ground shows 12+ volts with key turned to run. B+ (black/red) and E1 (brown) both at ECM with key turned to run shows 12+ volts. However, I get less than 1 volt at E1 and frame ground at diagnostic port in engine bay with key turned to run. I have ran 12v directly to fuel pump just to test it and I can hear it working then, otherwise no FP sound when turning key.

I really don't know what else to check. I have a wire schematic of what I believe is a pre 96 model so I don't know if I'm doing this stuff correctly. Please HELP guys!

Ozzzzy

The most common faults that I have run up against with no start is the crank shaft or camshaft position sensors. Then leaking caps in your ECU.

marclub

Thank you for the reply. I checked the ECU for visible signs of any cap problems and everything looks fine. I know you can't always tell by looking but i don't know how to test it other than the doing voltage measurements I mentioned above. Do you test sensors you mentioned by resistance? If so, what should they be?

Ozzzzy

They are not that expensive. Just replace them and see. If not that, you can just return them.

marclub

Today I ran a couple of tests just to try something...Anything. I ran a wire direct ly from the battery to the fuel pump positive terminal behind the back seat. I heard the pump make a sound like it was working. I also heard a little sloshing sound in the tank? Does this mean that the fuel pump is working OK? So I tried to start the car while doing this and no go...nothing fired. Soo then I squirted some starter fluid into an air inlet that went to the intake and when I cranked the engine it fired a little It almost started.

I need some help from the experts on here.

I know I haven't tested or replaced the crank sensor as the previous response suggested. But what I want to know is: 1) How do I test the fuel pump to know for sure if it is good or bad?; 2) Why do I not get a spark when i test at the coil going to the plugs but it still tries to start when I supply fuel into the intake?; 3) If the fuel pump is good, what else would be keeping the fuel from getting to the injectors? (When I unscrewed a small screw at the top of what looks like to be the fuel pressure regulator at the fuel rail it was dry inside after running the 12v directly to FP and hearing the FP make noise). PLEASE HELP

marclub

Anyone there?. Need to give someone the credit for helping to get this SC running!

alltrac

Does the check engine light illuminate when the key is turned to the "on" position?

marclub

No. Computer may have died??

alltrac

No check engine light means that the computer hasn't been told to "turn on". Rough explanation of the starting circuit:

Key turned to on, 12V goes from battery to IGSW terminal on ECU (internal computer switching and voodoo occurs)
12V then goes OUT of the ECU through the MREL to the EFI MAIN Relay
EFI MAIN relay is then energized and sends 12V back to the ECU on +B (this turns the computer on)

It sounds like 12V is not coming from MREL terminal on the ECU to your EFI main relay.

Quick and easy test:

With KEY ON - remove EFI MAIN relay and reinstall. If you hear a few relays click and servo noise it will probably start. Sometimes this would make mine start. I never understood why it would work. It just did.

Find 12V constant with key off in your fuse box in the engine compartment or just use the positive battery terminal for super quick test. Run a jumper wire from the 12V constant to the +B on your check connector. Will probably hear a few servos spin up and some relays clicking. Turn the key on...check engine light....start it.

I had a similar issue with my car. and I ran it like this until I could get the ECU fixed. Just be sure to disconnect from the 12V source or it will drain the battery.

marclub

Ok. Tried the jumper from positive battery terminal to B+ on diagnostic connector in engine bay. I heard a click but only one and the car still didn't hit or fire or start. Checked resistance on crankshaft sensor and it was at 1100 Ohms cold so that looks good.

If I had a dead ECM would that jumper do any good? Do I assume that my ECM needs replaced? Is there any other tests I can do to confirm that before I wildly buy another computer??

alltrac

No check engine light with the key in the "on" position (assuming the light works) points to the EFI Main circuit and relay or the computer. If the EFI main circuit and relay test good, then the computer is a likely suspect. The computer can fail and do so many different things that can have you chasing things around. If you do get another computer, have yours rebuilt as another one will have problems down the road.

marclub

I will go that direction and locate an ECM. Do you recommend the rebuild services that are on Ebay? $150.

By the way...I did purchase the diodes and capacitors necessary to rebuilt the ECM per instructions I found on here. But when I looked at mine it looked fine ..no bulging caps or leaking spots. I think I could do the job but are there any tests I could do to confirm if the caps and/or diodes are bad? I would really not like to do all that and have something else wrong with the board!

alltrac

I sent mine to tanin auto for repair. I was 99% sure I had diagnosed the problem correctly on mine. Have you tried to pull the codes?

On my car, I was not getting a check engine light with the key in the "on" position. I started at the EFI main relay. During the fail condition the EFI Main relay was not getting enough voltage to engergize the relay. IGSW was getting 12V in, but MREL was not sending 12V out. I was able to bypass the EFI Main relay by giving +B 12V to make it run. That narrowed down the area to the internal workings of the ECU.

marclub

No codes. When i hook up scanner to port inside car in driver's left knee area under dash my scanner says something like "unable to communicate with ECM". As mentioned above, when I jumper positive battery to B+ and try to start the car nothing changes...no start...no fire. Should I check for 12V at ECM from B+?

I have no spark. I unscrewed the little screw in the top of what I think is the fuel pressure regulator (connected to the fuel rail on driver's side) and it is dry in there. So I don't think I am getting fuel either. There is fuel in the tank but the fuel pump does not come on when key is turned to "on" or "run".

I don't have wiring schematics for this year car so this is very difficult. ANYONE PLEASE feel free to jump in and help. (thank you for the help you have given') There is probably enough information in this thread for someone that knows these cars inside out to HELP. Again I don't mind getting another ECM but I would like to feel like I have done my homework. I just don't have the books to study!

marclub

OK. I had the ECM repaired and installed it and no change. STILL will not start. No voltage at B+ at diagnostic port in engine bay. Any suggestions? ANYONE??