TySoCal

Dead stock 95 SC300 with 160K on the odo. The short story is that the fuel pump runs okay when cranking, so engine starts, but fuel pump shuts off as soon as you let go of the key, so engine dies.

I'm not much of an engine mechanic but I'm quite comfortable with electrical troubleshooting of all sorts. So I'm pretty confident the following details are accurate.

Turn on ignition, all expected lights in the cluster except for the CEL come on (CEL should be on). Normal sounds of IAC and trac sub throttle motors "finding home" are heard. EFI relay clicks on, Pin A1 (IGSW) of ECM connector goes to +12 as it should. The CEL bulb is fine: jumpering W to E1 on the interior DLC makes it light up. From this I conclude fuses and ignition switch are okay.

Crank engine, FP output of ECM comes on (4.8 volts), fuel pump runs and pumps plenty of fuel, engine starts.

Let off key and FP output of ECM immediately goes to 0v so fuel pump stops and engine immediately dies. This pretty well shows me fuel pump ECU and fuel pump itself are okay, It is definitely the ECM telling the fuel pump ECU to stop - why?? That is the question...

If I jumper B+ to FP on the DLC under the hood (essentially a temporary "12 volt mod", the fuel pump runs full speed and fuel is heard circulating in the rail.

With the fuel pump jumpered on as above, the car starts runs and drives completely fine!

Jumpering TE1 to E1 (to try and pull codes) does NOT work - the CEL and O/D Off lights don't even come on much less flash anything.

And finally... sometimes - not always - if I leave the car overnight with battery disconnected, in the morning it will be normal: CEL comes on as expected, car starts and drives with no fuel pump jumper, and if I try to pull codes the CEL and O/D flash constantly as expected for "no codes".

I am at my wits end with this thing... Help??

mrmj2u

iTrader: (2)

I had a very similar problem. Quickest test is to replace the ECU.

Replacing the ECU fixed my issue.

TySoCal

Yeah... that's pretty much what I was thinking of doing next but was hoping there might be a less costly solution!

TySoCal

Yup. Swapped my ECM with one from a wrecking yard today. Suddenly everything is fine. Time will tell but it looks like my problem is solved.

mrmj2u

iTrader: (2)

Excellent! I'm glad the computer got your car running again.

TySoCal

One last thing to wrap up the thread...

Once I got the car running I decided to take a look inside the old ECM. The capacitors and board looked fine, no leaking, no corrosion, no bulging, nothing. So I replaced all 7 electrolytic caps anyway. I mean what the heck, the thing's broken anyway, it costs less than 5 bucks for the whole set of high class Chemicon PW(M) Series EDIT: Nichicon UPW series "high reliability low ESR" capacitors from a reputable U.S. distributor (no fakes allowed!), and it's an easy repair assuming you have the right tools (which I do). So I re-capped it, plugged it back into the car and to my great surprise it works perfectly now. Guess I'll leave it in service, re-cap the one from the wrecking yard since it's equally old, and either try to sell it or keep it as a spare.

So I guess the moral to the story is that just because old caps look good does not necessarily mean that they actually are good!