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Old 08-21-2007, 10:42 PM   #1
elliotl
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Cool Testing for bad ECU, &/or bad Fuel Pump

Here's the short story:
My Supra won't fire - it turns forever but won't fire. I'm fairly convinced that it's the fuel pump but I was also wondering if my ECU might be fried. In short, my alternator died - I was wondering if the alternator & battery dying could possibly hurt either the pump or the ECU. However I did get it to run a few times while the alternator was still dead just running purely off the (brand new) battery, so if the dying alternator did damage, it wasn't total. I did a diagnosis check as per TSRM, and I got the "healthy" steady blink code back like nothing was wrong.

I actually tried to purposely trick the ECU to report something faulty by removing relays (such as fuel pump replay), removing fuses, unplugging different components, etc. and it always blinked back the healthy code. Could this mean my ECU is faulty, and it's therefore not powering the pump or injectors? Or would the ECU not find errors in such things?
After replacing plugs, wires, distributor cap + rotor, air filter, alternator, and belts it's still not starting, however it's getting spark.
For full details, read on...


Unecessarily long story!
My 1986.5 Supra one day wouldn't start - it worked a couple hours before, but then it would just turn without firing. The plugs looked really bad and the wires just as bad so I replaced them. I also replaced the battery because it was 5yrs old. I also cleaned the PCV tube. It still wouldn't start. All fuses were fine, so I cleaned out a few random electrical plugs such as the fuel pump relay and some others, and that was about it. Tried it again and it fired right up.

That night I drove it about 10 miles, started it 3 times just fine, and the following morning it started up just fine to get me to work. I then drove it literally only across the street for lunch, turned it off, and 15 minutes later tried starting it with no luck - it's been in the parking lot for 3 days now. Now, I noticed both the brake light & battery light were always on for that brief 12 hour span that it ran, which I found meant the alternator was shot. So I took the alternator and had it tested, indeed dead, and put a new one in the car. Also changed the distributor cap & rotor, air filter and drive belts - still won't start.

Tested spark - sparks just fine. Seems to be no vacuum leaks. Sprayed starter fluid into the intake manifold - car burns it up on a dime so that tells me it's igniting but not getting fuel.

I checked for diganosis codes as shown in the TSRM, but I just got the "healthy" steady blink. When I put the key to on, I hear a noise for a second of what I'd guess is the fuel pump. I pulled the EFI fuse and listened for it again and heard nothing. (which would further point to the noise being the pump). But I also (with the EFI fuse back in of course) had a friend get near the gas inlet and open it with his ear to it, and he said he heard nothing at all... so I'm confused on this point. Now back at home I am second guessing him...maybe I should be the one to listen for it! I also bridged terminals +B and Fp as discussed here: http://www.cygnusx1.net/Supra/Librar...aspx?S=FI&P=71
and the fuel pump relay on the left side of the engine compartment made a buzzing noise. Is this the "fuel return noise" as stated in the manual? Would the actual pump be running when those terminals are linked, and should I do the ear-to-gastank test while +B & Fp are bridged?

Now, I'm wondering if it's possible that the alternator dying could have damaged the ECU, to explain the lack of error codes and it not controlling the EFI system correctly. Likely I'm just telling myself this because I don't want to tow it to a mechanic and pay for the pump replacement!

Also probably of importance:
I've had an issue on and off the last 4-6 months, where very rarely (maybe 4 separate occasions in this period) the car would not idle without depressing the gas pedal. Sometimes this would magically fix itself as I was driving, other times it would do that until I stopped driving it. Again, this only happened a few brief times in half a year and I never thought much of it. Is this signs of a failing fuel pump?

Any further ideas, or should I just break down and get the pump replaced?
Thanks,
Elliot
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