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Sorting out no-start problem


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15 replies to this topic

#1 Nug

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Posted 19 November 2003 - 10:46 AM

Does anyone have pics of ecu's with identification?
The ecu I have has four connectors, each a different size. The ecu that came with the engine, and was not used, has three connectors.

I NEED a positive ID on the ecu I have. It is SUPPOSED to be the one I need.

#2 Nug

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Posted 19 November 2003 - 10:49 AM

Or did I grab the TCU out of the donor car?

#3 Legacy777

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Posted 19 November 2003 - 11:43 AM

ECU has four connectors, TCU has three.

I've mentioned this page before, but people seem to forget

http://www.main.expe...cans/FSM_Scans/

it has all the pinout info you want. ECU & TCU.....was taken from the 1990 FSM's.

I'm also assuming you've seen this pic, which shows the physical location of each....the ECU & TCU
http://www.main.expe...ges/ecuhide.jpg

#4 Legacy777

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Posted 19 November 2003 - 11:44 AM

I also would like to know what connections you have hooked up. IE what pins did you hook up and what did you not hook up from the original wiring harness?

#5 Nug

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Posted 19 November 2003 - 06:35 PM

Terminal 4 on the F47 block isn't hooked up. There isn't even mention of it that I can find in the FSM. It's a yellow/green wire. The only other things that aren't hooked up include the gauges, vehicle speed sensor, and the check engine light.

I put it in check mode today, and it cycled the fuel pump. The check engine light wire was hooked to my voltmeter, but it doesn't react quickly enough to determine the number of blinks. Does that light need to be a LED?

I also checked the resistance on the ignition coil. It appears to have the continuity of a brick.

If the coil is dead, does the computer keep the fuel pump off so fuel isn't unnecessarily injected into the engine? That's my new theory.

I didn't even think about the fact that the automatic car has a TCU. Now I feel dumb.

#6 Nug

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Posted 19 November 2003 - 11:02 PM

Ok, this is what I've got. I definately have crank and cam sensor inputs going into the computer, verified with voltmeter. I also managed to test the ignition coil wrong, but finally got that right and it's fine. The ignitor circuit is done correctly, and is grounded properly.

The fuel pump definately is not running while cranking. It comes on with the key momentarily. Test modes on the computer work, it cycles the fuel pump, and it tries to spit out codes, which I can't read for the lack of a CEL.

Checking for ignition output at the computer yeilded some odd results. With the ignitor plugged in, the FSM says to backprobe it and look for voltage pulsations which is the computer telling the ignition coil to fire. With the ignition on, I get around 5 volts. Cranking, it drops to zero. Is this the fault of the ignitor, or ecu? I didn't think to check it with the ignitor unplugged to try to isolate it, cuz the FSM never mentioned that. It said after that check, if abnormal results are found, to replace the ignitor. But that still doesn't explain the fuel pump not coming on while cranking, unless the computer is looking for the correct ignition signal. I don't know. Anyone got a used ecu sitting around they wanna sell?

#7 Legacy777

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Posted 20 November 2003 - 10:44 AM

the info I have on the fuel pump control goes like this

flow chart

Crank angle sensor => ECU => Fuel Pump Relay => Fuel Pump

If that's the case, then the ignitor shouldn't affect the fuel pump....

#8 Legacy777

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Posted 20 November 2003 - 10:48 AM

other option you could try is just hard wiring the fuel pump relay to ground and a switch, so you can turn the fuel pump on & off on your own.

#9 1 Lucky Texan

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Posted 20 November 2003 - 12:17 PM

Is there a fuel cut-off like when you have a wreck that could be an issue here? I mean, what tells the ECU you had a wreck so it can cut-off the fuel? maybe the airbag system or something?

just a guess

#10 Nug

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Posted 20 November 2003 - 01:30 PM

The signal to the ignition system is screwed up, too. There is five volts with ignition on, and nothing while cranking.

#11 Nug

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Posted 20 November 2003 - 01:32 PM

Texan,
If that was the case, it isn't anymore. I disassembled the entire harness and streamlined it to include only things to make the engine run.

#12 1 Lucky Texan

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Posted 20 November 2003 - 06:34 PM

Where's the current drop during cranking? You may have a cable about to break or some under sized wiring. The fuel pump is probably off during cranking because the voltage drops too much. maybe the starter or battery is bad? Sneak path to ground?

#13 Nug

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Posted 20 November 2003 - 07:17 PM

I have double 0 battery cables on it, and the battery is brand new. EVERYTHING is brand new. Except the engine and sensors.
I might have a few problems, but this afternoon I came to the conclusion there is no spark because of the ignitor.

#14 Nug

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Posted 20 November 2003 - 10:37 PM

I'm getting another ECU and ignitor to just 'see' what happens.

#15 1 Lucky Texan

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Posted 20 November 2003 - 11:11 PM

I know you'll get it running, I'm just brainstorming here. I guess the voltage actually powering the ECU stays good during cranking - the SIGNAL out to the ign. is what drops? If so I misunderstood the other post.

good luck - I bet you're close.

#16 Nug

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Posted 21 November 2003 - 07:49 AM

Exactly. When i disconnected the ignitor, though, I got a voltage pulsation from the computer, which the FSM says is the signal for the coil to fire. So I am looking for an ignitor.




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