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We have Engo 10k Synthetic IN STOCK!!! Hurry while supplieCustom Axle Work at CCORJEEP Gear Change Packages From ROCKRIDGE 4WD. We Are DIFF

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Unread 11-16-2006, 03:08 PM   #1
myriad360
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2001 XJ Cherokee 
 
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ECU problem

'88 Jeep Cherokee 4.0L. I am looking at schematics after having a starting / running problem, and the schematics say that B7 at the ECU connector and Pin 5 at the Diag. Connector under the hood should be battery positive, but they are ohming 0 to ground! I was wondering where this contact originally is suppose connect to the positive battery terminal, so I can track it down. Anyone?

Thanks.

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Unread 11-16-2006, 08:41 PM   #2
coppertop71
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Are you using the schematic from the renix maual? Page 53-54 show the power latch replay and a wire to Dia connector D-2 pin 5

Its hard to see but it looks like B7 get power from a possible fusable link wire from the battery likely the starter relay (page 40) or more likely though the ignition switch and also delivers power to the latch relay. Check for power at positionor wire 30 on the power latch relay and trace in reverse from there.

The schematic I'm looking at show a number for the wire coming from the battery but it is unreadable might be D5 or D15. I might even be wrong all together because the B7 pin number is hard to read too but it does show Batt at the connection for the ECU.

The power latch relay operates the the idle speed sensor.
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Unread 11-17-2006, 11:23 AM   #3
myriad360
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Yeah, I checked that out, my copy is pretty blurry too. I believe that it comes from the start relay, although it is pretty hard to trace from the conduit coming from the computer starting right under the cooling liquid resovior to the starter relay. After cleaning some contacts under the dash yesterday, B7, and D5 under the hood, are measuring 12 V. I can't put my fingure on why, all of the wires look like they are in fairly good condition (and I did get to see them all, unfortunatly). It is possible that I may have measured incorrectly previously, but seems rather unprobable. So the situation is now that we have spark to the spark plugs, we have perfect fuel pressure, but we have no signal to the (practically new) injectors. A Chiltons told me to measure the resistance across the injector harness leads. Should be about 5 ohms on every injector. It is 6 ohms, which I wouldn't think would be too big of a deal, but the Chiltons told me that if it was not exactly 5 ohms, then there was a problem. If it was more, then test with a DRB II tool (I am getting sick of hearing about that thing ), and that the ECU is probably bad.

So I am looking for a new ECU today. I am concerned however about why this one has burned out, if that is the case. Is there a place online that sells them? I am not sure where to begin with trying to find out why this one is burned out. I may have a dealership do it if they cover replacement should the new one burn out, although I am sure that is quite expensive.

Is there a place online one could recommend for ECU's?

Thanks.
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Unread 11-17-2006, 12:59 PM   #4
ORJ
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Wrecking yard. Cheap and if it doesn't work you can take it back once or twice for replacements. Electrical items are non-refundable. If you get a new or rebuilt one and want a replacement, you better be able to explain your testing path and conclusion to show how it is bad. The wrecking yard folks usually give you another one because they don't know if it is good or bad.

If you get a used one and it does exactly the same thing, it is probably going to be something else - that is my experience.

If I remember correctly, you initially replaced the ignition switch and everything snowballed from there. I would plug a different one in to test it's effect. Maybe you've already eliminated it from the equation?
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Unread 11-17-2006, 01:27 PM   #5
myriad360
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Quote:
Originally Posted by ORJ
Wrecking yard. Cheap and if it doesn't work you can take it back once or twice for replacements. Electrical items are non-refundable. If you get a new or rebuilt one and want a replacement, you better be able to explain your testing path and conclusion to show how it is bad. The wrecking yard folks usually give you another one because they don't know if it is good or bad.

If you get a used one and it does exactly the same thing, it is probably going to be something else - that is my experience.

If I remember correctly, you initially replaced the ignition switch and everything snowballed from there. I would plug a different one in to test it's effect. Maybe you've already eliminated it from the equation?
Yeah, we replaced the ignition switch with a brand new one. Still same problem. Today we got a pretty good looking ECU for an auto salvage, it was sitting in their parts room, not in the yard. Still same problem, so my main concern right now is why the injectors are not getting signal? The interesting thing about this ECU is that it does measure 5 ohms across the injector harness leads to the ECU. So what sensors /etc tell the ECU to not send the injectors a signal? We have tested most of the sonsors, definatly all of the ones that could tell the engine to shut off.

Very strange.

Thanks.
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Unread 11-17-2006, 02:25 PM   #6
myriad360
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Engine Check light

Anyone know if / where the check engine light is?
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