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sprinkles08
sprinkles08, ASE Certified Technician
Category: Jeep
Satisfied Customers: 21604
Experience:  Chrysler/Dodge/Jeep Master Certified, ASE Master and Advanced Certified, Trans and Hybrid Specialist
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Grand Cherokee limited: I have a 1996 ZJ. The security light

Customer Question

I have a 1996 ZJ. The security light is steady lot on the top of my dash pad. No spark or fuel and no communication from the computer. I drove it for 40 mins into town and then this happened when I went to return home 30 mins later. Only the driver door was opened to get out and then back in. It ran perfect before I shut it off. I did find that the #6 fuse on the interior panel was blown and did continue to blow when replaced. It does not blow any more after 4 and a power probe was used but truck will still not start. There does not seem to be a security module on the passenger side but I believe all security runs thru the body control module in the dash on driver side. I have the whole dash pulled apart and have replaced door switches key cylinder and ignition switch also cps. Dunno where to go next.
Submitted: 1 year ago.
Category: Jeep
Expert:  sprinkles08 replied 1 year ago.
Hello and welcome to JustAnswer! The powertrain control module is down. It may be down due to a loss of power or ground, a short to voltage on a sensor ground circuit, a short to ground on a reference voltage circuit, or the failure could be internal in the PCM. Odds are the problem is internal in the PCM and it will need to be replaced. What will need to be done is load test it's powers and grounds as well as check for shorts on the circuits I mentioned. These shorts could be internally shorted sensors or wiring issues. The crank sensor is the most common one to short internally but if it has been replaced that's obviously not the issue. If the powers and grounds are good and the sensor ground/reference circuits aren't shorted then the PCM can be condemned.
Customer: replied 1 year ago.
I have already done all that. I'm just looking for a direct corrilation to the interior #6 fuse being blown and tripping the powerprobe. If I can trace that circuit I will more than likely find the culprit. It seems I have an odd year for this model. It's hard to find ant good schematics and locations of the modules. The number 6 fuse is for the security module. Where is it located if not behind the glove box? Is it in fact integrated with the body control module.
Expert:  sprinkles08 replied 1 year ago.
Fuse 6 blowing isn't related to the no start condition. It's a power feed to the vehicle information center, park/neutral switch for the reverse lamps, the daytime running lamp and speed proportional steering modules if equipped.you don't have a VTSS module, VTSS is controlled by the BCM on a 1996.
Customer: replied 1 year ago.
So even with the blown fuse the engine should still run. Is it at all possible to disable the bcm? If I get a used bcm from the junk yard will it need some sort of programming or reset? Will it just automatically work when plugged in? It's really hard to find a computer used. I have a 3 plug set up and most other jeeps in a 4 year spread have a single connector. What is so different with my jeep that it does not have the same style computer?
Expert:  sprinkles08 replied 1 year ago.
Fuse 6 in the junction block being blown will not cause the PCM to be non responsive. The BCM will not need to be replaced. A replacement PCM will need to have the VIN and mileage programmed but it will start and run. The part number would need to match exactly. The SBEC style PCM with a single connector was phased out, the three connector JTEC replaced it and was used in the late 90's.
Customer: replied 1 year ago.
It is my understanding that the jtec computer cannot be programmed or modified for performance and there are few companies that have made computers to run a performance 5.9 in a jeep. This may govern my in tensions to keep it fuel injected. I was told the crossover intake manifold to put a carburetor on is expensive. I'm researching all available options. I'm a old school mopar enthusiast but this jeep has got me beat. Looks like the pcm may be the culprit.
Expert:  sprinkles08 replied 1 year ago.
The PCM controls cruise control, charging, a/c and transmission functions as well as the engine so keep in mind trying to make all systems work properly without a PCM will be quite a bit more extensive than just converting to a carburetor and modifying the ignition system.
Customer: replied 1 year ago.
I would rather fix the issue at hand but I am looking to build a performance engine and I would like to keep it injected. Do you know off hand how to upgrade the existing electrical system or if there is an option to program the stock computer? I heard once apon a time there was a mopar performance computer that was programed for the jeeps but they are all bit obsolete these days. I have a local automotive electrical specialist and I plan to trailer the jeep there tomorrow. He will most likely tell me exactly what my problem is. I have 400$ invested in random parts at this point. I know when to quit and pay the man. He has extensive equipment and knowlege. After a week of troubleshooting I think I have reached my limit. When you turn wrenches for a living there comes a point where working on your own shit just isn't an option.
Expert:  sprinkles08 replied 1 year ago.
When modifying a fuel injected engine it would take custom programming based on the actual modifications for it to run correctly. Cam specs, injector flow rate, etc would need to be taken into account and custom software would need to be written and flashed into it.
Customer: replied 1 year ago.
I was told the computer I have cannot be flashed with a custom program. Is there any truth to that? If it's not true do you know who does make custom tunes and flashes them?
Expert:  sprinkles08 replied 1 year ago.
The only way to make it run correctly with engine modifications would be custom software.
I haven't had any direct experience with any companies doing custom programming. You may be able to find a shop in your area able to do it or you may have to send yours out to a company and let them know what modifications have been done. Here is one company that does JTEC programming:
http://bgperformance.com/tuning-magnum-truck.aspx