99 grand cherokee no start

[giorno71]

So im trying to help my friend get his 99 grand Cherokee limited 4.7l going. Ran perfect when he parked it in the spring and this is the first time he tried starting it, battery was completely dead, he put a booster pack on it but he put it on backwards for about a second, then disconnected it right away, never turned it over. now when you turn the key on but not turn it over it takes about 30 seconds before the check engine light comes on and he cant remember if it was always that way. I was thinking he fried the ecu but the light is coming on just not right away. only fuse blown was the junction buss power. just wondering if anyone else thinks the ecu is fried and if so is there an easy way to determine if it is or not.   Thanks

[jkrubi]

Have you tried starting it since? What else have you tried besides for hooking the battery up backwards, anything?
Cel comes on after it does a self test, some are faster the others

[giorno71]

we tried a fully charged battery and checked fuses but haven't really got into it yet, was mainly worried about the computer being toast after what he told me he did. gonna start checking all the basic stuff this week. but thanks  was always under the impression that the cel light came on as soon as you turn the key but then again iv been driving a 94 yj since 97 as my daily driver lol guess im just used to my old no frills rig. thanks again

[cLAY]

Does it turn over when you turn the key to the start position?

[giorno71]

haven't gotten back to it since my last post gonna try to get at it tomorrow, yep it turns over, can hear the fuel pump, gauges all seem to work except the fuel gauge, and the economy readout says 0 km to empty both worked before being parked. it has fuel, had half a tank when parked and added $20.00 more just to be sure because the gauge not working now. my buddy found a dead mouse in it, all I can think now is chewed wires...

[cLAY]

I would try to check and see if it's got any codes.  Some cry products can display codes in the odometer display by cycling g the key 3 times. Not sure if a '99 has that capability or not.  Otherwise find or buy a scanner and check the codes. If you can communicate with the ecm then it's probably ok.

[giorno71]

yep hooked a scanner up to it and it said no codes stored so it is reading the ecu but the battery has been dead for so long the codes were probably erased. it does have to odometer code display but its not doing anything when I do the 3 key on and off but that might also b because it has no codes stored.

[jkrubi]

When you get to it, try giving it a shot of ether, see if it will start and run for a sec.  If not start with the basics-spark,fuel,air. And go from there.
I've had issues starting cars/trucks that have sat for a bit, and once it was running even for a second, it seems to remember what it is suppose to do and eventually it started and ran.

[giorno71]

well it fired up tonight, 90% sure its the transponder in the key or the receiver. was rust turning the key off and on taking note what the warning lights were doing when on a turn the all lit up the way I thought they should and vroom started up,  shut it off and it went back to no start and the key with the line through it light stayed on.  so anyone know how to bypass that system?