4.0 starting trouble... timing chain issues?

skyysipper · 05-27-2007, 01:20 AM

Hi all,

Driving along the curvy 152 highway cutting over to the 5 to Los Angeles, my water pump gave out and broke the belt. I decided to take the belt off and try to get to the nearest parts shop (10 miles away) and started driving... After about 5 minutes, I heard a pop and the engine gave out and we coasted to a stop. Ended up getting my stock 96 grand cherokee (242k miles) towed home and replaced the water pump and belt, but now NO START!!L@Q%.

So, fuel and spark are there, cranks fine but no start. Low compression (~30psi) on all cylinders (wet and dry test no change), so i'm thinking the timing chain?

Any thoughts, suggestions?... Already prepped down to the timing cover I'm about to remove the gears and chain tomorrow...

twojeeps · 05-27-2007, 02:54 AM

If the chain snapped or jumped you should be getting a trouble code because the cam will not match the crank timing anymore. And you may not be getting spark if that's the case. Turn the ignition off and on 3 times and look at the code flashing on the check engine light.

I'd bet that the chain is fine. But, 5 miles without a water pump is enough to do serious damage. I'd do a compression check to see if anything got seriously screwed.
EDIT: Never mind, you did a compression check. But the timing chains are pretty reliable - My money is still on something else, but check the codes anyway.

skyysipper · 05-27-2007, 01:20 PM

Does that ignition on/off three times work with a 96 (obd 2)? Also, what damage could have come from driving without a water pump unless it over heated, right? I was watching the temperature pretty closely and it didn't go any where near redline temperature...

twojeeps · 05-27-2007, 02:57 PM

Quote:

Originally Posted by skyysipper

Does that ignition on/off three times work with a 96 (obd 2)? Also, what damage could have come from driving without a water pump unless it over heated, right? I was watching the temperature pretty closely and it didn't go any where near redline temperature...

I've read it will work on all ZJ's except '98. I could be wrong, and if so, it might be a good idea to pick up an OBD2 scan tool.

The problem with the gauge is that this is just the temperature at the sending unit itself. Without the water flowing, the temperature you read is not going to accurately represent temperatures in critical areas like the water jackets in the head and block, which could have been dangerously high.

skyysipper · 05-27-2007, 03:13 PM

Wouldn't it then be the head gasket if it overheated, and would that cause low compression on all cylinders?

twojeeps · 05-27-2007, 03:40 PM

Head gasket, cracked head/block, burned valves, etc. Though I will agree that the results of the compression test do suggest incorrect valve timing, but it's hard for me to imagine how overheating could cause a timing chain to jump, unless the 4.0 uses a nylon timing gear (does it? I would hope not!) or the overheating baked a cam bearing and caused the camshaft to seize or bind in the block (which a timing chain won't fix.) Did you check the trouble codes?

Regardless, it's easy enough to check for incorrect valve timing by turning the engine to TDC on cylinder #1 and pulling the distributor cap. If the rotor is not pointed toward #1 plug wire, you've got a problem.

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05-27-2007, 01:20 AM	#1
skyysipper Registered Join Date: May 2007 Posts: 29 Thanks: 0 Thanked 0 Times in 0 Posts	4.0 starting trouble... timing chain issues? Hi all, Driving along the curvy 152 highway cutting over to the 5 to Los Angeles, my water pump gave out and broke the belt. I decided to take the belt off and try to get to the nearest parts shop (10 miles away) and started driving... After about 5 minutes, I heard a pop and the engine gave out and we coasted to a stop. Ended up getting my stock 96 grand cherokee (242k miles) towed home and replaced the water pump and belt, but now NO START!!L@Q%. So, fuel and spark are there, cranks fine but no start. Low compression (~30psi) on all cylinders (wet and dry test no change), so i'm thinking the timing chain? Any thoughts, suggestions?... Already prepped down to the timing cover I'm about to remove the gears and chain tomorrow...

05-27-2007, 02:54 AM	#2
twojeeps Registered Join Date: Jul 2006 Posts: 2,223 Thanks: 2 Thanked 8 Times in 8 Posts	If the chain snapped or jumped you should be getting a trouble code because the cam will not match the crank timing anymore. And you may not be getting spark if that's the case. Turn the ignition off and on 3 times and look at the code flashing on the check engine light. I'd bet that the chain is fine. But, 5 miles without a water pump is enough to do serious damage. I'd do a compression check to see if anything got seriously screwed. EDIT: Never mind, you did a compression check. But the timing chains are pretty reliable - My money is still on something else, but check the codes anyway.

05-27-2007, 01:20 PM	#3
skyysipper Registered Join Date: May 2007 Posts: 29 Thanks: 0 Thanked 0 Times in 0 Posts	Does that ignition on/off three times work with a 96 (obd 2)? Also, what damage could have come from driving without a water pump unless it over heated, right? I was watching the temperature pretty closely and it didn't go any where near redline temperature...

05-27-2007, 03:13 PM	#5
skyysipper Registered Join Date: May 2007 Posts: 29 Thanks: 0 Thanked 0 Times in 0 Posts	Wouldn't it then be the head gasket if it overheated, and would that cause low compression on all cylinders?

05-27-2007, 03:40 PM	#6
twojeeps Registered Join Date: Jul 2006 Posts: 2,223 Thanks: 2 Thanked 8 Times in 8 Posts	Head gasket, cracked head/block, burned valves, etc. Though I will agree that the results of the compression test do suggest incorrect valve timing, but it's hard for me to imagine how overheating could cause a timing chain to jump, unless the 4.0 uses a nylon timing gear (does it? I would hope not!) or the overheating baked a cam bearing and caused the camshaft to seize or bind in the block (which a timing chain won't fix.) Did you check the trouble codes? Regardless, it's easy enough to check for incorrect valve timing by turning the engine to TDC on cylinder #1 and pulling the distributor cap. If the rotor is not pointed toward #1 plug wire, you've got a problem.