I have a 1998 Range Rover with a Gems 4.0 that I purchased a while back. When I purchased the vehicle I was told that the oil pump had went out, but it should run. Before I purchased it I started it and turned it right back off. After that I put it on a trailer and drug it home. Now it's sitting in my garage and I'm stuck. I have pulled the front of the motor off three times now and I'm a little desperate for help.

When I pulled this apart the first time I replaced the oil pump, and noticed the timing chain was pretty loose (stretched) so I replaced the chain and the sprockets, lined up the crankshaft and camshaft marks to the 6 o'clock and 12 0'clock position. After I got this all back together I turned the ignition over, the truck turns over just fine but it would not start. While trying to start the truck it sounded like it was super close to starting and it kept backfiring into the airbox. I gave up for the night and consulted with a couple friends with more engine skills than myself and we all felt like it had to do with timing because of how it was backfiring into the air box. We decided the next step should be to pull it all back apart, pull the chain off, rotate the crankshaft (lower gear) one full rotation, align the timing marks again and see if that fixes it. We put it all back together, turned it over and same thing. It sounds like it really wants to start but it just won't quite get there. This time it's not backfiring (popping like it did) but it still seems to be exhausting through the air box. I have it all pulled apart again and before I put this back together I'm wondering what others think. It takes me allot of time pulling this all apart and putting it back together so I'm hoping to figure something out before I put it back together hopefully for the last time . My gut feeling is that I'm still not on top dead center when I put the chain back on. Does anybody have any other thoughts of what this could be or know where to look for how to get this engine back to top dead center.

Thank You so much for any help or advice.
Derek

 

The workshop manuals are in the google drive linked in my signature. Have at it.

I don’t have first hand experience but I do recall threads about oil pump replacements so a search of the message board in the D1 section may be productive

 

Sounds like the engine is not timed properly and you have exhaust valve(s) that are opening at the wrong time

 

Can you post a photo of the gears and chain assembled with the timing marks aligned? As I recall it can be easy to skip a tooth.
Another thought: If gas is old you might need new gas.
If you really want to be sure of the crank and cam timing, you could remove the valve cover for #1 cylinder (left side) to see the position of the intake and exhaust valves as you travel 4 strokes. The exhaust valve is moved by the front rocker. The timing marks on the gears should align at the top of the power stroke.

 

The Vehicle has been sitting for quite a while. I'm not sure how long it sat before I purchased it, but I had not thought of that. Do you think that would cause it to backfire through the air box? I'm also attaching a picture of the marks on the timing chain. The last time I took it apart I put mechanics paint on the tooth with the mark just to make sure I was getting it right if your wondering why the paint marks.

 

D1 manual diagram for timing mark alignment
Utah,
Let's think it through. The backfire into the filter box means ignition is happening when an intake valve is open. There are two main choices. Timing is way off (for example 360 degrees, like you tried already), or spark plug wires got crossed (OK the third choice is both at the same time). Bad gas could make it difficult to start, then cylinders are getting washed down with liquid gas, then gas spits into the exhaust system and all bets are off. There are about 67 degrees of valve overlap (both open at the same time), so during this time ignition in the exhaust system could back flow through the filter box.

So in the position shown in your fuzzy photo, both intake and exhaust valves should be closed (i.e. valves up position, push rods down position). My Disco uses the same gears, nice.

Are you going to look under the valve cover? Then you could install the chain (re-check the marks) and turn the crank with a wrench to verify the valves are sequencing correctly, very roughly first half turn is power stroke (both valves closed), second half turn is exhaust (exhaust valve open), third half turn is intake (intake valve is open), fourth is compression (both valves are closed again) back to TDC. (The shop manual gives the exact valve angles.) Then double check your spark plug wires go to the correct cylinders. Get rid of the old gas, and fire it up. Good luck!

PS. Notice in the diagram that the timing marks are in between the gear points, especially on the crank gear.