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Discussion Starter · #1 ·
‘97 D1 4.0, GEMS, 175k.

Briefly: New head gaskets. Have fuel, starter’s good, have spark. No start. Pop on first crank, then nothing. Did not touch timing case.

Ran fine, but had overheating issues when pointed uphill and was leaking all over, so did the head gaskets. Heads were a bit warped, but not too much. Clear signs of coolant leaks on old gaskets. Had heads machined to get them flat; don’t know if they’d been done before. Got it all back together, but the injectors weren’t sealing. So pulled the intake again and replaced with new Mustang yellow injectors.

Still no start. Starter motor goes hard. There’s pressure in the fuel rail. Spark light tester shows spark (new Champion plugs). But all I get is a small bang/pop on the first crank and nothing else. There’s a slight bunt smell afterwards from the motor. I didn’t remove the timing case. I did rotate the crankshaft with the heads off to clean the piston heads, but that shouldn’t matter on a pushrod, right?

Button on the passenger firewall is depressed. Fuses for each firing system are good. I haven’t swapped the ignition module because I’m not sure where it is (and my laptop with the Rave manual downloaded is offsite). The wiring harness was a mess (especially everything that hung below the valve covers), so I cleaned it up a lot with brake cleaner. Battery is weak at the moment, putting my 500 crank amp jump pack on it doesn’t help.

I have not done a compression test. Planning to tomorrow.

Replaced a number of accessories and components at the same time (steering box, cores-out radiator flush, power and ground cables to starter and chassis, solenoid ground, ac compressor, thermostat, all rubber vacuum lines, heater core, heck even fenders, the hood, headlights, rekeyed the ignition cylinder - too much). I also cleaned the engine bay, engine, and undercarriage throughly when the heads were off. It was all super gross. I wrapped the top of the block with a tarp to keep water out and removed any remaining electrical components from the engine bay, but I don’t know if water might’ve damaged something.

Need this thing running - new job and new child. This Disco needs to get in the rotation.


Something to consider: I’ve got a ‘96 D1 GEMS that runs just fine (more or less). So I can yank parts off that and plug them into the ‘97 for troubleshooting.


Questions:
Could the crank or cam sensors be bad but the ECU still allow spark?
What should I pull off the running truck to try on this one?
I don’t know if these heads had been skimmed before - how much material would need to be taken off before the pistons slap the valves?
What am I doing wrong?!?


Thoughts and suggestions are much appreciated.

Cheers
 

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Sounds to me like you have bent some push rods. You will have to remove valve covers to access the push rods and remove them. One at a time. Then you can see what is going on. If the heads were planed too much, you may have the piston hitting the valves, which would also cause the pushrods to bend.

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Also, if the piston hit the valve and bent the rods (rods too long) you could buy some shorter rods. I have had zero luck in shortening push rods over the years. If you have a small inspection camera, pull out the spark plugs and push little camera through the hole and check piston tops. If there is mechanical damage to the piston, you will see it. If there is mechanical damage, you will have to remove the cylindrical heads and check the condition of the valve as they may be broken or bent as well.
Sound like you are going to have a bit of a project on you hands with this one.

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I say whoa cowboy 🤠 Don’t overthink it!
Keep it simple and figure out what you’re missing before throwing parts at it
What do yo need to run…..
Spark
Fuel
Pressure (compression)
Verify them all
If any one is missing the others can’t make it run.
Once you have tested all 3 you should know what you are missing
As for cam and crank sensors- only crank sensor is monitored during cranking and starting so if you have spark then that’s not the missing link BUT what about firing order????? How sure are you that you have all ignition leads in the correct position on the coil packs?
Pushrod length is a possibility but a lot would need to come off the heads and proper fix is shimming the rocker shafts NOT shorter pushrods. Would likely be more of an issue that the valves are not able to close than bending pushrods as this is a non interference engine design.
Not a full answer but hopefully it will help to get you back on track to isolating the issue
Please report back with what you find
 

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Discussion Starter · #5 · (Edited)
EDIT: Dumb dumb dumb. Just realize I didn’t rotate the crank between cylinder tests. Man. Gotta stop doing this stuff in the middle of the night…

Uh oh.

Compression test complete : super low on two; no compression on another.

Sequence:
(Cylinder - psi)

1 - 120
3 - 30
5 - 95
7 - 95

2 - 120
4 - 120
6 - 0-15
8 - 115

So both banks are affected. What is that about? Went out to get a new test gauge just to be sure. Have done this job on a 4.0 before just fine. But man, something is afoul today.

I put a precision straight edge on the block before assembling. No gaps. I’ve used this machine shop before with success. I put a wrench on the exposed head bolts and they’re all just as torqued as they outta be. I can see and feel that the gaskets are actually in place (in the event I somehow overlooked laying down gaskets on BOTH sides before installing heads). What on earth is this about…?

Anything else you all suggest before tearing the whole lot down again? I’ll pop the passenger valve cover off to see if the rods are trashed next I suppose…


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Discussion Starter · #6 ·
Went ahead and pulled a valve cover and pushrods are all a-okay. (Well, a couple of them are off by a bit - when rolling down a 20” table, they run maybe 4 degrees astray. But like, is that “bent”?)

Also: double/triple/quadruple(?) checked connecting keys, loose wiring, plug and coil connections in the last few days. And I have used this Mustang “upgrade” on another 4.0 with success. But sure well hoping it was the injectors. Compression matter has me flummoxed.

Threw a socket on exposed head bolts and they’re damned tight. Thinking maybe the cam/crank timing and valve position is the matter… but again, thought the nature of a pushrod architecture would force valves to be in step… Does that make sense?


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Went ahead and pulled a valve cover and pushrods are all a-okay. (Well, a couple of them are off by a bit - when rolling down a 20” table, they run maybe 4 degrees astray. But like, is that “bent”?)

Also: double/triple/quadruple(?) checked connecting keys, loose wiring, plug and coil connections in the last few days. And I have used this Mustang “upgrade” on another 4.0 with success. But sure well hoping it was the injectors. Compression matter has me flummoxed.

Threw a socket on exposed head bolts and they’re damned tight. Thinking maybe the cam/crank timing and valve position is the matter… but again, thought the nature of a pushrod architecture would force valves to be in step… Does that make sense?


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Is there a chance you put the head gasket on upside down? I have seen this on other engines and it has affected the operation of the engine. Not sure if the 4.0 has that issue.
Also, the low compression numbers are very concerning to me. Sound like some valves may not be closing or are broken.
Have not looked yet, but are the intake and exhaust push rods the same length? Did you mix them up when reinstalling them?

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