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Solve the impossible!!!!!!!

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Question From redrover on Solve the impossible!!!!!!!

Hi everyone,
I have a 1990 Land Rover Range Rover with 3.9L v8 in desprete need of help. While driving everything would act normal until I hit about 1900 RPM's. Then the engine would hesistate and want to stop working dropping to a almost stall and by some miracle coughing back to life before dying out and comming back again. It's reached the point it doesn't matter if i floor it or just let it sit because its putzing at everything. I replaced everything that would normally cause this problem: throttle position sensor, idle stepper motor, and have cleaned and sanded all electrical connectors from the battery, starter, coil and distributor and ignition cables. I also ran fuel injector cleaner thru the system because you never know. My thinking is that if i fix or try fixing everything all at the same time normal running will be achieved. Yet no forward progress has been made. I'm pretty sure that the problem is electrical but I've exhusted all my ideas. Any and all advice is needed.

Response From Tom Greenleaf

Just a direction to test out. Valve timing, vacuum leaks and exhaust restrictions. You've got some age on this pup so more comes into the mix than if newer. Good old testing with a vacuum gauge could be quite telling,


Response From redrover

thanks for a quick reply - ill be sure to try that and report back

Response From redrover

ok so heres the update. I did a bit more research and came to a few conclusions:
1) I have no idea what the proper vacuum pressure would be.
2)because of #1 I didn't check the vacuum system pressure.
3) my problems could be because of my distrubitor locking up. not entirely sure how this happens because it starts and drive. granted the hesitation and lost RPMs does point to fuel delivery something is telling me electrical still.

my source:
the faults they give(stepper motor, TPS etc,) are what were replaced to solve this problem

I have a new distributor cap and ignition wires on the way. Should be in by wednesday (4/8/2009) or hopefully sooner!

Response From Tom Greenleaf Top Rated Answer

Just a tidbit on engine "actual" vacuum and testing:

At sea level manifold vacuum at idle runs about 18ish Hg (inches of Mercury) or perhaps a tad higher. If you put a gauge in line such that a device is not disabled you get the real reading. It can tell of uniform low vacuum meaning usually valve timing, bouncing needle can suggest valve issues and floating needle can mean leaks. It's a pretty good old phart way to tell basic engine situation and can tell of exhaust restrictions.

The reading at idle should be steady and with no load when RPMs are held at 2,000 + RPMs the reading should be the same. If lower it suggests exhaust restriction but not why or where.

Vacuum is being monitored by everything and engine/trans functions adjust accordingly. Low vacuum suggests engine is under load and adjustment for extra fuel, timing adjustments and what gear an automatic should be in get involved,


Response From redrover

Where would be the best spot to hook the gauge up to? Wouldn't it give the same readings if i put a T-splitter in and hooked it up there?

Response From Tom Greenleaf

Items directly on intake or low on throttle body are frequently true manifold vacuum. So should the hose to a vacuum booster or pcv but would take larger "T" to adapt in line.

There are assorments of these type tees at parts or hardware stores,


Response From redrover

4/7 update
Last night i went to advance auto to rent the vacuum tester. I never acually took it out of the box because the truck wouldn't start, as in, when the key was turned to start everything died as if it shorted out, however, it never did. I got so pissed off at it I returned the kit. Later that night with help from Dad, we managed to get the engine turning over. I was forced to stop the process because there was severe arcing and sparking coming from the negative terminal on the battery.

Goals for today was to go back to advance and get a new terminal clamp and drill a new ground on the frame after inspecting the wire.

Good news: My distributor cap and ignition wires came today! too bad its snowing and the truck is stuck at the end of the driveway.

The guy at advance did tell me a way to check to see if there was a leak at the plenum chamber. When the engine is running spray carb cleaner in the chamber and around the outside of the vacuum hoses. If there is an idle fluxuation then there is a leak somewhere.

Hoping for warm weather again, and would love any/all thoughts on this.

Response From redrover

4/7 update 2:

I replaced the distributor cap and all of the ignition cables except for the one from the distributor to the coil, only because I couldn't slide the rubber boot easily and was excited. I took it for a spin and it hicupped twice going up my street. Other than that it was back to normal running conditions. Tomarrow I'll be replacing the old coil cable with the new one and it should be fine.

Thanks for the help. Ill be back soon enough with another problem.