Stumble on deceleration after tune-up

Tugela

Well-known member
May 21, 2007
4,754
562
Seattle
Time to check the VSS.


Replaced the VSS. No change. Cleaned IACV. It had some carbon buildup. No change. No signs of vacuum leaks.



I must have messed up the timing somehow. It still idles okay, but under throttle is when it stumbles and bucks and has no power. I'm almost done eliminating possibilities.
 

Tugela

Well-known member
May 21, 2007
4,754
562
Seattle
Air intake hose is the accordion rubber/plastic one. I did set timing using an inductive timing light, however I just realized that I set timing at idle, not at 2,000rpm. Perhaps that explains why the idle is fine and higher revs is where the stumbling appears.
 

Tugela

Well-known member
May 21, 2007
4,754
562
Seattle
Fuel filter is new.


I had a long chat with PT Schram yesterday (what other kind is there?) running through all the things I've done to address the stumbling. He was at a loss to explain what the cause could be. Without seeing it in person, his best guess was clogged cats. That theory matches with the gradual onset and worsening of the problem, the fact that it idles okay but struggles under throttle.



Before I start messing with the exhaust system I need to double check a couple other things to eliminate all the remaining engine-related possibilities, but PT's hypothesis is an interesting one. Is there any way to inspect the cats? They don't rattle - I had a broken one on my Disco and none of the sounds from that are present on the Range Rover.
 

robertf

Well-known member
Jan 22, 2006
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maybe some kind of air fitting into the o2 bung with pressure gauge and see if theres a pressure difference between the two sides.
 

Tugela

Well-known member
May 21, 2007
4,754
562
Seattle
maybe some kind of air fitting into the o2 bung with pressure gauge and see if theres a pressure difference between the two sides.


Interesting idea. I think I only have upstream O2 sensors. I do need to replace the entire exhaust behind the Y-pipe so maybe I should just do the whole shebang...but first more elimination of options.
 

Blueboy

Well-known member
Apr 20, 2004
3,205
459
Back in the USA; Rockwood, PA
Yes, only 2 upstream O2 sensors.

I went with a SS NRP system and never regreted it.

On the 109 I had with a 3.9 V8, ran it without cats.

The engine really ran better yet of course it was reg as a 1967.

Good luck!
 

Tugela

Well-known member
May 21, 2007
4,754
562
Seattle
Issue resolved. It was the ignition coil.


I took the RRC to a local specialist who conducted a thorough diagnosis, most of which was encouraging.


Compression is good.
Vacuum is good.
Seals are good.
Timing was at -4 degrees, reset to -6 degrees.
My engine is in great shape.



The problem was that the Pertronix ignition coil that I installed wasn't getting along well with the other components. I had not thought to check this because it was brand new, but looking back it was the only thing I hadn't checked.


Lessons learned (or reinforced):
1. when you're replacing a lot of parts on your truck, do one at a time and test each after installation to make sure everything works as it should. It's harder to isolate a mistake or faulty/incompatible part when you change several things at once.
2. Pertronix ignition coils may not be the best match for the Lucas ignition system.
 

Tugela

Well-known member
May 21, 2007
4,754
562
Seattle
I went with Lucas, for a few reasons.


1. The relatively new Bosch coil I have was on the shelf of my garage, 16 miles from the shop.
2. The replacement Lucas was $60 and that's what the shop recommended. They only work on Rovers, I've had good experience with them before, so I trusted their choice.

3. I wanted to ride my bike to the shop and drive home in the truck. Getting it towed back to my house so I could swap the part was not worth the negligible cost savings.
4. Having a spare coil is not a bad idea.


I have driven about 18 miles since collecting the Rangie from the shop. So far no sign of the stumble but I'll need more miles in a wider range of driving conditions to be convinced that this fix worked.
 

Blueboy

Well-known member
Apr 20, 2004
3,205
459
Back in the USA; Rockwood, PA
Great to hear all turned out well.

Over the years I've tried "updating" items on mine and in general the results aren't that good.

Basically at this point I try to only use OEM or as close as I can get.

My last starting or lack thereof problem also was resolved with a new coil.