Stumble on deceleration after tune-up

p m

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Callsign: AK6PM
Apr 19, 2004
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La Jolla, CA
www.3rj.org
I don't know if base idle adjustment is ever warranted on these trucks. A PO of my latest LWB dicked with it, and it occasionally hot-starts with 1500 rpm idle.
 

Tugela

Well-known member
May 21, 2007
3,927
4
Seattle
What are the chances that the problem could be caused by a faulty ignition amplifier? I read some past threads in this forum and found similar problems with that as the solution. Then I realized that my new distributor didn't come with a new ignition amplifier, so I reused the old one. Which could be the original from 1993 as far as I know. Atlantic British wants $72 for a new ignition amplifier, which is a little more than I want to spend on a guess.
 

Tugela

Well-known member
May 21, 2007
3,927
4
Seattle
The only other thing I can think of is maybe your speed transducer (VSS) is not working properly. WSM does not show a way of testing it though.
I found a good deal on a Lucas ignition amplifier and it's on the way. If that doesn't clear up the issue I'll look at the VSS. Thanks for the suggestion. Coincidentally I have one of those in my parts bin, too.
 

Tugela

Well-known member
May 21, 2007
3,927
4
Seattle
May I ask where as would like having a spare one of these.

Thanks!
Atlantic British was selling them for $37 through their ebay store. Same part number as the one on their website which was nearly double the price. Maybe I should get another.
 

Grenade

Well-known member
Oct 8, 2015
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Vegas
what did you do to resolve this?

Thanks!
Surprisingly I was able to find a TRUE Original OEM LUCAS rotor. Beefy as can be and all edges are rounded.

I still have a back up from the JY that is my emergency. Funny thing is I have the failed 4th unit on my desk as a reminder.
 

Grenade

Well-known member
Oct 8, 2015
86
0
Vegas
Atlantic British was selling them for $37 through their ebay store. Same part number as the one on their website which was nearly double the price. Maybe I should get another.
I've had two fail from AB. They warranted' both of them but that doesn't help when I'm on the road.
 

Tugela

Well-known member
May 21, 2007
3,927
4
Seattle
Update: finally got around to replacing the ignition amplifier module. Result? No improvement. My patience is wearing thin and I'm tempted to resort to professional help.
 

robertf

Well-known member
Jan 22, 2006
3,893
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Dallas
maybe check the TPS resistance for a smooth transition from open to close? If theres a problem with it when you let off the throttle maybe the ECU is interpreting it as a rapid pedal mash and dumping extra fuel just as the throttle is closing.
 

Tugela

Well-known member
May 21, 2007
3,927
4
Seattle
I've been considering throttle issues, however after replacing the ignition amplifier module now the stumble has gotten worse and the engine struggled on my brief test drive at 15 mph with a steady throttle. In an earlier experiment I turned the throttle cable tensioner a few rotations and that improved things, but that seems like a superficial solution.


I will say that after today's session mucking about with the distributor and getting the re-installation wrong the first time, I am more familiar with the subtle dance of TDC, timing, and finessing the distributor back into position. So it was valuable as a learning experience even if the outcome was not what I wante.