Community Forums

deputydog · 03-26-2008, 03:46 PM

My recently aquired Allegro Bay has a skip or miss at lower rpms under load. I've read all the posts about the plug wires so I changed them just to see, but the miss is still there. It seems more noticable for the first few miles, but continues even after several hours of driving. 60mph in overdrive (5 speed
Allison when you hit a small incline is where I see it most.

I'm thinking about buying two coils and keep moving them about to see if that has any effect. It does not show any codes, but I do see knock retard of 5? to 15? at times, but not necessarily coinciding with the miss.

I tried high test gas for two tanks plus Chevron Techron injector cleaner and it didn't seem to help.

The coach was low mileage when I got it (a 2005 with 2,950 miles) so I thought an injector might be dirty.

Any ideas?? or anyone know if there is a good way to test a coil?

Thanks-

deputydog · 03-26-2008, 03:46 PM

My recently aquired Allegro Bay has a skip or miss at lower rpms under load. I've read all the posts about the plug wires so I changed them just to see, but the miss is still there. It seems more noticable for the first few miles, but continues even after several hours of driving. 60mph in overdrive (5 speed
Allison when you hit a small incline is where I see it most.

I'm thinking about buying two coils and keep moving them about to see if that has any effect. It does not show any codes, but I do see knock retard of 5? to 15? at times, but not necessarily coinciding with the miss.

I tried high test gas for two tanks plus Chevron Techron injector cleaner and it didn't seem to help.

The coach was low mileage when I got it (a 2005 with 2,950 miles) so I thought an injector might be dirty.

Any ideas?? or anyone know if there is a good way to test a coil?

Thanks-

DriVer · 03-26-2008, 05:48 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by deputydog:
Any ideas?? or anyone know if there is a good way to test a coil? </div></BLOCKQUOTE>That can be tested with a Tech II. Perhaps you can run up to Turning Wheel in Ocala and have them diagnose your rig with theirs. No need to continue to spend money to resolve a problem when you don't exactly know what the problem is. You may also want to take your rig to the Allison shop to see if there is a problem with the transmission. Rule out what isn't broke and only choose to fix the things that might need fixin'.

RottenRalph · 03-26-2008, 06:00 PM

I had the same symptoms. Turned out to be the back right spark plug. It looked like it was coated in ash.

This was determined after a 5 minute computer scan. Well worth the $42 scan fee.

babock · 03-27-2008, 07:40 AM

I agree with RottenRalph. I was able to diagnose a faulty spark plug with my OBDII scan. There was a miss on multiple cylinders detected with more on one cylinder than the other. Turned out that the ceramic on one sparkplug had a tiny chip out of it.

deputydog · 03-29-2008, 06:41 AM

I was bored so I pulled the plugs to see how they looked. They all looked good with normal deposits, but when I wiped them off good I found one on the right side that had a cracked ceramic all the way from the base to the top. Hopefully that was the problem. We shall see.

Max Hubrich · 03-29-2008, 09:36 AM

I don't think the 8.1 has fuel injectors-- it's throttle body injection. At least mine is-- I think

When the wires are replaced it's a good idea to do plugs at the same time.

Tom N · 03-29-2008, 12:08 PM

THe VOrtec 8.1 uses Sequential Port Fuel Injection with an injector for each cylinder.

-Tom

deputydog · 03-30-2008, 01:50 PM

Problem solved!! The cracked plug must have been it. We took a 50 or so mile ride today and not one miss/skip. I'm a happy camper now! (if only we were camping)

Regarding Max's post, about doing wires and plugs at the same time, I would agree, but at 2,900 miles on platinum plugs it did not cross my mind.

Not sure what cracked it - no visible damage, just a hairline crack from the top all the way to the base. Must have been arcing to the base, but no carbon tracking that I could see.