Shuddering on acceleration.

[aedwards]

Hope someone can help with some info:
We have a 32R Infinity, with a w22workhorse chassis. Before storing the unit we
Replaced plugs and wires, had oil changed to Mobil one and had the trans serviced. I added stabeizer and filled the tank. We left n.j. Last week for Florida and that's when we experienced the engine shuttering. All wires are tight and scanned with no codes. So would the fuel filter cause something like this? It has bed 20000 miles since it was changed.
Thank you in advance for any help.
Al Edwards

[jesilvas]

It could be the fuel filter or the fuel itself.

[TonyDi]

You could have picked up a load of bad gas, water or dirt in it. If it was tuned up correctly my next step would be to replace the fuel filters.

[HeapBigEngin]

It could very well be a filter issue.....and a change could resolve it. If not, consider a couple of other possibilites. Does the shuddering feel like an engine miss?. Does the shudder occur on initial acceleration, but seem to diminish at cruising speed? Does the engine shudder or miss when "revving' it up a bit in neutral? Can you feel the shudder through the gas pedal....or does it seem to come up through the floor?
Prior to changing the filter (which may need to be replaced anyhow), suggest you double check that the new plug wires are installed securely at the plugs AND that the correct wire goes to the correct plug. A couple of "crossed" plug wires will result in a miss or shudder under load....but it may not be quite noticeable when just revving the engine in neutral. And it may also seem to diminish at cruising speed. You'll need to know the engine "firing order" to do this correctly. Not hard, just takes a bit of time and dilligence.

Hopefully your situation is a filter change or a wire routing issue. I had another thought re the transmission service you mentioned....but I won't go there with my thoughts just yet. Please let us know what you discover...thanks!!

[aedwards]

Thanks for getting back.
When I start the engine it kicks right over but runs a little rough, push down a little on the gas peddle and it smooths out. At highway speeds it shutters going up even slight grades and smooths out on level highway, it can still be noticed only slightly. I do not feel it in the gas peddle. Also the passing gear kicks in a little more then usual.
I am going to replace the fuel filter anyway. The reason I started looking at fuel is because we got no codes at all and all plug wires are tight.
Thank you,
Al Edwards

[CJBROWN]

Sure sounds like a misfire underload. Time to go thru those plugs and wires again.

I have also heard of people getting bad fuel but this sounds more like ignition. If it was more intermittent then that would point more toward fuel. The filter certainly could have gelled (phase separated) fuel, so worth throwing one on there for $10 or whatever they are now. Since the last thing done was plugs and wires that would be where I would be looking.

[TonyDi]

I agree with CJBROWN recheck the plugs and wires. Also make sure the timing is correct. If it's easy to do, I'd pull the plugs and check them for gap and whether or not they're fouled. It doesn't take much to screw up a plug.

[CJBROWN]

Yes, run it hard, shut down, pull plugs. You'll be able to see if they are firing or not - are they tan or black?

I'll never forget having the same issue with ours. It would start and run fine but every time we hit a freeway on ramp where I'd mash the throttle it would stutter and shimmy. I was so sure it was fuel related I went as far as insulating the fuel lines for vapor lock, and identifying a source for a new fuel pump. Dropping the tank is the only thing that kept me from replacing that $200 fuel pump. I was close. I replaced that little fuel filter too - I even cut open the old one and low and behold it was virtually spotless.

Somebody here said 'PLUG WIRES' and I said 'NO WAY' because I had just replaced them with taylor race wires - if they were good enough for a race car certainly they would hold up on my motorhome.

Sure enough, there was at least one burnt plug boot. The instructions that come with the wires state that the 1500 degree boots on the wires don't need the factory metal heat shields so they were installed without. And they burnt.

I went through a lot of machinations for a simple plug wire replacement. Motor ran like a top afterward. And I still have some really nice insulated fuel lines coming up the chassis.

[HeapBigEngin]

A follow up to my original post regarding plug wires....

The additional info you posted makes it sound even more like an electrical issue. If your coach did NOT exhibit any of these issues before your servicing, then it is likely to be something that flared up AFTER your servicing. Make sense?

Suggest, again, to check that the proper wires go to the correct plug....it is easier than you think to mess that up.....believe me. Like others have said, check the boots as well. Also, when you pull the plugs, examine them VERY carefully for outside cracks to the porcelian. It is MUCH easier to crack a plug's porcelian than many think....especially if one is working in tight places. A little torque with a socket or an extension on the plug on an angle is all that is required. The slightest crack will cause a miss like you describe. You will need to get an inexpensive magnifying glass to be really sure....the naked eye may not spot it. This takes time....but it is one of the things you need to eliminate before you get much further.

Have chased too many "ghost" misses in the past caused by both of the issues I mentioned above. Frequently these gremlins are caused by simple things that we sometimes overlook or don't consider. Eliminate these before throwing parts at it, IMHO. Hope this helps....

Hang in there....you will find it. And thanks for getting back to us.

[aedwards]

Thanks everyone:
After pressing really hard on every plug wire, the last one and hardest one to get to, drivers side rear plug popper on. So even the pros at the shop that replaced everything did not push it hard enough. Running great.
Thanks again:
Al Edwards

[HeapBigEngin]

Originally Posted by aedwards

Thanks everyone:
After pressing really hard on every plug wire, the last one and hardest one to get to, drivers side rear plug popper on. So even the pros at the shop that replaced everything did not push it hard enough. Running great.
Thanks again:
Al Edwards

Outstanding!! Glad to hear it was something so simple....oftentimes it turns out that way. But too many times we discover that AFTER we have thrown parts, time and $'s at an issue.....please don't ask me why I am all too familiar with that process!!

Again, great news. And thanks for keeping us "posted" on your progress.

[CJBROWN]

Did you pay for a happy ending?

[TAN]

When mine did that it was a bad plug wire. Of course I paid $1200.00 to have the fuel pump changed first just to find out it was a plug wire.