Unusual rough running problem
 

Last Friday filled up (w/93 octane) at a Chevron station where I frequently buy my gasoline. Drove home (about 8 miles) and parked the car overnight. Didn't drive it again until Sunday morning to make the run for the newspaper. Car stumbled/shuddered pretty bad. Thought maybe I got a load of bad gas, so since then I have put in a bottle of Techron and 2 qts of toluene. Running better but not right. Here's what it's like today....

Once up to speed, and on flat ground (like there's any other kind around here), the car runs fine, don't feel any engine misfires. When at about 1/3 to 2/3 throttle there is some stumbling. When at WOT, there is sometimes a surging sensation - where it changes from full-strength acceleration to something less- still relatively smooth, but down on power.

Does this during "first run of the morning" cold to fully warmed up - but cold is a bit worse.

Just filled up on my way home today with Shell V-Power. Only drove about a mile to the house, and it's parked until I go to work tomorrow.

Interestingly, I normally get about 19.8 mpg. I drive a pretty standard route to/from work up & down Hiway A1A. The mpg for this tank while suffering the performance issue - 24.2 mpg!? It wasn't babied either, I accelerated harder than normal to avoid running in the middle throttle position and getting all that misfire.

No check engine light, no hard starting. Haven't yet checked anything except battery ground.

So, :confused:

Lee,
given that when you put in the techron and toluene it ran better and you're experiencing surging, I'd take a look at the injectors and/or the fuel filter.
-Bill

All 6?
 

Are you sure it is hitting on all six cyl? Mine was somewhat like that and one of the coils was bad.

Lee

Assuming my wife gives me some time this weekend ;) I'll start checking.

I have been assuming it was fuel related since it did get better with the cleaner additions. The fuel filter is only about 10K miles old (like that means anything) - but since it actually runs better under WOT, which would mean highest flow rate, I'm doubting the filter.

I wonder about a bad sparkplugs/coil, again since it gets better under WOT - but then I always learn new things - can they behave in this way? Plugs are Bosch-4, about 25K miles old.

Idle is fine, more or less OK at WOT, poor at mid-throttle. Note, this is throttle induced and is not speed sensitive, I can get the shuddering/misfire if at 15 or 50 mph. Also noted today that if I give enough gas to cause it to start, then back off a little, then give a little more (past where it would have been an issue) it seems to work OK. Using this self-induced kind of surge - press, slight release, press some more, repeat - I can almost totally avoid the issue.

I'd begin by checking the TPS. If it's o.k. try disconnecting the EGR valve and drive to see if the problem remains. If it goes away let me know.

Argh!
 

I have also been having this problem off and on for just about a year now. I have been watching over that great period of time for any number of consistant circumstances, but have found almost none. It may go away for weeks, and then come back full force, sputtering popping and shuddering that it takes forever to attain 40mph. When I took it to a mechanic to just get analyzed, he said it was the number 3 or 5 cylinder (second and third from you on the passenger side whilst facing the car). I guess it made total sense, being that if the rubber "insulation" around the coil pack was bad that it would ground somewhere and cause that cylinder to misfire. But if this was the case...then wouldnt it be persistant? And also, (and maybe its like a placebo effect) it seems like sometimes when i fill up after being empty that it gets worse for a little while, but there is really no telling b/c its so random (also I just changed the fuel filter less than 2k ago, or at least Chike did it for me...haha)

-Andrew R.

Pitch us some help here!

C'mon now!
 

Anyone have advice to help us "rough runners"?

what spark plugs do you use? I had a problem(s) in my legacy with using bosch spark plugs of several varieties. esp the +4s. of course my leg was turbo so things are a little different (esp given the issues with part-throttle-full-boost) but I'd maintain that bad sparks could be your problem. I recommend NGK v-powers. they have served me well in all he cars I use. at the very least, checking plugs could help figure out what else could be wrong. of course checking the plugs is as much of a pain as the hesitation itself in these cars.

here's the thread:

http://bbs.legacycentral.org/viewtopic.php?t=514

read the first post and the bottom post of the first page for my reactions to changing the plugs. FWIW

it may sound stupid, but have you check your air filter????

Water
 

Could you possibly have water in a coil pack or something? My car did this around a 2 months ago after it floated down my street for a couple of feet. It acted up until I drove it for an hour straight on the freeway, apparently it dried out as I have had no problem since. Just a thought.

Steve

A+++++++++++

I finally got around to trying today on my way to work. It's not that I've been lazy, we ripped out all the interior walls and ceiling over the weekend. I got the ceilling back and some of the walls...lots of work left over from the hurricane season still yet to go.

Anyway, I pulled off the line from the EGR vac controller to the EGR valve. Seemed no different with the vac line hanging loose.

Good - I'm not certain how the EGR is ported to eaach cylinder in the SVX but on some cars there are individual ports that can clog. Here's how their problem manifests: if you have a six cylinder engine imagine what would happen if three or four of those ports were to clog up. The excess EGR flow is pushed into the remaining two or three ports, causing misfires of varying degree on those cylinders. This only happens when the EGR opens, which is at above idle speed when the engine is warm. The problem is less noticeable at higher engine speed and throttle opening. Since there would be flow there wouldn't be an EGR code. That is why I wanted you to pull the hose off. A quick, easy check.

You might take a peak at the MAF to see if it has collected some oil or garbage. A quick spritz with some carb clean (on the sensor wire inside the air tube) may be the cure. Be gentle, they are frail. Remember at around 80% to wide open throttle (WOT) the MAF isn't used and isn't a part of the picture.

Good as in how exactly? :D J/K, and thanks - as always

I've seen the trick used on Honda Accords (tapping a hole into the port plug and pulling it so the passages can be cleaned), but doubt it will be that easy to check on the SVX...guess I'll find out.

If there was no difference with it unplugged I wouldn't bother checking the ports. Check out the MAF next.