driveability troubleshooting help request

[TDS-94SSEi]

Hey All,

So, the latest development with the Bonneville, it's running quite poorly. But not setting off any fault codes, so I'm not sure what to make of the symptoms.

Car starts fine, idles smooth, revs nicely under no load. No strange noises.

Whne driving, I have found that the car will hesitate and stutter under acceleration, if it is done aggressively. If I slowly roll into the throttle, I will notice a slight surge/miss is what it feels like. At cruising highway speed, the stutter will occur again if I encounter a decent grade that puts extra load on it. I have noticed that the sysmtoms are MUCH more severe if I am in Overdrive, and the RPMS are lower. The same grade, for example, in Regular Drive will produce much less stuttering. But it still doesn't feel "right". I have not kept my foot in it when the stutter occurs, for it feels too violent, and I'm afraid I might do some damage.

I have not spent a lot of time yet doing any troubleshooting, feeling kind of lost without a Service Engine code to start with. My first thought was fuel delivery. Or maybe ignition coils. Or something in the transmission, because even though it feels like it shifts correct when driving, the way it reacts is as if it were in the wrong gear. I noticed that my console buttons that used to swap between "normal' and 'performance' shift are both dark now, I think they used to work, but it's been a while since I've been driving this car now. I did notice this problem occasionally last fall when I was driving the car. My wife has been behind the wheel for the last couple months, and now that I have had the chance to drive it myself, it has become a bigger problem and occurs with regularity now, I have found.

The battery cables and connections there are clean and solid, had that taken care of last fall. And when those were giving me trouble, I never had any symptoms like what I am stricken with now.

Anyone have any guidance, suggestions where I should start looking? I do NOT own a code scanner that will talk with this car, I believe that my pure OBD-II pocket scanner has the wrong cable end. But like I said, even though there is OBVIOUSLY something wrong, there has been nothing that has set the Service Engine light yet.

Thanks for reading, I look forward to any help/ideas you can share.

[KM AXer]

Based on a few of the symptoms, I'm thinking that these might be factors:
Fuel flow/pressure.... Either a clogged filter, or a weak pump, or injectors which are not frunctioning correctly. At lower fuel delivery levels, such as idle, the issue apparently is not present, but it crops up when fuel demand is increased.
Throttle Position Sensor.... Part of the system which determines how much fuel should be delivered via injection.
Mass Air Flow Sensor.... The tiny wire reads changes in resistance which is dependent on the air which flows over it. On my FI cars, cleaning the MAF is one of the first things I do if some runability issue crops up. Note that specialty tools may be required to get it out of the intake tubing, and that there is a specific spray cleaner made just for that purpose, as others can damage the unit.

[Bob Dillon]

Either a clogged filter,

Word.

$15 for the part an 10 minutes to change it. Do so and get back to us.

[J Wikoff]

I've never really had a clogged filter, but that is acting a lot like when my fuel pump was dying.

[TDS-94SSEi]

Thanks for sharing your ideas everyone. I will try and see if I can spend some time on it this weekend, and start with a fuel filter. Maybe see what kind of fuel pressure I might be getting. I would think that if I were having any issues with a sensor of MAF, that it would probably throw a code, no? I was going to try and tap on the MAF and see if it had any effect, as a quick check.

I wouldn't be too surprised if my pump was on it's way out. I've put about 70,000 + on the car, and it had about 75,000 when I acquired it, and I've not touched anything fuel-related in my time with it. That's a pretty good run I would think. But starting with a filter sure is a cheap first step. . . .

Will report back once I finally have some time to wrench!

[RJolly87]

You can also unplug the maf sensor. The car will run without it, using estimation based on throttle input and oxygen sensor. The car will not be happy during this, but if it runs crappy in a completely different way, without the original problem,it gives you a place to start.

[kemicala]

ive had similar problems..also replace the pcv valve. cheap, easy and just might fix that problem.

[TDS-94SSEi]

Have not had a chance to do anything yet, but went to start the car and move it out of the garage, and right now it barely idels, just severe chugg-chugg. Throttle application makes it worse, so I shut it off and have been driving the old truck until I have some time to troubleshoot more. Would agree that a PCV valve is eay and cheap too, and likely overdue for a replacement anyway. May pick one of those up too when I hit the parts store.

[Jrs3800]

Replace the fuel filter and check the fuel pressure... sounds a lot like a lack of fuel...