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Stutter


Ranger

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Well I guess it's my turn. This afternoon I was on my way to work and as I was on the toll road entrance ramp I slowly accelerated from about 45 mph, not enough to downshift. I felt what I thought was a misfire. Somewhat like a coil breaking down under load. It still accelerated albeit slowly. When I got to work I put it in park and lightly brake torqued it and could not duplicate the symptoms. On the way home I tried it with a cold engine and all was normal. After normal operating temps were reached the same symptoms appeared. I thought maybe a weak fuel pump but WOT ran smooth though maybe not quite as much power. When cruising at 50 mph and a light throttle acceleration I can feel a pronounced stutter and hear an ocassional pop or bang. Hard to tell for sure if it is coming from the tail pipe or under the car but I swear I can feel something bumping the floor board. I can also feel this stutter or slip when accelerating normaly from a stop. I tried holding it steady and light brake pressure. No RPM jump. Once on a county back road with no traffic I stopped and brake torqued it again. This time I ran the RPM up to about 2000. At about 1600 I could feel an occasional stutter or slip again but I was standing still with my foot on the brake. I am starting to fear a transmission problem rather than an engine problem. Mayb this WOT stuff is not such a good idea after all. NO codes, temp normal 212f, no warning lights. What do you guys think?

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Larry,

I had similar symptoms on my '96 Seville a couple of months ago. It acted like it was losing fuel pressure. I checked the fuel pressure and it was normal. I misted the plug wires and there was no arcing. I pulled the front four plugs and three of the four plugs were missing the platinum pad on the ground electrode. I then removed the four rear plugs and three of the four plugs were missing the platinum pad on the ground electrode. The gap on the 6 plugs that were missing the platinum pads was .068-.070 and the spec. is .050.

I regapped the worn plugs to .050", re-installed them, test drove the car and it was fine. The next day, I installed a new set of AC 41-950 plugs.

Use an air impact wrench to break the plugs loose and you won't need to worry about damaging threads. I also retorqued the plugs after a day of driving.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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One other thing - when you disconnect the plug wire from the plug, use shop air to blow any crud from the cavity. Even though the boot seals against the cam cover, a little bit of dirt will ger by the seal.

I also re-torqued the plugs after a day of driving.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Well Kevin, you may be on to something here..... I hope. In the limited time I have before I have to get ready for work I was able to pull the front plugs and one of the rears. Most of the platinum tips were gone and the gaps were .060 or close. I cleaned them and regapped them. If that was the problem 5 out of 8 should make a difference and I'll replace them all ASAP. Looks like I'll have to remove the ignition module and coils to get at the last 3. The one thing I found though was that the manuals (owners and shop) both call for 41-900 plugs and I found 41-947's in there. ????

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I didn't have to remove the coils or module. I was able to access the rear plugs by unplugging the plug wire from the coil and that provided enough clearance for the socket and extension.

I will bet that all the drivability issues will be gone after you install new plugs.

The AC Delco website lists 41-950 as the plug for your car. I wonder why there is a descrepancy????

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Larry,

I pulled the front four plugs and three of the four plugs were missing the platinum pad on the ground electrode. I then removed the four rear plugs and three of the four plugs were missing the platinum pad on the ground electrode.

Use an air impact wrench to break the plugs loose and you won't need to worry about damaging threads. I also retorqued the plugs after a day of driving.

Hello People,

A question and a couple of comments.

What kind of plug is experiencing loss of the platinum pads? I recently had a set of Bosch that had one of the insulators break off. Luckily it was prevented from falling into the cylinder by the twin ground electrodes. I replaced them with AC plugs. The Bosch plugs were installed by the previous owner. I am a believer in AC plugs.

A word of caution on using an impact wrench on spark plugs. The impact nature of the wrench can crack the porcelin on spark plugs. I would NEVER :o reuse any spark plug that has been removed with an impact wrench. For that matter I wouldn't install a plug that has been dropped either. The plugs that have been subjected to any kind of impact can look just fine. They may even run OK for a time. But if a hairline crack has been started in the porcelin then the plug may fail at any time. With my luck it would fail when I was merging between two Mack trucks at 80 MPH on the Interstate. :blink:

Using air to blow out the spark plug recesses in the rocker covers is a great idea. Just be sure that you are wearing saafety glasses.

Have a great day.

Britt

Britt
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Ranger,

Looks like an easy fix there.

AC Delco 41-950 is the current spark plug number I believe. These numbers will change over time, so it is best to check for the latest reccommendation.

AC Delco Web Site

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Drive'em like you own 'em. - ....................04 DTS............................

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Well, the problem persists. On the way to work when leaving a stop light with light acceleration it felt like the tires were on patchy ice (slip, grab, slip, grab) which makes me think trans. When I am at cruise and I give it a little throttle I get a pretty bad studder or chuggle and if I lean on it just a bit more it gets worse and I hear and feel a pop or bang like a backfire, which makes me think ignition. If I get on it real hard it seems to smooth out. I am still unsure which direction to go in. I think I may just replace the plugs and see what happens from there. Any ideas are welcome as this one has me baffled.

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Well, the problem persists. On the way to work when leaving a stop light with light acceleration it felt like the tires were on patchy ice (slip, grab, slip, grab) which makes me think trans. When I am at cruise and I give it a little throttle I get a pretty bad studder or chuggle and if I lean on it just a bit more it gets worse and I hear and feel a pop or bang like a backfire, which makes me think ignition. If I get on it real hard it seems to smooth out. I am still unsure which direction to go in. I think I may just replace the plugs and see what happens from there. Any ideas are welcome as this one has me baffled.

Ranger, smell the tranny fluid and see if its burning. It certainly is giving confusing symptoms but like you said it initially seems to be a tranny problem with that patchy take off you described, but then the pop backfire confuses the problem... Odd... Try looking at the coils and the ignition wiring in the dark and maybe spritz them..., its sounding like a bad coil, but wouldnt you set a code from misfiring? I wonder if the traction control can cause this type of symptom?

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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Good idea on the trans fluid. I'll smell it when I get home tonight. Yes I would expect a code from a misfire. The lack of one and the feel from a standing start make me think trans, one of my worst fears (trans and head gaskets) but the popping and feel at cruise make it feel like ignition. It's really giving conflicting symptoms. Guru where are you?

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Good idea on the trans fluid. I'll smell it when I get home tonight. Yes I would expect a code from a misfire. The lack of one and the feel from a standing start make me think trans, one of my worst fears (trans and head gaskets) but the popping and feel at cruise make it feel like ignition. It's really giving conflicting symptoms. Guru where are you?

Don't jump to conclusion that it's the trans.... the engine must be misfiring really bad before the misfire code PC0300 sets. You only inspected 5 of the 8 plugs (and they were bad...) - my bet is that the remaining three are shot as well. When my Seville acted up per my earlier post, there were no codes set.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Kevin, you keep giving me a ray of hope, thank you. I do have a tendency to always think the worst. What really bothers me is that slipping feeling when accelerating from a dead stop. The engine does not feel or sound like it is missing at that point. The other thing that bothers me is that cleaning and regapping 5 out of 8 plugs did nothing to improve the situation. Gotta start some where so I guess plugs are the easiest. I'll get a set tomorrow and change them in a day or two.

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Larry,

I do not want to block the ray of hope Kevin and others give you, but what if you just put some Lukas stuff in the tranny and watch? It is not going to hurt anything right? And if nothing happens you can drain it later. I pray for your tranny.

Just my .02

The saddest thing in life is wasted talent

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Yeah, that thought had crossed my mind. I usually don't like to use additives but if it is the tranny then maybe it will buy me enough time to trade it. I wasn't looking to do that for a few more years but if it comes to a trans job I guess I'd rather put that money towards a newer car. Your prayers are appreciated.

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I just got home from work and noticed another symptom. I normaly run 1950 RPM @ 70 MPH. Tonight I was running about 200 RPM higher with minor fluctuations. Also I could not feel the normal TCC engagement at 41 MPH. I am starting to suspect the TCC.

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You only inspected 5 of the 8 plugs (and they were bad...) - my bet is that the remaining three are shot as well

It looks like failing platinum spark plugs are common. Are not regular plugs more predictable? At least their gap will not change drastically and unpredictably. My regular plugs worked fine for 13 years and 142.000 miles.

The saddest thing in life is wasted talent

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I just got home from work and noticed another symptom. I normaly run 1950 RPM @ 70 MPH. Tonight I was running about 200 RPM higher with minor fluctuations. Also I could not feel the normal TCC engagement at 41 MPH. I am starting to suspect the TCC.

Just some theoretical speculations: assuming one of your cylinders is out of loop. Does it mean the engine in the same gear should increase the RPM by 1/8 to keep the same speed (in this case70mph)? 200 rpm is close to 1950/8.

The saddest thing in life is wasted talent

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Adallac,

Your theory makes some sense. Every time I start to think I have it figured out, something or someone throws me in another direction. Keep the ideas coming, I need all the help I can get.

Northstar,

I have considered that as well. The plugs & wires have been untouched for 92K. The wires were just moved around for the fuel rail replacement, so that is a distinct possibility. I just returned from the parts store to get a set of plugs. One thing I have noticed is that it is not consistent. The worst was the one time I started from a stop and it felt like the tires were slipping on patchy ice. Sometimes it feels like an engine misfire, especially when I give it light throttle at cruise and I get a pop out of the intake (I think) and other times it feels like a trans slipping and grabbing. It happens from a stand still, light acceleration from low speed or light acceleration at high speed (that points me away from the TCC). WOT seems to smooth it out. Idle is smooth. Cruise set at any given speed is also smooth. Today while approaching my house at about 25 MPH I felt 2 distinct misses, almost like the ignition was momentarily cut off, then it was smooth again. All this and not one code to help me out. I guess if the plugs don't do it I'll have to start measuring the wire resistence. Anyone know what they should be? Next would be the coils and then the ignition module, though I am not yet sure how to check those. Oh well, back to reading the service manual.

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Making progress. I just went out in the garage and misted the wires (though I did not remove the conduit that the dealer put on) and coils. Nothing, engine was as smooth as a babies bottom. Then I did a brake torque with the hood up so I could watch the engine. Brought it up to about 2000 RPM and held it. It began to shudder a little bit (not real bad). I held it and let it continue for a few seconds. Then I noticed the SES light on. Sure enough there was the P0300 code. So I think I have it narrowed down to ignition, not tranny :) Needless to say I am feeling much better about this. Will takle the plugs tomorrow morning before work and eliminate that.

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once you change your spark plugs, check the plug wires for resistance. if all is well, check fuel filter, when was the last time you had that done. if the filter is old it can lead to low residual fuel pressure that can maybe make the idle a lil jumpy. as far as trans, i hope its not the trans. cause the "sliping" your talking about is definatly not the shift solinoids. good luck. report back.

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Making progress. I just went out in the garage and misted the wires (though I did not remove the conduit that the dealer put on) and coils. Nothing, engine was as smooth as a babies bottom. Then I did a brake torque with the hood up so I could watch the engine. Brought it up to about 2000 RPM and held it. It began to shudder a little bit (not real bad). I held it and let it continue for a few seconds. Then I noticed the SES light on. Sure enough there was the P0300 code. So I think I have it narrowed down to ignition, not tranny :) Needless to say I am feeling much better about this. Will takle the plugs tomorrow morning before work and eliminate that.

Mist the coils again, Larry. And brake torque the engine to push up the voltage required to fire the plugs while you mist the coils.

Had a similar intermittent situation on a 3800 Buick and one coil was breaking down.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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In terms of checking the resistence of the ignition wires, record the resistence of each on a piece of paper, if one is bad it will obviously stick out from the others and that will be your bad wire. Glad to hear its not tranny related, Mike

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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