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23K views 102 replies 24 participants last post by  jones105n 
#1 ·
Well I guess it's my turn. '97 Deville. 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 occasional 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 normally 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. Maybe this WOT stuff is not such a good idea after all. NO codes, temp normal 212f, no warning lights. What do you guys think?
 
#2 ·
I too had the same problem with my SLS running fine at times but missing/stuttering at driving speeds. It would give a little slip right when you take off, made me wonder if the tranny was slipping for a second. It got more noticeable as the car became warmer. Pulled all the plugs, they looked great. The problem was that the wire caps were not down all the way on the plugs on 2 of the back cylinders. I guess as it warmed up, the expansion caused the bad connection. Reseating them got rid of the problem. My plugs and wires were only 30K old, so I didn't think they were the problem, but sure glad I checked. Good luck!

Jim from WY
 
#3 ·
I have this same problem with my '94 N* and described it on this forum several weeks ago. Was counselled to check the EGR ports in the spacer plate between the head and intake manifold - I guess these can clog and cause poor part-throttle cruising performance. I thought it at first kind of felt like the TC was switching in and out of lock or something trans-related, but advice from some excellent forum members directed me toward the EGR ports first. Don't know if this applies to your year vehicle. I haven't done the work on my car yet, but will this winter. Please post your experience. Sincerely, Andy.
 
#4 ·
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. I'll report my findings when I get to work. 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. ???
 
#5 ·
Well, there was no change. It really has me confused. When I start from a stop it feels like the tires are slipping as if on patchy ice (slip, grab, slip, grab) which make me think trans. When I am at cruise and I lightly press the throttle it will studder or chuggle and and I can hear and feel an occasional pop or bang that sounds almost like a backfire which makes me think ignition. When I get on it hard it seems to run smoother. Maybe I'll change all the plugs to eliminate that and see what happens. This really has me baffled.
 
#8 ·
Plugs and wires have 92K on them. They did not look too bad other than what was described. Coil are another possibility I'll have to check out along with the wires. They were untouched til the fuel rail replacement a couple of weeks ago. .

I just got home from work and noticed another symptom. I normally 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.
 
#9 ·
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. I picked up a new set of Delco 41-950's this morning so I will tackle the plugs tomorrow morning before work and eliminate that.
 
#10 ·
Brake torquing this powertrain, especially when it's hot, is not conducive to long transmission life. Stop doing that! :D

The thump in your floorboards is from the engine/transmission mounts. I totally agree your problem is almost certainly ignition. Hopefully the plugs will be all it takes.

I wonder what the dealers are doing that screws up our ignition systems on these fuel rail recalls. Yours is the fourth car I've heard develop this problem soon after the recall. I wonder if some of the plug wires get really bent enough to cause stress fractures in their conductors.
 
#13 ·
I needed to replace the wires on my N* at 70,000 miles. I could feel a miss or stutter and an occasional pop or low level backfire. The 0300 code was never set. The best I could figure was the spark was jumping from one wire to the other in a place where they touched each other or ran in parallel then traveled on to fire the wrong plug causing a slight pop or backfire. When I changed the wires it all went away. I did change the old plugs at the same time even though they still looked good.

As to a problem of missing or skipping caused by the ignition wires after the new S/S rail install, think about it. The wires are not replaced under the recall and if they are old you may have a problem of the spark jumping from the wires to the nice new S/S fuel rail and on to ground. The plug wires lay down on the rail in many places. That means many places to ground the old wires. Remember the old fuel rail was plastic and the intake is plastic about the only metal the wires used to touch was the valve covers and now they touch the metal fuel rail. I didn’t have any plug wire arcing problems with the new fuel rail because my wires are new.
 
#14 ·
Well I changed the plugs this morning and I am glad to say she now purrs like a kitten and runs like a Thoroughbred. I have never seen a bad plug or plugs give such conflicting symptoms. As I said, I always think the worst. Gotta stop doing that. I think it is partially due to spending too much time here . Out of 8 plugs only one had a slight remnant of a platinum tip. In fact, most were slightly eroded where the platinum tip had once been. All gaps were in the .060 range. I can now feel the torque converter lock up again at 41 MPH and RPM at 70 MPH is steady at 1950 RPM.
Thanks to all for the help, suggestions and moral support. Oh yeah, and apologies to the dealer for what I was thinking.

Haymaker,
When the dealer replaced my fuel rail, they also installed plastic conduit on the plug wires to prevent shorting out on the new rails. I think that is part of the recall as I have heard others mention that as well.
 
#17 ·
Had exact same symptons on my 92 eldo awhile back. Terrible bucking and stalling at varying engine loads. The problem was loose Positive battery cable connection to starter. My guy tightened up the nut on the starter with a long socket extension and that was it. and he did it for free!!! Most honest mechanics in all of Queens/Nassau, NY Union Tpke and Lakeville road, Lake Success. Love those guys..
 
#18 ·
Well, it appears I spoke too soon. On the way to work this afternoon I got the same stutter, chuggle, misfire in the exact same location on the exact same ramp as were it first started. I is intermittent however and I was unable to duplicate it later. I suspect there are demons involved here. About the only explanation I can come up with (other than demons) is that when I changed the plugs, I jostled the wires and temporarily fixed the misfire.
 
#19 · (Edited)
I checked the resistance on my plug wires. First let me say (again) that electrical is not my strong point, so if I say something stupid, be gentle. Here are the readings I got with the DVM set at the 20K setting.
#1 2.01K
#2 2.87K
#3 1.46K
#4 3.00K
#5 1.07K
#6 2.99K
#7 1.39K
#8 2.67K
Do these readings look ok? If so, the next step has to be a coil. The mis seems to me intermittent and more so when up to operating tempurature. Can a coil be intermittent? Also, the '97 service manual says on page 6-428 step 9, after locating a misfiring plug, check the resistence on that cylinders wire and it should not be above 15K. If I move the decemal over one place, most of mine are above 15K! Does that mean most of my wires are bad?

Also, are GM coils all the same? If the wires appear to be good, can I swap a coil from my wifes '96 Bonneville 3800 series II to eliminate a bad coil?
 
#20 ·
Well, I just swapped the coils one by one with a coils I took from my wife's car. Same symptoms, so the coils are good. The only question now is what those readings from the wires mean. If I used the wrong setting and move the decimal over one place that would tell me all but 2 are too high. Can someone confirm that?
 
#21 ·
One of the easiest ways to check you plug wires is in the dark. It would be a good idea to have a working flashlight on hand before you start the test. You will need a very dark location for this test to work. Remove the beauty cover, warm-up the engine, remove the under hood light bulb and turn off the headlights. Ask a helper to get in the car roll down the window and close the door (the interior light must be off). You will need to allow your eyes several minutes to adapt to the darkness otherwise this test will not work. Stand by the drivers side fender with the hood open, ask your helper sitting behind the wheel to start the engine and try to duplicate the conditions that cause the engine to miss, skip or stutter (never throttle up against the torque converter). You must keep your hands, head and clothes clear of the engine. If you plan to ask the helper to place the car in gear, never place a foot in front of the tire or you body in front of the car. Change the viewing angle to insure you have seen every wire over its entire length including the coils. You may need to go around to the passenger side to gain another viewing angle, but never stand in front of the car. The test should include engine at start-up in park at idle, off idle, 1,000 rpm, 1,500, 2,000, 2,500 rpm. Then block the rear tires and ask your helper to hold the brake firmly and place the shifter in drive then test at idle, off idle but never against the torque converter. I realize the helper can’t see the tachometer to change to different rpm levels but it’s ok to guess. Just remember there is no need to race the engine at a high rpm for this test to work. Just ask the helper to hold each one of these rpm levels for five seconds or so. It will be quite evident if any of the wires are leaking.

I have found this to be a cheap yet effective test and best of all, no special tools required.
 
#22 ·
Idle seems to run smooth. The dealer installed plastic conduit on all the wires so I doubt they are "leaking" unless it is behind the right bank where there are none. I seem to get this mis (at least this is when it's noticeable) at about 40 MPH or better under light loads. That is when the TCC engages so there is more load on the engine. WOT or harder acceleration seems to run ok or at least is not noticeable. The only way I could duplicate it one time in the garage was brake torquing it to about 2000 RPM and holding it there. I don't want to do that again but at least that tripped the SES light and set a P0300 code so I new it was ignition related. I suspect plug wires but don't want to throw parts at it til I am sure those readings confirm it.
 
#24 ·
I'd have to agree... pull off the conduit, and do the Bbob test - mist them with water in a dark place (careful not to fall or touch anything). I bet you'll see all kinds of arcing. Plug wire resistance just tells you that it's not completely broken inside. Doesn't tell you if it's shorting out externally to something (which is a problem with 50,000+ volts)
 
#26 ·
Ranger, sorry it took a while to respond, I've been jammed up at work. It sounds like you need a set of plug wires. Factory wires have that conduit around them already, so if you didn't have any on yours, it's very likely someone changed them before. Sounds like the tech was doing you a favor at the dealer, since that isn't part of the recall. One way to tell for sure is look for corresponding cylinder numbers on the wires themselves. If they are not numbered, they have been replaced. Also make sure there is no carbon tracking on the new plugs you have installed, as evidenced by black lines that resemble cracks on the porcelain insulators. Also, be sure to stick with ACDelco wires, as I have seen pretty crappy aftermarket ones. I know they cost an arm and a leg, but you will only have to replace them once. Good luck, and let me know how that turns out.
 
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