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Old 03-26-2008, 08:20 AM   #1
92SC2
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Default Chugging/stumbling at constant highway speed

95 SL2 152,000 miles.

As you may recall I just swapped a used (junkyard) engine into my 95 SL2, the engine also came from a 95 SL2. I replaced the plugs with NGK V-powers as no copper plugs were available. Both ECTS sensors were replaced with new brass units. There was also a brass unit in both the donor engine and the original FWIW. There was also a new ECTS plug installed into the wiring harness of the original engine so I suspect that there was corrosion on it from the original engine. I cleaned the EGR pintle with carb cleaner as best I could and just replaced the plug wires last night and I still am getting some hesitation and stumbling. I originally thought that the guts from the catalytic converter were clogging the works as it was loose and sliding around so I gutted it a couple weeks ago. No dice, it's still screwing up and chugging. The plugs only have ~1,900 miles on them and they're black around the base but with a tanish color developing on the electrode. I'm not too concerned with that just yet, but I'm going to keep an eye on it. So I'm down to changing the coils as my last logical step. I have the two from the original motor sitting on the dryer in the garage. Any other suggestions?

EDIT: I also installed a new fuel filter and the plugs were all gapped a .040" per spec. The stumble seems to occur mainly between around 55mph giver or take 5mph. It does occur up to 70mph though. I guess it could possibly, maybe be a bad TPS but that seems kinda weird for a TPS to act like that.

Last edited by 92SC2; 03-26-2008 at 08:30 AM.
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Old 03-26-2008, 08:54 AM   #2
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Default Re: Chugging/stumbling at constant highway speed

I vote for replace the plugs Ė donít care how many miles are on them! Read my other thread about the difference between AC Delco plugs. A lot of good input their.
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Old 03-26-2008, 09:45 AM   #3
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Default Re: Chugging/stumbling at constant highway speed

Cleaning the EGR valve may not correct it if its the valve that's making the engine stumble. What you can do is disconnect the electrical plug to the EGR valve (it won't harm the engine but the SES light will turn on) and as long as the engine has a good idle speed, drive normally. If the stumbling goes away its the EGR valve, a simple black and white test. Nothing else is tampered with so you're doing a specific test by simply leaving the EGR valve in its closed position where exhaust isn't fed into the intake manifold in the usual manner. The steady idle is the only indication that the EGR valve is in its closed position.
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Old 03-26-2008, 10:36 AM   #4
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Default Re: Chugging/stumbling at constant highway speed

I'll check that, but the car has a decent idle right now. Maybe this will improve it. Either way it ought to let me know if it's the EGR. Thanks.
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Old 03-26-2008, 03:32 PM   #5
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Default Re: Chugging/stumbling at constant highway speed

Hey 92SC2 check the MAP sensor port and intake port for gunk.
Had same chugging, I unplugged my EGR ran good replaced it (OEM $140) and no change. Replaced ALL of the sensors and the problem happened when I tried to clean the intake prior to assembling the rebuilt motor, I left the MAP in place and dumped a 'ho bunch a black gunk into the MAP sensor. Never thought to take it off to flush the carbon out.
First sentence in the Haynes maual about the MAP is that it controls the ignition timing and fuel injection when warmed up-that is when I had the problem it idled fine and ran good when cold (ECM in closed loop?). 14-18 MPG now it's up to 24!
Hope you find your problem.
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Old 03-26-2008, 07:23 PM   #6
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Default Re: Chugging/stumbling at constant highway speed

Hipster, how did you clean all the black gunk out of your intake? Did you disassemble it all and clean it or was there another way?
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Old 03-27-2008, 09:14 AM   #7
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Default Re: Chugging/stumbling at constant highway speed

Just an update, I had to drive about 30 miles away yesterday afternoon to get to a last minute meeting and my boss told me to get out there like RFN. So I pull onto the interstate, down shift into 3rd and gun it. Unhealthy things happened. In short the flippin exhaust came apart on me. I had to cut the 1.75" line that is just in front of the muffler in half and when I used a 6" sleeve and two clamps to hold it. Well I guess the rocking of the engine while shifting finally pulled it apart. I had no tools and I can't fit under the car so I ended up driving the car all the way out to the meeting sounding like I was bringing hell itself with me. Then I drove it home and parked it. Now it looks like I'll need to replace the resonator too. So I'll take your advice am see if I got some gunk in the MAP sensor while spraying carb cleaner into the intake and I'll check the EGR too. But not until I patch up the rest of it.
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Old 03-28-2008, 12:29 PM   #8
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Default Re: Chugging/stumbling at constant highway speed

Quote:
Originally Posted by kethomps View Post
Hipster, how did you clean all the black gunk out of your intake? Did you disassemble it all and clean it or was there another way?
I had it off the block and tried to clean it-then on the web I found why it gets nasty. PCV valve sucks in crankcase vapors and coats it all over again. So I gave up on cleaning. Just pull throttle body off, clean it and surrounding intake area and call it a day.
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Old 03-28-2008, 12:31 PM   #9
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Default Re: Chugging/stumbling at constant highway speed

92SC2-good luck on the exhaust repair.
Keep us posted on the MAP sensor!
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Old 03-29-2008, 08:53 PM   #10
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Default Re: Chugging/stumbling at constant highway speed

Quote:
Originally Posted by Hipster View Post
92SC2-good luck on the exhaust repair.
Keep us posted on the MAP sensor!
Will do. Hopefully I'll remember to do it tomorrow.
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Old 04-09-2008, 05:22 AM   #11
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Default Re: Chugging/stumbling at constant highway speed

Alright, here goes.


I fixed the exhaust, it's all back together. I pulled the MAP sensor, there was a little crud in there that I cleaned out with carb cleaner. I also did a piston soak while I was at it. The misfire is still present and IMO getting worse.


This morning on the way into work 3rd gear @ 40mph/3500 rpms...it was stumbling all over itself. Lasted until a little after 4000 rpms and smoothed out some. 4th gear was similar. 5th gear at 2800 rpms the chug was present, but not as violent/strong. It feels like an ignition induced misfire but I'm not sure if it is the coil or maybe the ignition module? Could be something else.


Plugs are still the NGK V-Powers a little over 2k miles on them, wires are new, ECTS's are both new and brass.

Is there and easy way to diagnose the coils without swapping them out? Anything else it could be? TIA
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Old 04-09-2008, 06:02 AM   #12
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Default Re: Chugging/stumbling at constant highway speed

I have to ask, did you clean the port on the intake and the small port on the MAP sensor?
I tested the MAP sensor with a safety pin, volt meter peice of tubing to suck on to create the vacuum needed to change the voltage reading.
The coil packs have a resistance rating that you can check with an ohm meter.
Are the sparkplugs showing any uneven traits?
If so, switch coils left to right and see if it follows the switch.
That's all I can think of.
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Old 04-09-2008, 06:33 AM   #13
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Default Re: Chugging/stumbling at constant highway speed

Quote:
Originally Posted by Hipster View Post
I have to ask, did you clean the port on the intake and the small port on the MAP sensor?
I tested the MAP sensor with a safety pin, volt meter peice of tubing to suck on to create the vacuum needed to change the voltage reading.
The coil packs have a resistance rating that you can check with an ohm meter.
Are the sparkplugs showing any uneven traits?
If so, switch coils left to right and see if it follows the switch.
That's all I can think of.
I sprayed carb cleaner down into that hole and even stuck the strawinto hole and sprayed some more. I forgot to take pics of the plugs but they all looked pretty much the same from memory. I knocked the black off of one when Ifirst pulled them for whatever reason. The others were developing a light tanish color on the electrodes and black everywhere else. There was a little bit of oil around the base of the #1 boot but nothing drastic. The new gasket is firmly seated and the cover is torqued to spec. I gave it a little extra tweak this last time around. The boots and even coils have dielectric grease on them. I need to get an ohm meter.

For the record I cleaned the connectors on the coil pack towers and cleaned/used dielectric grease between the coil packs and the mating surface on the block. Hopefully that's not causing an issue.
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Old 04-09-2008, 07:14 AM   #14
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Default Re: Chugging/stumbling at constant highway speed

Dang, you got me.
Tried unplugging the EGR?
Will send SES light of course.
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Old 04-09-2008, 08:29 AM   #15
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Default Re: Chugging/stumbling at constant highway speed

Quote:
Originally Posted by Hipster View Post
Dang, you got me.
Tried unplugging the EGR?
Will send SES light of course.
Haven't done that. I may just try swapping the coils out with the coils from the original motor and hopefully source some copper NGK's in the area. The EGR pintle was cleaned before I initially fired up the engine. I could try to re-clean it and maybe take it off and fire the car up like that for a few seconds.


On the exhaust, I ended up with an 18" 1.75 pipe, flared on one end, and a 1.75"-1.75" ID coupling and cutting some of the mangled remains from the exhaust. Putting everything in place and using pop rivets and regular clamps to secure everything. the idea being that the rivets should give an extra line of protection in case a clamp fails again.
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Old 04-10-2008, 11:54 AM   #16
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Default Re: Chugging/stumbling at constant highway speed

Hope the coil swap helps out.
What part of the exhaust did you have to repair?
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Old 04-10-2008, 01:32 PM   #17
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Default Re: Chugging/stumbling at constant highway speed

Quote:
Originally Posted by Hipster View Post
Hope the coil swap helps out.
What part of the exhaust did you have to repair?
Coil swap is on the list for this weekend. Too much stuff to do in the meantime. Long version of the story about the exhaust...the chugging I am experiencing was originally thought to be from a clogged cat sine the original engine was smoking, knocking, and in general disrepair and the cat rattled around. I could not get the 3 nuts loose at the flange behind the cat so I cut the pipe behind the resonator, cut the nuts loose, gutted the cat, replaced the studs in the flange with bolts, and used a coupler to repair the initial cut through the exhaust pipe. Well that coupling came undone and I ended up dragging the exhaust for 30+ miles to a meeting and then home. Everything is back in place now, clamped and riveted. Hopefully it stays.


I will keep you posted on the coil swap, might even change plugs again too for poops and grins.
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Old 04-10-2008, 02:58 PM   #18
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Default Re: Chugging/stumbling at constant highway speed

Please do, and good luck!
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Old 04-14-2008, 09:04 AM   #19
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Default Re: Chugging/stumbling at constant highway speed

UPDATE:


Alrighty, Ifinally got around to replacing the coils on my 95 SL2. I used the coils that came off of the original engine, used a wire wheel chucked up in a drill to clean the posts, and rear contact area, and put it in.

While waiting for it to warm up after replacement, I put my hand on the front cam cover (exhaust) I could feel a slight shudder with my hand over the #2 cylinder, but not really the rest. It was rather slight. Now, on the road it SEEMED to be doing better, however at a constant speed it still stutters. It's almost like the clutch disengages for a second or like it was in the middle of a shift if it was an automatic....driving along ......_...._......_..._ where the "..." is normal pluggin away driving and the underscore is the intermittent pause. It happened @ 35mph, 55-60mph, and even slightly @ 70 mph.


Would or could a bad TPS cause that? Should I swap out my MAP sensor from the old engine?
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Old 04-14-2008, 10:44 AM   #20
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Default Re: Chugging/stumbling at constant highway speed

I'm wondering about a vacuum leak. Have you tried spraying some carb or brake cleaner around the instake manifold to see if it causes the idle to change?
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