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Engine runs rough. Want it to run smoothly.

Today I read out the spark plug wires. All the wires read perfect, but I have one resistor plug that reads about 500 ohms more than the others.

Would this higher resistance cause one plug to not fire as strongly?

I've got a fresh set of injectors installed, helped a little bit, but there's still a roughness that worries me.

I kind of wonder if my timing belt has slipped one tooth or so?

I removed the dist cap today and scrubbed the living crap out of the contacts, scrubbed the rotor, reinstalled, then had to lower idle by 300 RPM. That was weird.


Do you suppose the roughness could be coming from the dist, considering the idle change made just by cleaning the cap and rotor?

I can go through, one by one, and disconnect the injectors, feel a slight reduction in power, but the roughness is always there. I scrubbed my plugs the other day. They looked bad. Coated in shiny black goo, but still firing. I wonder if that goo was residue from injector cleaners I've run through the tank? I think I will pull and scrub them again.

I can't find anymore vac leaks, can find anymore grounds to scrub,.....

I'd say the engine, overall, is in great shape, but the roughness really bugs me. I can remember sitting in the driver seat of my buddy's Dad's 928 back in 1988, revving the motor, watching the tach needle climb, but not feeling anything through the seat or floor. I was shocked at how smoothly that engine ran. So I have a vague reference of how this engine should "feel", or how I want it to feel.

Rack and pinion is leaking, and has a torn boot....according to the safety inspector today. I was kind of impressed that was all he found, considering he used to maintain his old boss's 928 years ago.

This is Rachael Yamagata. I'm in love with her.

YouTube - Rachael Yamagata - Worn Me Down

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Old 05-10-2011, 07:36 PM
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Madman
 
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I see you did a "cylinder power balance test" with the injectors. Good job by the way going with injectors not plugs, (better for CAT). With a power balance test you are looking for a change in idle rpm/ the cylinder (disconnected) that drops the most RPMs is doing the most work...

"Shiny black goo" on the spark plugs is plug fouling and indicates one of a couple things. Either (1) your plugs are the wrong heat range for the engine, if they are meant for a hotter cylinder they wont be getting hot enough to burn the crap off and they will cause misfires; OR (2) you are burning oil.
The spark plugs are a more common problem because the guys at the parts counters usually don't ask enough information to help you get the correct plugs.
I also wouldn't go with super mega giga electrode platinum plugs as these are designed for quad-turbo Mitsubishi lancer evo's. Just get standard Bosch or NGK copper plugs. I dont know what year yours is but the spark plugs recommended for the 81-84 engine blocks "M28.09/10/15/16" are "Bosch W 8 D (W 145 T 30)"

If that doesn't work try a cylinder leakage test; you could be losing some compression somewhere.

I had a roughness problem and it turned out to be low compression in cyl #6 leaking out the spark plug because it wouldn't seat due to messed up threads, and also there was some coolant in the cylinder. So I'm rebuilding my engine now.

The distributor could potentially be a problem if the gap between the contacts and rotor is too large (excessive pitting), this would cause weak spark, but check the other stuff first. If you do test the spark strength and if it's weak check the coil resistances and compare them to specs.

I doubt your problem is timing belt slippage related because a jumped tooth would most likely make the engine not start or make it just non runnable altogether.

Hope this helps- that's all I can think of at 2:15 am.

-Anthony.
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Old 05-11-2011, 01:16 AM
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shiny black goo could also mean fuel fouled or plugs that have been run too rich according to this image.
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Old 05-11-2011, 03:40 AM
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I would suggest to put in the Bosch copper tip plugs and also get the Beru plug wire set that Roger sells its expensive but its a plug and play set then your ignition should be good to go, using the make the wires yourself kit leaves too many things in the air for a failed wire.
Every set i have installed worked as advertised
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Old 05-11-2011, 07:12 AM
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Yup, plain Jane copper plugs. Stay away from the quad platinum flux capacitor plugs too.
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Old 05-11-2011, 07:47 AM
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I never clean (scrub) plugs. Get all new ones they are cheap.
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Old 05-11-2011, 08:00 AM
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Quote:
Originally Posted by harborman View Post
I never clean (scrub) plugs. Get all new ones they are cheap.
We fought you a few times about Spark Plugs, but I'm glad you finally gave in and bought new ones.

86 32V no start
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Old 05-11-2011, 09:10 AM
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While extremely smooth, no engine is vibration free. What is the condition of your Motor and Transmission mounts? Collapsed Mounts can cause the oil pan to rest on the cross member, transmitting vibration to the frame, and you.
Old 05-11-2011, 09:50 AM
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Quote:
Originally Posted by MPDano View Post
Stay away from the quad platinum flux capacitor plugs too.
Why, I experienced much improved engine smoothness, responsiveness and start ability with the Bosch quad flux capacitors
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Old 05-11-2011, 10:11 AM
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Quote:
Originally Posted by riber.bentsen View Post
Why, I experienced much improved engine smoothness, responsiveness and start ability with the Bosch quad flux capacitors
Ahh, that's it. It's because I used NGK quad flux capacitor spark plugs
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Old 05-11-2011, 10:15 AM
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I'm running Bosch silver plugs, the ones recommended on the hood sticker.
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Old 05-11-2011, 01:46 PM
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Quote:
Originally Posted by dcrasta View Post
While extremely smooth, no engine is vibration free. What is the condition of your Motor and Transmission mounts? Collapsed Mounts can cause the oil pan to rest on the cross member, transmitting vibration to the frame, and you.

Mine has the solid motor mounts, and they look fine, plenty of clearance over the cross-member.
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Old 05-11-2011, 01:47 PM
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When I pull the injectors one by one, each has the exact same effect on the running condition. I was hoping to find one that made a substantial difference, but no.

Maybe it's just me.
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Old 05-11-2011, 01:48 PM
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After a cold start, I get some white smoke out of the tail pipe, but only for a few minutes. Probably have a weak spot in a head gasket, or some warping in a head that flattens out after warm-up.

When the engine warms up, it runs smoother, but I wonder if one cylinder is firing weaker than the rest. It just doesn't seem to have the harmony that it should.
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Old 05-11-2011, 01:51 PM
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Quote:
Originally Posted by Maleficio View Post
After a cold start, I get some white smoke out of the tail pipe, but only for a few minutes. Probably have a weak spot in a head gasket, or some warping in a head that flattens out after warm-up.

When the engine warms up, it runs smoother, but I wonder if one cylinder is firing weaker than the rest. It just doesn't seem to have the harmony that it should.
Have you done the compression check yet?? Cold...dry then wet...warm...
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Old 05-11-2011, 01:53 PM
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Quote:
Originally Posted by JhwShark View Post
Have you done the compression check yet?? Cold...dry then wet...warm...

Not yet. I don't have a compression gauge right now.
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Old 05-11-2011, 03:58 PM
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Correct ( JhwShark)
Save yourself some time and always start with the "Compression" Buy if you don't have a "screw in High quality Compression Gauge " , you well use it for many years
What you looking for is less then 10% difference ( 5% is better ) between Cylinders
Example : if you compression is say 180 / 185 / 182 / 186 /188 / 181/ 187 / 183.
(Expect yours may be higher Its a what > 1987 1986 ? )
now that's great > in fact any between 180 to 190 for example and the motor can be made to run smooth . If it does not run smooth then you must find out why BUT It's not any Major Problem..
Nice looking car By the way >
It sounds like you may have stumbled on to something when you worked with the distributor and then noted changes > I think you have checked the grounds but just check the ground on the Dist again > run a jumper from the Dist to ground.
**************** Great way to find Vacuum leak's fast *******************
Pull the Car outside somewhere so water on the ground is not as issue
With the motor running ( Idle ) Run low pressure water from garden hose ( talking a small stream ) slowly over all the places that have Vacuum .
" Yes you don't want to run it over the injector Hot leads or any other electrical connections. "
( but get the Injector seals for sure ! )
Just all the rubber hook up's and or Gasket area's > You can do the whole motor in a Min or so.
Now if you find a leak the motor well slow down right away as some water is sucked in to the motor > talking a small amount of water this well not hurt the motor >
I have used this Method for many years and it work's Great ! . finds the leak every time and fast.
A little water well not hurt a motor > think of the water Injectors for example.
**********************************
Put a pressure Gauge on the on the Radiator Reservoir to find out if you have a internal Leak.
Pump it to about say 15 / 18 Lbs and let it sit . It should Hold .
If she drops down try to re>torque the cylinder heads . Note any lose Head bolts. Don't over tighten the heads with the Aluminum Block.
Run the motor then re test after it cools
Look for leaks when the Pressure Gauge is pumped up. Check the side tanks or the radiator closely.
Cold Start Vapor / Steam ( if you want to call it Smoke ) is normal > Just condensation inside from sitting Cold burning off .

Last edited by aluminum; 05-11-2011 at 04:44 PM..
Old 05-11-2011, 04:27 PM
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OK since nobody has mentioned it and you are maybe running rich....How's your o2 sensor, bad crimps are pretty common. Some of the local motorheads here in the backwoods of Missouri solder/heat shrink them and then with a little chuckle, nick the insulation just in case the "reference air" story is not just bad joke.... Bruce
PS... You think maybe you could get your QA guy to sign off on a repair like this?
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Old 05-11-2011, 05:29 PM
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Good point. Is O2 sensor new? How is it wired? How does car run in open-loop map mode without O2 sensor hooked-up.


Besides that, you have the
full set of manuals. Use them.
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Last edited by Landseer; 05-11-2011 at 05:35 PM..
Old 05-11-2011, 05:31 PM
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Thanks for the tips, Aluminum.

Sounds like some good tricks. I replaced all the vacuum hoses last summer with some nice silicon type. The last leak I found was the flexible coupler between the hard lines going to the auto tranny. After that, I can't find anymore leaks.

I've gone through all the grounds I can find. I replaced a few, scrubbed the others, and added extras, including one from the dist. That one actually made a difference in running quality.

This afternoon the car ran very nicely. It's not consistent, though. Tomorrow it may run rough again.

It's got a nice, new radiator from the PO. The hoses are in great shape. New thermostat.

It's nice to open the hood while it's running and not smell gas vapor anymore. I replaced all the soft lines when I changed the injectors the other day. Replaced the fuel damper and passenger fuel regulator, too. They were both leaking fuel through the vacuum port. The driver side one has always been dry. I presume it's working okay. The car no longer has that strange rumble at idle. I figure the raw fuel being sucked into the intake from the regulator and damper were causing the rumbling. All gone now.

Now I just want to get the engine singing instead of sounding like Cookie Monster.

But it may just be me.
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Old 05-11-2011, 05:34 PM
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Old 05-11-2011, 05:34 PM
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