Rough running 3.8L

Topic: Rough running 3.8L (Read 1323 times) previous topic - next topic

Rough running 3.8L

October 10, 2007, 02:52:13 AM

Well where to start I am new to the fourm and have a much loved 85 cougar. It has a 3.8L V6 with 145000 miles recently it started running rough and vi-berating heavily at idle through high rpm's with no apperent loss of power. So I did plugs,cap,rotor,wires. this had minial change on the trouble so I swaped out the dizy with a spare because I found oil in the area of the electronic's & still no change. So I thought vacume leak I checked all the hoses & fittings even clamped off the vacume hose to the trans & still no change. I did an Engine systems scan (Autoxray EZ-scan 5000) on the car, It passed no trouble codes for engine off & engine running. The TBI/ Injectors seam to be delivering fuel as I have no power loss. could this be EGR related or am I missing the picture here.

Rough running 3.8L

Reply #1 – October 10, 2007, 07:07:15 AM

does it vibrate when you park it and go through the revs? or is this vibration at speeds? it doesnt sound like its vibrating from a miss if it has full power. if it vibrates only at speeds, check wheels balance first, might also be a driveshaft also. but it sounds like it might be a harmonic balancer if i understood you right, and it does it all the time, driving or not.

Rough running 3.8L

Reply #2 – October 10, 2007, 08:03:51 AM

I used to have a 3.8.I had the shaking as well,and it turned out to be a bad motor mount.

Rough running 3.8L

Reply #3 – October 10, 2007, 09:19:53 AM

usually the CFI systems will require CFI base plate gaskets every so often. I know this motor / wiring / vac lines front to back but it seems like you covered everything.

Sounds like you shot gunned the problem and lots of good oem parts were tossed.

Spray carb cleaner along the CFI base and along the back of the cfi as well while the car is running. If there is a change in rpm, pinpoint the problem area. The same can be done for your vac bank that resides behind the coolant fill tank.

If you still have the smog system on there, you can cap off the black and tan at the solenoid bank to iliminate those for cracked lines while troubleshooting. Basicaly, all you need by way of vac is the green and red hooked up. green being for the egr and red being for the main vac feed.

There si so much to go over, but check out my diy link below for more info on your engine setup. Ill bet its the cfi gasket though. There is a gold fitting on the rear that carbons up and you can see the carbon unless you remove the cfi. That gold fitting ties in the egr system so yes, this could be egr related. If you put suction on the egr vac fitting and....if it holds,,,, the egr diaphram is good. To test the evp sensor, use my diy link as well.

Check vac ........and let us know.

Rough running 3.8L

Reply #4 – October 10, 2007, 09:29:48 AM

On a side note, ill share with you what i do for the 3.8 to assist in hearing the vac leak.

Drill a hole in the driver side of the fan shroud about 1/2''.
drop a long bolt in the hole
rotate fan until it hits the bolt.
start car
fan will just sit there and bind against the bolt.

Why do this?,,, so you can get rid of that fan noise while hunting the vac leak by ear only. Of course dont do this for more than the time it takes to heat up overly. If your temp guage works, you can peek at it once and again. This is best done with a bone cold motor so you have max time to hunt.
just pull the bolt when your ready to let the fan run.

Rough running 3.8L

Reply #5 – October 10, 2007, 09:47:17 AM

Also remember that those plastic vacuum lines are very brittle by now. Be carefull removing vacuum lines they will shatter. The EGR is both electronically and vacuum operated. If the diaphram is broken you'll have a big vacuum leak but not at idle as there's no vacuum signal below 2500 or so rpm, at least there shouldn't be.

Also jcassity is correct about carbon under the CFI. It's not hard to remove but be aware that there's about 65 psi of fuel pressure to the fuel line at the CFI. Unless the car has sat quite a while since running it could be a hazard. Pull the fuel pump fuze and crank the engine. It may run a bit but when it stops the fuel pressure will be zero.

Rough running 3.8L

Reply #6 – October 10, 2007, 02:56:19 PM

Quote from: tbirdsps;181778

Also jcassity is correct about carbon under the CFI. It's not hard to remove but be aware that there's about 65 psi of fuel pressure to the fuel line at the CFI. Unless the car has sat quite a while since running it could be a hazard. Pull the fuel pump fuze and crank the engine. It may run a bit but when it stops the fuel pressure will be zero.

why bother when you can just stick an ink pen in the shrader valve where you test presure and relieve said presure:hick:

Rough running 3.8L

Reply #7 – October 10, 2007, 03:26:16 PM

Oh yea, forgot about that! I was concerned about fuel squirting all over which still could happen out of the schraeder:flame:

What a BONE HEAD

Reply #8 – October 12, 2007, 02:57:57 PM

Thanks for helping me to retrace my previous steps while trying to get a look at the passenger motor mount I saw what i had missed:toilet:

Total Brain FART!!!!!!!!!!! when I previously looked at the harmonic balancer I didnt see that it was comming apart And when I stabed the new dizy I just did a quick time my ear to check things out, Yes I do own a Timing light and it would have been prudent to have timed (or at least tryed to) it when I stabed the dizy. So I am shure that a new balancer will fix the trouble.:hick:

:D Hey at this point it should run like a top I mean a complete tune up fresh water pump new valve cover gaskets cleaned out EGR & baseplate cleaned under CVT, PVC, new Thermostat

Rough running 3.8L

Reply #9 – October 12, 2007, 03:20:06 PM

I never would have thought about harmonic balancers and motor mounts. I'll have to remember that.

What next

Reply #10 – October 13, 2007, 01:13:28 AM

Well the New Harmonic balancer did the trick, she now purs like a cat should. But she seams to lack a little power at take off but accels well after the inital bit of bogg. I set the timing at 12-14 btdc I think I should back it off to the factory spec's of 10 btdc. THE real question is how much damage was done to the front main bearing having been forced to drive about 200 miles at freeway speeds:flame: & how to tell without pulling the pan & cap, wich I cant bear the though of it right now.