'87 3.8 running poorly (mostly under load) June 20, 2008, 10:19:22 PM So I'm driving down interstate from the Magic Cityto the Rocket City a while back and I notice the car beginning to vibrate. Hmm. Eventually I have to slow to 67 or below otherwise it shakes enough to make objets in the rear view mirror get fuzzy. It idled pretty good, but would begin to shake (which I think is a manifestation of a lot of missing) on acceleration. It does it whether all the time, with no regard to closed/open loop.Things I've done so far:Removed the plugs.[INDENT]Driver's side were all richPassenger's side were all lean[/INDENT]Checked vacuum at idle - seemed a bit low[INDENT]19.5" in park16.5" in drive[/INDENT]Checked fuel pressure. The gauge wasn't long enough to watch it while the hood was down, so I just backed up in the driveway and floored it for about 10' (real smart, eh?)[INDENT]Solid 38psi[/INDENT]Ran the codes. Ran KOER in a row twice to see if the 42/92 (rich both sides) would clear up. They did, but a 44 (thermactor inoperative passenger's side) popped up. [INDENT]KOEO - 11/11KOER #1 41/92KOER #2 44[/INDENT]I still need to check timing - mainly to verify the damper hasn't slipped. But since it only vibrates/misses under power I don't think that is the problem.I'll also recheck the plugs to see if the new ones are repeating the old pattern. Also take a look at the distributor cap look for any patterns/wear. New/nearly new (<15k) parts[INDENT]Ignition CoilSpark PlugsSpark Plug WiresDist. Rotor/Cap[/INDENT]For full disclosure, what I thought was an exhaust leak was a loose spark plug (#2 - passenger's side) that shot out in early May. Once I replaced it the leak was gone and it ran like a top again.So, any advice at what I should look for? This is very annoying, especially since I finally finished the 5lug swap and have the 99+ axles in. I want to drive! Quote Selected
'87 3.8 running poorly (mostly under load) Reply #1 – June 21, 2008, 07:42:34 AM Humm, you've covered it fairly well...I know you said the plug wires are fairly new, but I'd check the resistance of each one... Also check the boots and inspect the spark plugs... A interminant miss on the '93 Merc was caused a bad boot, which left a almost invisible track down the side of the plug... Any chance you could have gotten a bad tank of gas??? Quote Selected
'87 3.8 running poorly (mostly under load) Reply #2 – June 21, 2008, 11:53:20 AM Dumb question (:hick: ) but are you sure it's a engine miss? I had a problem awhile ago with vibration crusing above 70 mph and upon acceleration above 60 mph. Turned out my rear u-joint was bad and replacing it (and the front one just for good measure) solved the problem. Quote Selected
Problem Fixed! Reply #3 – June 21, 2008, 09:54:20 PM Quote from: thunderjet302;224218Dumb question Actually, not a dumb question!I took the car for a test drive this morning to quantify the problem. The vibration was worst from (1)20-30 mph, but it was the same no matter if it was in 1st, 2nd, or 3rd (2)65+mph, did it in both 3rd and OD.So, between your suggestion and that data, I took a look at the u-joints. There didn't appear to be any play in them (that I could tell), but I took the drive shaft off anyway. The joint by the axle was fine, but the joint by the tranny only moved on one if its axes. The picture at the bottom of the post is from that joint. The rear joint, even though it moved freely had significant wear on the bearing surfaces when I took it apart. I'd guess they're the originals (236k miles).The vibration was so close to how it felt when #2 plug fell out that I was certain it was an engine problem. Quote Selected
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