oatburner99

Alright guys, kinda stumped here...

My 90 coupe has developed an engine vibration.

Specs are:

150,000 mile stock block (bottom end) Gt40 heads, upgraded springs (alex spring kit) , e303 cam, gt40 lower and explorer upper. 65mm explorer t/b stock egr, bbk cold air fender intake kit, bbk longtube header's with offroad h pipe. stock dizzy, coil, electric fan, 3g alternator, factory MAF and 19 lb injector's. Fuel pressure is 39 psi with vacuum off, 41 with vacuum on, initial timing is @ 12 degree's.
UPDATED:
First things first, I ran KOEO and had no codes. Then with KOER I originally got a code 91, which was a lean bank driver's side (02), so doing some semi easy troubleshooting (actually not reading like I should have) I swapped the driver's side 02 sensor over to the passenger side, and the passenger side over to the driver's side. I disconnected the battery (Although not long enough I think) and again ran KOER and got a code 91 AND 41. The 91 I'm assuming was still in KAM, and is why I had both l/h and r/h o2's lean. Why is it lean? O2 sensor's read nothing but oxygen so what is causing the car to be lean? I think that I had a defective spark plug wire on #1 cylinder, so I upgraded to FRPP wires and that made the code 91 go away. Now I get a code 94, 44 which is the thermactor injection not working. Which are just soft codes. I pulled all the plugs (motorcraft coppers) checked the gaps (0.050) they all looked good, however I opted to replace them anyway. The car still shakes like crazy (parked in the garage, not driving) When I did KOEO and KOER the car was at operating temperature. I've flushed the coolant system, replaced the ECT as well. Conducted a cylinder balance test, and it passed with a 90. I've looked at the harmonic balancer and it's not pretty, it's dry rotted, but it's the only thing I can think of that is going to give me a vibration. The vibration could be the harmonic balancer or maybe a miss? I've routed #5 and #6 spark plug wires away from each other (being they are close in the firing order) and checked the other's as well.

I did the H/C/I swap around 6 months ago, engine has new motor mounts (stock) as well as a new transmission mount, clutch is a SVE mongoose from LRS, that i replaced just about a year ago. Reconditioned the flywheel. What's weird is when I try and start the car when it's cold (been sitting overnight) it'll start but I have to stay in the throttle to keep it running, and it shakes bad. Once it's warmed up, it'll stay running and idle around 900 rpm with no problem however it still shakes at certain RPMS (raising the rpm's in neutral in the garage) I'm thinking i have 2 problems, one mechanical (harmonic balancer) and a fuel/ignition/electrical problem...I know salt and pepper shakers are notorious for having problems, I'll be honest I've probed so many wires I can't remember, however I know that TPS does NOT have it's 5.00 reference voltage that it should have. Does anyone have a wire diagram for the sensor's on the motor, for the engine harness as well as the harness (PCM all the way to the engine bay? I need to see what other wires that are tied in with the TPS, ECT,BAP that share the 5.00 reference voltage. Thanks guys!

mjr46

you have misfire, pull plug wires one by one until you get to a cylinder that produces no noticable rpm change = misfiring cyl........wear protective gloves when conducting test and or insulated pliers

oatburner99

Okie Dokie....I'll try that after work....just worried about continuing to run the motor trying to diagnose the problem.

mjr46

if it's a misfire as I state, it won't hurt it as long as you don't drive it on the highway or run it for long periods like such, idle testing won't hurt it, besides a solid misfire as such won't take long to isolate, when you find the dead cylinder,swap a said cylinder plug wire to diff cylinder, if misfire stays on same cyl, do such with the plug, if it still stays on same cyl, then compression test, if compression is good on said cyl then inspect rocker arms and make sure none broke and or came loose and or a bent push rod...

oatburner99

In your experience, have you ever heard of a bad harmonic balancer CAUSING a misfire...the car is maintaining initial timing (spout out) @ 12 degree's. Car shakes but I'm really now (after reading what you said) thinking it's a plug issue. I couldn't find anything wrong with them, no cracks, nothing was broken off....It's not the firing order, I've triple checked that, and placement of the plugs on the cap. Cap and rotor were good too.

mjr46

balancers I've had probs with have wobbled, so it was more of a vibration throughout the whole car, with a misfire, it'll have a noticable lack of power and rough idle and feel it out the tailpipe often as a putting sound.

oatburner99

OK update: the shaking doesn't get worse with increase in RPM it only happens at certain RPMS. Shakes at 1300-1400 rpm but smooths out at 1500 like glass. So I pulled all the plugs, and replaced them with new motorcraft copper cores gapped at .050'. Hooked everything back up and took the car for a short drive, I found that anytime I went over 3100 rpm the check engine light would come on, as soon as I got out of it, the light would go out. Took it back home, ran the codes. Got a 94,44. (thermactor injection system inop) Same codes I had before...

What's the next step for me to take? I'd assume pull plugs one by one, as you stated. Question: Would an exhaust leak on a header flange contribute to my issue? It leaks right on the fwd edge of the #5 cylinder above the forward bolt.

mjr46

make sure the balancer hasn't spun, find true tdc, pull no1 plug and put finger over hole until air starts to escape and shine light in hole and see when piston is at or around tdc, this will get you close, if the balancer has spun quite a bit then the 0 on the balancer won't even be close to the pointer, but as I stated before if it has a heavy misfire/shake at idle do the pull plug trick to isolate cylinder not contributing or do a koer power balance test and see if it picks up a misfire/ bad cyl. Exhaust leaks before o2 can affect a/f if they are bad enough and skew o/2 readings thus affecting fuel calculations.

oatburner99

I did mark the balancer with a slippage mark about 2 months ago, and it hasn't moved. I did do the power balance check after the KOER and it passed. However during the test the computer raises the RPM to 1500 rpm for about 15 seconds, then drops down to 1300-1400 rpm and the car shakes and misses, then back to 1500 rpm (which is as smooth as glass) then back to the 1300-1400 rpm (shaking again) however it gives me a 90 (PASSES the test) Which throws me off, why would it pass if it's missing?

oatburner99

Just an update guys I think I found the culprit. I checked the TPS, and found with the key on, the voltage was reading .002, however I was getting the 4.97 reference volts behind the electrical connector, which is what it's supposed to get. So I triedsetting the TPS to .99 (key on) and locked it down, however it's running to ground, because once I started the car, and I probed the green wire the voltage was ALL OVER the place, as the voltage fluctuated the RPMS's fluctuated. Also the check engine light would come on, then go off, come on, then go off. So the TPS sensor is grounding or open all the time, causing havoc with the computer. I'm assuming the computer is seeing lean, so it goes rich, see's rich then goes lean...and it's just all over the place. So a new TPS is in order tomorrow. I'm hoping that this will fix the problem. Also replaced the driver's side header gasket....I'll post up a picture. Didn't realize that the longtube primary tubes were soooooooo much bigger than the gasket holes...anyway 3 out of the 4 holes in the gasket were blown out.