My 1991 350 TPI with 130k miles was running just fine and then i noticed a sudden tone change in the car. I looked at my gauges and they were all fine but when i went to pull out of the bank, the engine acted like it was misfiring on a couple of cylinders. I got it home and checked the wires and changed the plugs to no avail. The car still idles kinda rough, but the misfire is most noticeable under the slightest acceleration or load (going uphill).

I don't know if this is the ignition module, the pickup coil, or something else spark related or if it is the Coolant Temperature Sensor. I don't think it is the CTS but someone on another post said that it was. I haven't changed the fuel filter, but i really dont think that is the problem...Like i said it was running just fine and it just suddenly changed while i was idling.

Any help would be greatly appreciated as i am ready to put a new motor in and i need to get this fixed asap.
Thanks,
Brandon

 

Unplug your MAF and see how it runs.

 

Nevermind. You don't have one!

 

I am having the same problem on mine right now. Check your plugs and wires...make sure wires are not hitting the headers/manifolds. You might also check the resistance of your injectors to see how they look. Is it doing it mostly in closed loop or all the time? If it is closed loop, check and possibly replace the O2 sensor.

So far I have replaced wires, O2 sensor, went back to my stock coil and none of this helped. This is when I checked injector resistance and found that my #7 injector is pretty much dead (0.66 ohms).

 

I assume that you connect your meter across the pins on the injector (after removing the electrical plug of course). What SHOULD the resistance be??

 

It seems that it is only occurring in closed loop. If i let it cool down and start it right up and get out on the road it will haul *** for the first minute. Then when it goes into closed loop it starts acting like it is missing, but would an o2 sensor really cause that to happen? I might just replace the sensor and see what happens.

 

yes it will...the O2 only operates in closed loop and under part throttle. when it starts, if you go WOT...does it still do it or does it go away?

 

yes...take the connector off and with the car running, probe the pins in the top of the injector. resistance should be no less than 12 ohms IIRC. maybe someone else will chime in and correct me if i am wrong.

 

I have the Opposite Problem. Runs great when accelerating but goes "jerk-jerk-jerk" when holding steady throttle at 30, 40, 50 etc mph. What's that all about? New AC plugs, wires, cap/rotor O2 sensor. Weak ignition module? How do you check current/resistance at the injectors? Just remembered----new fuel filter too. How does one check fuel lines for obstructions? 1989 Formula 5.7 TPI