I have a 1990 RS 305TBI stick shift.

I started her up today for a quick 20mile errand. everything fine till car heated up.

Car heated up a little over the 220 mark before flipping my manual fan switch, i usually flip it before 220 but i forgot. Never let this happen before.

On the freeway once the car hit operating temps, i notice hesitation and stumbling when accelerating, kind of like a misfire, also a power drop, felt like i was towing something. Exiting the freeway I noticed my oil pressure dropped to 0 when i came to a full stop. When accelerating the oil pressure wouldnt go higher than 15-20. Decided to head home.

Got off the freeway exit on the way home, i used the tranny to slow down, when downshifting, the car would backfire as the rpms drop, not a loud boom, but a few pops. Out of curiosity i did a second gear pull, as the car slowed, the exhaust let out a few wet sounding pops. Its only when slowing from higher rpms. When i got home i noticed the exhaust was making a putt putt sound like its cammed or something

New sparkplugs, wires, oil/filter, tranny fluid and cleaned the air filter. All under 150 miles ago. I also should note the oil pan is leaking and car has no cat (previous owner removed it.) Only mods to the car are 3 inch pipes to flowmasters and a cat delete

Any input on where to start looking is greatly appreciated. I did a little reading and a thread with a somewhat similar problem mentioned checking the cts, tps, iac, and egr, and another thread mentioned bad cam bearings could cause a drop in oil pressure when warm. Any of this sound relevant to my problem? Thank you

 

Just got done testing my cts. Not sure if the car has to be on or off when testing so i did both. The car was completely cold while testing

With the car off and my meter set to 20k, it read 3.35, not sure if this translates to 3,350

With the car on and my meter set to 20k, it read 3.17

From what i have read, the cts should be within spec.

I should also note when i started the car up it was idling perfectly despite how bad it was yesterday. However this is on cols start and the problem started when the car warmed up

 

Any help is appreciated. This is my daily driver and i have no clue what the problem might be or where to begin searching for a problem.

 

Further research is leading me to believe the problem could be the ICM. Im gonna replace this and throw on a new cap and rotor. Hopefully this solves my problem.

 

Up for a whole day and no one has any input? Everyone must be out celebrating veterans day today. Or maybe noone wants to go through and read my essay of a post.

Anyways. I just realized, the ICM would be the culprit if i were only experiencing the power loss, putt putt exhaust and the sputtering. But would a faulty ICM cause the car to run so rich and cause it to backfire?


Please help. I need my car for work, and my buddy is only able to loan me his car for a few days

 

CTS will make it run awful.

If the spark fails, the fuel doesnt burn, and gets dumped into the exhaust.

 

So it may very well be the ICM. Im going to do a little testing around the distributor tomorrow to see what else may need replacing besides the ICM.

Thank you for your input. I felt like i was writing in a blog or something. People reading but only i can post

 

You may also want to look at the pickup coil and your ignition coil.
You can test the coil using your multimeter and some diagrams floating around the net.
Both components can change their behavior when warmed up and behave normally while cold.

 

The ICM will affect timing, and timing being off could be an issue that's causing some of the backfiring. I know Autozone has the capability of testing ICM's provided they have the right connectors. You can test the ignition coil and pickup coil with an ohmmeter.

All that being said, I'd be concerned with the drop in oil pressure.

 

Yeah the oil pressure thing is weird....

What are your alternator volts? Weak electricals = weak spark and maybe every other indicator will proportionally fail as well...

What is the RPM when it's running badly with no oil pressure? Low RPMs=low oil pressure. It will probably mean not much voltage either just due to very low RPMs.... as if it's chugging at 300-400 RPMs or something. That will cause VERY low oil pressure readings.

It seems very weird that all of this would happen at once, and I dont think for a second this has anything to do with the temperature. It's possible... but... I dont think it's connected given what you've shared.

 

Unfortunately my tach doesnt work, but im pretty sure when my car starts acting up the idle drops really low.

I been reading up on pressure drop when the car is warm and just about everything that comes up is about the cam bearings

 

My alternator and battery are both brand new, about 2 months old. My dash, although not accurate, reads really high at just under 18 volts so i know everything is getting sufficient power.

Been a little busy with work so i havent had a chance to get back under the hood. Im gonna do more testing on the distributor on my day off

Would it be a good idea to buy a complete reman'd distributor to replace the old one i have instead of just replacing parts? For the price of a cap rotor and icm, i could just get a reman'd one.

 

cap and rotor are like $15 together, ICM is what... $25? Any distributor worth $40 I would stay away from... Replacing the whole distributor is more work as well.

Im still confused about the oil pressure thing...

 

My local autozone has cap and rotor listed at 25 and icm at 50. For 75 i still have the pickup coil, ignition coil, and the shaft to worry about, the distributor im looking at is a duralast for $100. I said "for the same price" in my last post, should've said" for a bit more"