Hi, my problem has me at a loss, if anyone can help it would be very appreciated. 1990 RS 305 TBI T5WC. Before the car fully warms up it runs great, but pretty soon (especially on hot and humid days) it starts running very rough and backfiring through the throttle body. If I give it any more than 20% gas it will sputter and backfire beyond being drivable. It has also been running a little hotter lately, without overheating, but could just be due to an extreme heat wave.

Fan is working fine. It isnt throwing any codes. Fuel filter is new. I have changed the distributor, coil, ignition module, cap, rotor, wires, and plugs. I ohmed out both fuel injectors ans they were exactly the same and in spec. I will be changing the tps soon but I doubt that is it.

Thanks,
Matt

 

You checked your timing recently?

Also if you have a timing light, you can connect it to the COIL, and flash both injectors as the car is running. You will see the spray pattern of both injectors.

GL

 

The injectors' spray looked good. I checked the timing (disconnected computer advance and everything), it was about 12* BTDC. I timed it back to 0* and it ran terrible, even worse and knocking. I put it at 6* and its still not as good as 12*. The guy I bought the car from 5 years ago said he had put a chip in it. I don't know anything about the chip except that I know sometimes they have you advance the timing when you put them in. Otherwise I'm still at a loss.

 

When was the last time you changed the O2 sesnor?

 

not too long ago it should be ok. i also drove it with the sensor disconnected and it is still bad. It really runs ok until it warms up then its undrivable. So maybe esc? i might change all the plugs and wires again maybe theres a bad one. also, it never throws codes, the check engine light is working, but even when i disabled the computer advance and disconnected the o2 sensor it never throw any trouble codes.

 

That is odd what your PCM is doing. It should atleast throw a code 12. You sure your jumping the right pins and following the correct sequence?

Also have you checked your map sensor? I'm gonna assume your having closed loop issues.

do this first
Check the coolant temp sensor in the front of the manifold. The 2 wire one that sends signals to the PCM.

 

Maybe the timing chain is stretched. I had one to do that on me and gave the same problem..When it warms up, pull #1 plug..put on TDC and check your rotor in the distributer and see where it's pointed at..should be at #1 wire. Hope this helps..God Bless US All...John

 

ok i got it to throw a code and the trouble code system seems to be working right. But how can I check my map sensor? or the coolant temp sensor?

And that could be a good idea about the timing chain, I will check it out too.

Thanks for all the input btw

 

I doubt the timing chain is boned. Normally with timing chain problems, you have just one flat spot, then when the chain tensions, itll run good after the sputter miss backfire. (btw you can check it though, as that is one thing i reccomend with almost all these cars, its as simple as pulling the cap off and turning the crank pulley back, then forward, an remember all chains will have a slight delay until its tensioned.) (side not if you have serp setup, you can just grab the serp belt and push pull to turn the crank, if your strong enough)


The 2 tests are really simple, but you need a few tools, Multimeter, and manual hand vac pump. (or you could run the car and rev it or have someone rev it testing the MAP). Ill have to get back to you on the exact specs on both sensors. You can do a search on testing both of them. Sorry for not being able to put them up right now but im tired, and ive had a long night.

 

BTW stubby, no offense is meant by me dismissing the timing chain idea. (yes i know if the chain is uber stretched it will cause ignit timing issues, but you have other issues you notice first)

 

Check the fuel pressure when hot & running bad. Spec for TBI is 9 to 13 psi. There isn't a port for it, need to add one to the feed line at the frame to engine flex lines. The feed line is the larger of the two.

RBob.

 

I bet its the coolant temp sensor on the front of the intake. sounds like it is sending the pcm that the engine is cold when the motors actually hot. A new one wouldn't hurt. I would test it first (if you have a repair manual with the voltage specs. and a mulimeter) when the engine is cold it should put out a certain voltage. As the engine warms the sensor will gradually increase or decrease(have to look up the specs) the voltage telling the pcm what to do. good luck

 

I got my crosshairs on the CTS, but you got to test things. Makes no sense throwing money at it and its ok.

 

Ok I think I got it and its stupid. a faulty #5 spark plug wire. I ohmed it out and it was over 2000000 ohms. its strange that it ran so well at idle and cold temp and only acted up when hot. I returned it and they exchanged it. after all that it was something to simple. thanks for all the input though everyone.

Thanks,
Matt