89 Formula 350 TPI - Car runs fantastic until it gets hot and goes into closed loop, then misses and runs rough. When it gets hot it gets real hot, real fast. Only mods are SLP intake runners and ported, matched plenum.

New parts include, 19 lb injectors, fuel pump, fuel filter, plugs, wires, rotor, cap, ign module, Ign coil, dist and all sensor pigtails, IAC, TPS, O2, thermostat 180 degree, vacuum hoses replaced, EGR valve, IAT, and many other parts I'm sure I've forgot. Had a fuel problem as well which is solved. Bought the car 2 years ago and it's never ran right.

Car throws no codes. It's to the point now that it's so depressing it's comical. Ahhhh, but those first five minutes, before it heats up are magical.

If you have a shred of decency...please help.

Thank you

 

bump

 

When does the miss occur, ie does it miss at all RPM's and loads or only under certain conditions?

Does it have the stock chip or a modified one (if your not sure, check it in the ECM).

Is the check engine light working, ie does it come on with ignition on before your fire the engine?

Are you sure your timing advance is set correctly?

Paul T.

 

Thanks for the reply. The miss occurs at all RPMs. I verified that it has a stock chip. The ECM was replaced by the PO but it is the correct one and it is AC Delco. Doesn't mean it's good though. The check engine light does come on before start. It does not show any codes though. I unplugged the EST and set the timing to 6 degrees BTDC, while the cars in drive as the under the hood label states. I then re-connect the EST. I believe that to be the proper method. Please let me know if that's incorrect.

 

i never set my timing with car in drive but not sure if that changes things too much or not.

balancer could be off so true timing remains unknown, but only way to see for sure is with tunerpro rt or other scanner

 

Spend all day working things through...still missing in closed loop only.

 

Once it's in closed loop and it misses, unplug the O2 sensor and see if it stops. This will determine if its a closed loop thing or just temp related. If it goes away try a new sensor. I have seen many shorted lean and flooded the engine rich, or shorted rich and starved the engine of fuel. If its temp related, you will have to determine if it's ignition or fuel. Also you didn't say if it was one cylinder or more.

 

A couple of things that I can think of is first check for a vacuum leak at the runner gaskets. Also make sure the runners are on the correct side it maybe possible to install them on the wrong side and give yourself s vacuum leak. Sometimes a vacuum leak will not make an engine run bad until it goes into closed loop. Also if your leak is near the runners that feed cylinders 2,4,6,8 your O2 sensor may not sense the leak, depending on its location. The second is possible MAF sensor. Try tapping on the sensor with a screw driver handle while the engine is running and watch for the engine for flutter or miss. I had a 84 v6 Camaro that was missing with no codes I changed every part of the ignition and cleaned the injectors and it still ran like crap. Ended up a buddy of mine told me to tap on the MAF sensor and that was it.