'94 stumble when cold
06-14-2017, 12:16 AM
#1
Instructor
Thread Starter
'94 stumble when cold
Hello,
You can see my mods in my sig that way everyone knows where the car stands. I've got the tune pretty lined out and the car honestly runs great throughout the rpm band except after just starting. If I start up the car (even if the temp is 180 degrees still) let it idle until closed loop and go drive it, under any sort of load it stumbles and bucks at any rpm. After driving it for 5-10ish minutes on the highway, it runs smooth as can be with no issues. Except it doesnt like getting a lot of throttle under load under 1500 which I could easily contribute to the cam. Also, it does it in open loop as well. If I start it and then drive without letting it get into closed loop first any sort of load over light acceleration results in the same symptoms. That leads me to believe it is not 02 related. Being the it runs great after 5-10 min I doubt it's a fuel pressure problem. My opti is brand new and isn't throwing any codes. Ive got all new AC delco plug wires and NGK plugs. The only thing that I can think of is the ICM and the coil. They are both the factory units (my opti was too). I just dont want to start throwing parts at it without a solid basis first. Also, I am running in Speed Density so the MAF is out of factor. Thoughts?
Thanks!
Colton
You can see my mods in my sig that way everyone knows where the car stands. I've got the tune pretty lined out and the car honestly runs great throughout the rpm band except after just starting. If I start up the car (even if the temp is 180 degrees still) let it idle until closed loop and go drive it, under any sort of load it stumbles and bucks at any rpm. After driving it for 5-10ish minutes on the highway, it runs smooth as can be with no issues. Except it doesnt like getting a lot of throttle under load under 1500 which I could easily contribute to the cam. Also, it does it in open loop as well. If I start it and then drive without letting it get into closed loop first any sort of load over light acceleration results in the same symptoms. That leads me to believe it is not 02 related. Being the it runs great after 5-10 min I doubt it's a fuel pressure problem. My opti is brand new and isn't throwing any codes. Ive got all new AC delco plug wires and NGK plugs. The only thing that I can think of is the ICM and the coil. They are both the factory units (my opti was too). I just dont want to start throwing parts at it without a solid basis first. Also, I am running in Speed Density so the MAF is out of factor. Thoughts?
Thanks!
Colton
Last edited by CMiller95; 06-14-2017 at 12:17 AM.
06-15-2017, 10:26 AM
#2
Zen Vet Master Level VII
Double check your coolant sensor. My quick guess is that your sensors is sending false readings to your computer. Your engine thinks it is cold when it is warm so your computer runs it rich causing the stumbling.
06-16-2017, 04:05 PM
#3
Le Mans Master
Just wondering, since you have capability of changing the tune and flashing the PCM, do you have a scanner to look at the OBD1 data. That would be helpful by looking at fuel trim, O2 voltages and all the other just to see if you can see a change between the two conditions.
Also if the temp sensor was bad you would see "not normal" digital temperature readings in your speedo. The PCM sees the same indication.
The symptoms are almost opposite of a bad opti where it usually runs poor when it's hot.
For the heck of it, check for any plug or coil wire sparking to anything when cold. Rev the engine and look at the plugs and around the water pump where the coil wire is. I know it's all new but who knows if there is a pinhole somewhere.
Also if the temp sensor was bad you would see "not normal" digital temperature readings in your speedo. The PCM sees the same indication.
The symptoms are almost opposite of a bad opti where it usually runs poor when it's hot.
For the heck of it, check for any plug or coil wire sparking to anything when cold. Rev the engine and look at the plugs and around the water pump where the coil wire is. I know it's all new but who knows if there is a pinhole somewhere.