View Full Version : limp mode..now misfire

06-09-14, 12:14 PM
Hey everyone
My '99 eldo 'Y' overheated and went into limp mode, said turn off engine, change oil now.
I fixed the leak, changed the oil, and the p0300 engine misfire detected won't stay cleared.
I took the 41-950's out and freshened them up but it still has the code because it still has a
rough idle. Is there anything else that needs to be done after limp mode has been activated?
There are codes for each cylinder but only the 0300 shows up. any suggestions will be much
appreciated, thanks Ed

06-09-14, 12:51 PM
The inboard scanner will only display P0300, not P0301-P0308. Have the codes pulled at a parts store.

06-09-14, 02:47 PM
Camel mode = overheated engine. Drops cylinders to lower temperature of combustion and move "cool" air through the dropped cylinders.

Limp mode = engine controls and ignition default to a fixed timing of 10 degrees BTDC due to some ignition or major emissions failure: Limp home.

Spark plug wires (AC Delco $110 set), coil checks/cleaning, ICM cleaning, ICM ground wire terminal cleaning. Wires/coils/plugs connected exactly as shown.

06-09-14, 04:44 PM
Thanks everyone, camel mode it is. Is there a specific way to check the coils? I have new plugs 41-950's (not installed yet), wires are 10k miles old. It is my own fault by not turning it off sooner. I hope it is not damaged too bad.
thanks Ed

06-09-14, 05:17 PM
You probably have done NO damage to anything. Probably didn't need an oil change either, but that's a GM safety recommendation.

Disassemble the ignition system, dismount the coils, make everything squeaky clean and check the ICM itself for cracks. Make sure that ground wire is properly connected and that the terminals are clean and tight.

The plugs come pre-gapped to .050". Pick up a small packet of anti-seize at a parts store and use a toothpick to work a dab into the first (bottom) 3 threads of each plug. Tighten to about 13 lb/ft. I like to use a smear of silicone dielectric ignition grease around the inside of each plug and coil wire boot.

EDIT: Where was the coolant leak ?? Any chance that coolant got onto/into a CKP or CMP electrical connector ? (CranKshaft Position, CaMshaft Position)................The diagram.

06-09-14, 10:13 PM
Did it spray coolant all over the engine or just out the over flow hose and down to the ground? Or did it not overflow at all?

06-09-14, 10:30 PM
the short hose in front and below the throttle body sprayed upward then overheated real bad and steamed
the engine fully. It wasn't dripping, but it was wet.
thanks everyone

06-10-14, 08:14 AM
You can remove (eliminate) the throttlebody hoses entirely and replace the remaining purge line with a length of proper sized reinforced fuel hose - from the hollow bolt/nipple directly to the surge tank nipple. Use small band clamps and be careful - that surge tank is old, brittle polyethylene plastic. (If it has not been replaced, it's on its last legs anyway.)

06-10-14, 10:16 AM
If the entire engine was wet and you still have a misfire, try spraying all the ignition contacts with WD40. Pull each plug wire and spray the inside of the boots (both ends). Pull the coils and spray both the top & bottom contacts (clean them with emery cloth if they show any signs of oxidation). Likewise the ICM contacts.

06-10-14, 11:48 AM
Thanks, how does one check a coil /coils for good,bad, or weak? Im cleaning the coil pack now. later Ed

06-10-14, 09:41 PM
Take the car to AZ or AAMCO or such and have them run the codes for you. As you can see by Sub's diagram, each coil services 2 cylinders. Their scanners (unlike out onboard diagnostics) will tell you which cylinders are misfiring as MC said in post #2. If you find 2 cylinders on the same coil misfiring, it's a pretty sure bet that the problem is the coil.


Another possibility might be the ICM.

06-11-14, 05:06 PM
You can remove wires from plugs one at a time - see which one (s) do not affect the idle speed. A bad injector, or bad connection to injector, will also cause a misfire and rough idle that mimics an ignition misfire