Author Topic: Engine run-on (Read 4861 times)

Yelby · « **on:** June 25, 2014, 10:56:35 AM »

Newly rebuilt 2.3 set to 20deg advance per sticker. New Weber 2 barrel carb with electric choke. What would cause engine to run-on after turning key off after cruising at 55-65 for 30 to 45 minutes?

74 PintoWagon · « **Reply #1 on:** June 25, 2014, 11:21:55 AM »

Idle set to high?

..

Pinto5.0 · « **Reply #2 on:** June 25, 2014, 11:32:02 AM »

My 60K mile 2.3 does it after a tune up including wires, gaskets & an NOS carb. I have the timing down to 14 degrees & it still does it. I've tried to solve it since last year to no avail.....

74 PintoWagon · « **Reply #3 on:** June 25, 2014, 11:34:58 AM »

I've never seen timing cure that, but this is the cure..

Pinto5.0 · « **Reply #4 on:** June 25, 2014, 11:54:35 AM »

My bad, I also have knocking & pinging during acceleration which is why my timing is backed off. I'm still pinging ay 14 degrees just not as violently. I'm getting hot spots in the cylinders even with the timing backed off & those are causing my run on.

A solenoid will help cure the run on but that pinging is still taking it's toll on my pistons & valves.

74 PintoWagon · « **Reply #5 on:** June 25, 2014, 12:02:32 PM »

That's not good, gotta run better gas or lower compression, might fatten it up a tad too that helps to cool it down a bit and kill some of the rattle..

Pinto5.0 · « **Reply #6 on:** June 25, 2014, 12:39:05 PM »

Quote from: 74 PintoWagon on June 25, 2014, 12:02:32 PM

That's not good, gotta run better gas or lower compression, might fatten it up a tad too that helps to cool it down a bit and kill some of the rattle..

Nah, I'm taking the easy way out & swapping the engine, distributor, ignition box & going to a new Weber 38 in hopes that cures the problem.

74 PintoWagon · « **Reply #7 on:** June 25, 2014, 12:46:03 PM »

Quote from: Pinto5.0 on June 25, 2014, 12:39:05 PM

Nah, I'm taking the easy way out & swapping the engine, distributor, ignition box & going to a new Weber 38 in hopes that cures the problem.

Oh ok...

Pinto5.0 · « **Reply #8 on:** June 25, 2014, 01:18:37 PM »

Quote from: 74 PintoWagon on June 25, 2014, 12:46:03 PM

Oh ok...

I've spent at least 50 hours over 2 years chasing this problem. I'm just changing EVERYTHING to eliminate all variables. I'm thinking I either have a bad head or intake gasket or god forbid, a head crack, Whatever is giving me the hot spots is going to ruin this 60K mile engine if I don't get it out & go though it.

dick1172762 · « **Reply #9 on:** June 25, 2014, 03:22:44 PM »

Spray water down the carb with the engine running. That will help get rid of the carbon on the head. Don't use a water hose! With a spray bottle, you can't put to much down the carb. Works for me.

mallen · « **Reply #10 on:** June 25, 2014, 04:34:10 PM »

I need a rack and pinion for my 1979 pinto.. I need to measure the input shaft .. Is it the length of the shaft coming out of the rack??

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amc49 · « **Reply #11 on:** June 25, 2014, 05:09:27 PM »

Where did that come from?

On after run, carbon glowing in chamber does it, it then needs fuel/air to keep running, and why you use a solenoid to drop idle setting to a totally closed throttle bore when key turned off. Richen jetting up and often it can disappear. If you have too much compression for the fuel octane used then give it up. In a few weird instances alternator residual output as motor spins down to die can do it too. Usually just having the solenoid on the throttle fixes it instantly. Can't after run with no fuel/air.

On water injection, use an expensive system with a variable setting computer, you don't wanna know what water injected motors look like inside when run with a bit too much water to them. The steam pitting of cylinder walls can utterly destroy them. Seen it more than once.

Pinto5.0 · « **Reply #12 on:** June 25, 2014, 05:24:04 PM »

Yeah but the hot spot is still causing pre-ignition under throttle which will eventually do serious damage if I let it continue.

74 PintoWagon · « **Reply #13 on:** June 25, 2014, 06:02:19 PM »

Quote from: Pinto5.0 on June 25, 2014, 01:18:37 PM

I've spent at least 50 hours over 2 years chasing this problem. I'm just changing EVERYTHING to eliminate all variables. I'm thinking I either have a bad head or intake gasket or god forbid, a head crack, Whatever is giving me the hot spots is going to ruin this 60K mile engine if I don't get it out & go though it.

Well, from the sound of it you may have something internal doing this probably time to dig into it, keep it up and it will be destructive for sure..

fozzy · « **Reply #14 on:** June 25, 2014, 10:29:50 PM »

Just some food for thought here..maybe the combustion chamber is running too hot and here is my theory..

One of the guys that I work with does alot of tuning, mostly newer GM vehicles. He uses HP tuners. His wife started complaining about how her vehicle was running. He initially dismissed it until he drove it and sure enough it was running like a bag of crap. He started testing and data logging it and other vehicles and came up with the reason. Ethanol.

The percentage of ethanol in the fuel was far higher than advertised wich throws off the stoichometric formula. He says "that the fuel mixture needs to be fattened up 4% for normally aspirated and 6% for turbo cars 9 (as a starting point).
Anyone using a wide band should shoot for 12.4 normally aspirated & 10.6 for Turbo cars"
Keep in mind that is what he found with the local fuels. He also managed to find out that Locally both Chevron and Co-Op do not use Ethanol.

Here is a link to some more info on the subject:
http://www.hotrod.com/techarticles/engine/1307_wideband_oxygen_sensor/

About 3/4 the way down the page there is a chart that shows the A/F ratios of various fuels.

74 PintoWagon · « **Reply #15 on:** June 25, 2014, 10:59:47 PM »

That Ethanol sure is a pain, used to be able to leave a car sit for a week and it would fire right up, now let it sit for 3 days and it hardly wants to start..

amc49 · « **Reply #16 on:** June 27, 2014, 03:05:59 AM »

I as well forgot about the ethanol having to run it in mostly PCM cars now. It will do exactly as said there, ethanol A/F ratio around 9/1 vs. gasoline at 14.7/1. And getting a standard percentage??? Good luck with that, here it is supposed to be E10 but they commonly cut more to be closer to 20%, they get the ethanol for a song due to federal subsidy on it making it cheaper than gas. Cutting it more makes more profit and no one checks the fuel percentage at all. Around here the car dealers commonly check the tank percentage at repair time and if warranty repair they disavow it and you have to pay out of your pocket. Seen news stories on it. The mileage varies all over the map now depending on the fuel in last fillup too making checking mileage closely virtually impossible.

If you live in an EPA non-attainment area there is no fuel choice, you are stuck with the stuff.

74 PintoWagon · « **Reply #17 on:** June 27, 2014, 07:58:14 AM »

What grinds me is that I'm in a totally smog exempt area but we're still stuck with this skunk pi$$..

amc49 · « **Reply #18 on:** June 28, 2014, 02:08:42 PM »

The Webers used on these did come with those solenoids back in the day........... ...........dun no if you can find them now........... ...

I used to not have one on my '74 but was forced to put it back on when they slowly dropped the gas quality in the '90s to totally stop mine from doing the same.

blupinto · « **Reply #19 on:** June 29, 2014, 12:52:16 AM »

Is it dieseling or not shutting off at all? My '74 wagon dieseled after the car was shut off because of a bad carburetor adjustment (not naming names)... problem solved after I took the car to a carb shop. Ruby RedHot's engine would NOT shut off after her original voltage regulator was replaced (nothing wrong with it) with one for a V8 at Carlisle. I even took the key out of the ignition! Needless to say, the original VR was put back in and I haven't had that problem since.

amc49 · « **Reply #20 on:** June 30, 2014, 12:29:21 AM »

Like said there was an alternator issue of some sort that could do it as well, there was a mod back in the day in one of the magazines (forgot who) that dealt with a slight rewire that fixed it. Had to do with residual field in alt then powering up spark when key cut off thinking. Or something close.

What gets really weird is when it does it and crank starts running BACKWARDS, don't see that everyday...... ......the AMC race cars used to do it and sometimes then damaged rad hose when the flex fan blades flexed out too much backwards. Since all were MTX we just started killing the key and dropping clutch to stop it. Really strange to see exhaust smoke come out the intake though.

Starliner · « **Reply #21 on:** July 19, 2014, 09:18:59 AM »

amc49 has it right.
So focus on doing these things:
1. Make sure your idle is under 900 RPMs after it is off the choke.
2. Run your gas down. Fill it up with premium. It really does not cost any more if you get rid of spark knocking since it will run more efficiently and improve the gas mileage. Driveability will improve and your right foot will be rewarded.
3. Make sure the engine is not running hot. Good cooling system and the timing should not be retarded. Pull your distributor cap and place 4 drops of oil on the felt underneath This is what lubricates the mechanical advance. Add 2 drops every 6 months there after.

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Author Topic: Engine run-on (Read 4861 times)