Got towed home yesterday need engine help

[Silverstreak02]

I took a long drive yesterday in the Cobra and it was running well until I was almost to the restaurant. As I pulled out from a stop sign it hesitated slightly and then smoothed out for another mile or so. At the next turn it bogged down pretty bad as I accelerated. I made it to the restaurant, but had to get towed home after that. It still runs, but idles roughly and the tachometer bounces between 600-900. Every few seconds the tachometer jumps to almost 2000 without any change in the idle. I have an Explorer motor with a Holley 570 and Max fire distributor. The setup has about 1800 miles and has worked perfectly until now. I've checked the following without seeing anything wrong.

1. I inspected the three and two pin connector at the Mallory Max fire.
2. I removed the cap and top cover of the distributor and inspected the cap, rotor and PCB.
3. Removed the tachometer signal wire at the distributor and started the engine. The tachometer still bounce some although the signal wire was disconnected. Power and ground was still connected.

The engine runs and idles, but it is rough although it smooths out for a few seconds every now and then. Does anyone have a suggestion of where I should look next? Thanks for the help.

Jeff

[WardL]

Just so you don't do a lot of work before checking, you ight check to see your fuel doesn't have too much water. If the fuel is cloudy, it is bad. Ethanol in the fuel (E10)will soak up much more water than fuel with no ethanol (E0) and run fine. But everything has a limit and when too much water gets into your gasoline, the water starts to drop out and settle to the bottom of your gas tank. Cloudy fuel or fuel with little dropplets is the best indicator of a problem. The water is heavier and sits on the bottom of the gasoline.

[Caprimaniac]

The MAX fire does have some circuitry in the cap? Maybe some ghosts there? Have a look at the instructions, maybe there's a way to test the dist.

Might be fuel realted as well... Floats or other.

[Gaz64]

A faulty tachometer will cause your issue, especially if the needle still moves with the signal wire disconnected.

Don't discount a tachometer as the cause for intermittent spark.

[Silverstreak02]

Originally Posted by Gaz64

A faulty tachometer will cause your issue, especially if the needle still moves with the signal wire disconnected.

Don't discount a tachometer as the cause for intermittent spark.

The tachometer needle does bounce around with the engine running even though the signal wire is disconnected. I keep thinking the tachometer is a clue, but without a direct connection to the distributor I don't see why. It is an electronic tach from Speed Hut. The engine still runs rough with the signal wire disconnected.

[trularin]

Remember the three 'F's.

Fuel
Fire
Function

Check for each.

[Silverstreak02]

I didn't have much time tonight, but I checked the resistance of the coil (less than 1ohm) and looked at connections again. I started it and it was more difficult then usual, but did start and idle roughly. I let it idle for a minute or two and shut off all the lights in the garage to see if anything was arcing or sparking. I didn't see anything so I gave it some gas. Within about 20 seconds it backfired out the pipes and stopped running. I tried to start it again, but no dice. It will fire for a split second if I pump the gas, but that's it. I have a hard fail of something at this point, but no more time to work on it tonight. I'll look more tomorrow.

So far I've avoided removing the distributor to check the gear for a reason. My damper doesn't have any timing marks on it so it's hard to get it timed correctly. The last time it was set on the dyno by my tuner. I think I'm getting very close to either doing that or buying another coil. I hate troubleshooting by shotgunning parts. I talked to Mallory and they said they would test the distributor for free, but it would take 2 to 3 weeks. If I pull it I may send it to them for testing. I have a few other things to check before I do that.

Jeff

[WardL]

When was the last time you gassed up?

[Gaz64]

Originally Posted by Silverstreak02

I didn't have much time tonight, but I checked the resistance of the coil (less than 1ohm) and looked at connections again. I started it and it was more difficult then usual, but did start and idle roughly. I let it idle for a minute or two and shut off all the lights in the garage to see if anything was arcing or sparking. I didn't see anything so I gave it some gas. Within about 20 seconds it backfired out the pipes and stopped running. I tried to start it again, but no dice. It will fire for a split second if I pump the gas, but that's it. I have a hard fail of something at this point, but no more time to work on it tonight. I'll look more tomorrow.

So far I've avoided removing the distributor to check the gear for a reason. My damper doesn't have any timing marks on it so it's hard to get it timed correctly. The last time it was set on the dyno by my tuner. I think I'm getting very close to either doing that or buying another coil. I hate troubleshooting by shotgunning parts. I talked to Mallory and they said they would test the distributor for free, but it would take 2 to 3 weeks. If I pull it I may send it to them for testing. I have a few other things to check before I do that.

Jeff

This may be a silly question, why has the engine got no timing marks?

Who built the engine without reliable timing marks?
How did the tuner know what timing the engine is running?
Did he alter the timing while plotting for max torque through the useable rpm band?

Remove the rotor button and check there is no carbon tracking where it goes on the shaft.

[tcrist]

Try replacing the rotor or at least check to see if it is working. Make sure that your coil is working and then check to see if you are getting fire to the plugs. I have had 3 go bad before. Two Fords and one Chevy.

Just a thought.

[Silverstreak02]

Originally Posted by WardL

When was the last time you gassed up?

Last Thursday

[Roger Bray]

Please understand that I am by no means an expert.
However, I just resolved a problem similar to yours.
It turn out to be a bad coil.
When checking to see if you have spark do it in a dark garage to make sure it is blue not yellow. Also crank the engine for several seconds to make sure you continue to get good spark. This turned out to be my issue. The spark was weak and after a few seconds I did not get any spark at all.

Again, I'm just a hobbyist so take this for what it worth.

Roger

[Silverstreak02]

Originally Posted by Gaz64

This may be a silly question, why has the engine got no timing marks?

Who built the engine without reliable timing marks?
How did the tuner know what timing the engine is running?
Did he alter the timing while plotting for max torque through the useable rpm band?

Remove the rotor button and check there is no carbon tracking where it goes on the shaft.

The motor is from a low mileage Explorer from a salvage yard. I bought a new damper and many other components to convert it to a Mustang front dress and carb. The damper was from Ford Racing and had very light indents in the finish that I used to set timing to get it started. They were extremely hard to see so I bought one of those tapes and installed it. Before I put the tape on I wiped the damper with acetone to clean it and what marks that were there disappeared. The tuner adjusted the timing on the dyno and I'm not sure exactly how he did it, but it seemed pretty good for the first 1800 miles. I've had the rotor off already, but will remove it again to look closer. Thanks

[Silverstreak02]

Originally Posted by Roger Bray

Please understand that I am by no means an expert.
However, I just resolved a problem similar to yours.
It turn out to be a bad coil.
When checking to see if you have spark do it in a dark garage to make sure it is blue not yellow. Also crank the engine for several seconds to make sure you continue to get good spark. This turned out to be my issue. The spark was weak and after a few seconds I did not get any spark at all.

Again, I'm just a hobbyist so take this for what it worth.

Roger

How exactly do I do this? do I only need to remove one plug and crank it over with all the other plugs installed and connected or do I need to disconnect all the other plugs to keep it from starting(assuming it might start)?

Jeff

[Roger Bray]

I'll tell you what I did, but it would be wise to verify my technique with some of the more experienced people here on Clubcobra.
I removed one plug and let it lie on the intake manifold so the plug would be grounded. I tested the manifold with my volt meter and it was grounded.
The other plugs were left intact. I also took a video of the plug while I was doing the test so I could get feedback from other members.

It took me several days to track down my problem.... frustrating at times, but it was a great learning experience.

[FOMOCONUT]

Try another COIL, any coil will do. SPF #2773 Jerry

[emm427]

Originally Posted by Silverstreak02

How exactly do I do this? do I only need to remove one plug and crank it over with all the other plugs installed and connected or do I need to disconnect all the other plugs to keep it from starting(assuming it might start)?

Jeff

Go to Napa or any parts store and ask for an inline spark tester! Lot safer! The last thing you want is to have the fuel vapor pushed out the empty spark plug hole and light with a plug open to the vapors. Just a thought on the safe side, you wouldn't be the first guy to burn down his garage. Tim

[Silverstreak02]

I checked the gap on the plugs tonight. They are .054 which is what they are supposed to be according to my Chilton manual. I re-installed the plugs and distributor in anticipation of trying it one more time. Due to the rain tonight I'm going to have to wait for that. If it still doesn't run I may try one of those inline spark testers before I pull the trigger on either replacing the coil or have the distributor tested.

Jeff

[Gaz64]

I would regap the plugs to about .045.

Large gaps bring on failures elsewhere in the ignition system.

How is your rotor button/distributor contact button relationship?

[67JET]

This may sound odd but when i have issues such as yours and can't find an obvious problem i change out all the plugs first. I had a dealership tell me once that i had a bad motor with no compression and that is why it wouldn't run. After talking with my Dad and calling him crazy a few times i called the dealership and told them to put new plugs in it and try it again. Then they called me crazy a few times and said if your paying we will do it (i was out of town and couldn't do it myself). They called me back and said it was fixed and didn't charge me labor just for the plugs. My experience was just like yours - run great-run bad-stop running. Maybe you can just check them but you can buy a cheap set of plugs and know for sure.