HELP!

[Trond]

I have a Roush 427R. The engine has been running good until now. It starts normal and is running ok until I put load on it. Then it starts to "sparkle" heavily with a lot of what seems to be misfire. I noticed that the little ball inside the MSD distributor cap had fallen out, and replaced the distributor cap with a new one. This did not help. I have also replaced the MSD AL6 ignition, the pickup and the coil without any help.

It also seems that the car runs almost normal when making the first pull after starting, and then the problems is increasing the more I drive. I have disabled the electric choke so this is not making any fuss. I have replaced the air filter with a taller version (4", original 2,5") but I can not see how this could result in the problems?

I am on the way to Nurburgring for two days of driving and I am desperat for good suggestions!

regadrs
Trond

 

[Steve]

did this occur when you replaced the air filter?

possibly you have increased airflow, and possibly improved air path into the carb, which might now mean your carb is fueling too low for the airflow, making the car run lean,

see if you can pinpoint when this started to happen, and what you "changed" at that time.
other thing to verify is exactly where you are with your timing. is your timing erratic.

 

[Jack Houpe]

Check fuel filters. SPF cars are known for lots of debris in the tanks. Sounds like your pump can't keep up with the flow needed.

 

[Jim Rosenthal]

I don't think changing the air filter would do this. I'm with Jack, it sounds like a fuel supply issue. You may have a clogged fuel filter or fuel supply line. Are the pumps powerful enough to collapse the inner lining of the fuel supply hose?

 

[Andy Green]

Hi Trond,
have you checked that the static igintion timing is correct? If it is too far advanced it will start & run @ part load, but will then 'sparkle' heavily (detonate) under full load

Regards
Andy

 

[Ron Earp]

I have a Roush 427R. The engine has been running good until now. It starts normal and is running ok until I put load on it. Then it starts to "sparkle" heavily with a lot of what seems to be misfire.

My first advice would be to stop replacing parts just to replace them. The engine ran fine with some of the physical aspects that have not changed - filters, fuel system, etc. so I'd not change them but diagnose them instead.

First place I'd start is with the ignition/electrical system.

• Check your timing as Andy says. Check it at idle and verify that it is a steady 10-15 degrees, whatever you like. Then run it up so the advance is all in and check that it is steady, 30-36 degrees, or whatever you like, but make sure it is steady and solid with respect to output. Regardless of what the fuel system is doing, if the engine will run to 3k (or wherever the advance is all in) and you can watch the signal with light or scope then the ignition system is probably fine. If you see it jumping around and not being stead then I'd be concerned about the dizzy/trigger. While you're messing around here make sure your alternator is putting out >12.5 volts at some decent RPM and that your battery is being charged. If there is any question about the MSD box go to the MSD website and there is a simple test for checking those out (white wire to ground, release and get a spark at the coil, or slightly different with purple/green wires on the box).
• Do as Jack and others have suggested - check your fuel system. You should have an inline gauge on the system anyhow, now would be a good time to install one. Make sure you've got the required pressure at the pump, after the filter, and at the carb. If you didn't change the carb between the time it ran fine and the time that it doesn't then it probably isn't the carb. But, if all the other things check out then you'll need to start thinking about the carb and what might have happened to it.

 

[Dave]

Have you checked your spark plug leads? Could be just a dodgy lead arcing out somewhere or open circuit.

 

[Ian Anderson]

Have you checked your spark plug leads? Could be just a dodgy lead arcing out somewhere or open circuit.

Start it in the garage or in the dark and see if you get cross arcing on the spark plug leads - sometimes you get quite an amazing spark show!

Last thought are your leads all going to the correct plugs?


Ian

 

[Trond]

Hi

Thanks for all input.

A summary:
I checked ignition system first. Checked the AL6 according to MSD instructoins, Ohmed the pickup without finding anything wrong. Then I discowered that the little ball (I think it is led) in top of the distributor cap was gone. Replaced with a new cap without any help. Then I changed both the AL6 unit, the pickup and the coil just to be shure everything was ok (I had an extra set already as spare parts) NOTHING HELPED. I also checked the timing twice, and both initial and advanced timing was correct. About 16 degrees on idle and 32 on top.

Then I checked fuel system. I have two Carter pumps pulling from each tank with a filter in front of them (both tanks have been out of the car and cleaned/checked earlier). Theese pumps deliver to two very big filters also functioning as swirl pots, before a Holly pump feeds the carb through a regulator. Pressure into the carb is 0,4 bar. Everything OK. I also checked the floaters in the carb, and that filling/closing/level was ok for both. Everything ok.

At last I now think I have found the problem. Changing back to my old spark plugs helped a little. Theese (Autolite) was replaced with Denso plugs that according to the compare lists is the same, and gap adjusted to 0,050 according to MSD recomendations. I dont know if the problem was wrong plugs or too high gap. After doing this I checked the timing again and found it to be wrong, about 5 degrees to low on top. I dont know how this can be, but maybe someone else knows if this can be caused by the plugs?

After a tip from one of you guys I started the engine in the dark, and also found on plug wire damaged sending sparks to the ground. This is now replaced, and I hope teh car will be running perfect on the Ring tomorrow. I will make one final check of the timing before I take out.

Any ideas about this beeing logical? I am no electrical expert and mostly HATE everything including any current!

Thanks for all your input!

Regards
Trond

 

[René]

keep it al in one part at the Ring...we want to go on the 30th this month...but my car need some fixing sadly...and the things I need are probably not there by then, so I have to go later or be very lucky
have fun there.

 

[David Sturch]

Trond,
What version of Autolite plug were you originaly using and what Denso plug did you replace it with. Running the wrong plug (resistance or temp range)can throw your engine mapping out. ECM data is also acquired through the plug.
Dave

 

[Ron Earp]

Trond,
What version of Autolite plug were you originaly using and what Denso plug did you replace it with. Running the wrong plug (resistance or temp range)can throw your engine mapping out. ECM data is also acquired through the plug.
Dave

I don't think he has an engine mapping as he doesn't have an ECU. Somewhere in there he said it was a carb car with MSD-6AL - about as simple as you can get.

Trond your ignition timing should not be different with different plugs. Are you sure you checked the timing at the same RPM? Do you know when your advance is supposed to be all in? When you checked timing, after you fixed your plug wire issues, was the ignition steady and solid?

 

[Grady]

I can only add what happened to me..several of the plug wires had bad jackets and melted spark plug boots. The silicon jackets got brittle and split. The solution was a new INSULATED wire set. HD NASCAR set made at a shop in Mooresville, NC. If you had 1 bad wire, you may have 3 bad. Also, it is easy to get the wires out of firing sequence...recheck the wires. It is something simple. The 6AL works or doesn't, on or off, when it fails it is dead.

 

[Howard Jones]

If you still find that things don't run correctly. Get youself a set of MSD plug wires. The make to fit type are pretty easy to put together.

I had a set of no name wires that I tried to use when I first ran the car. I had all kinds of plug wire issues. Broken wires internally, insulation breakdown at higher revs, weird stumble at different revs. Just bad running car.

A good friend of mine told me to throw that junk in the garbage and put together a new set of MSD wires. The car has run PERFECT since.

This is not to say that nobody else makes good plug wires. I do know that the wire set MSD recomends wire for a 6AL box will work without any drama.

 

[Rich E.]

I'm a believer in the KISS method. Our motors sound almost identical. I've got a 351 stroked to 427 with a Demon carb and MSD 6AL box. First I'd do like the others have suggested. When I got my car I wasn't getting proper fuel delivery. I cracked open the carb and found metal debris embedded in the gaskets on both sides of the carb body. Make sure your filters arent starving the motor due to poor flow from a clog. Also make sure your timing is correct. Did you by any chance move the distibutor at all? Also check that the spark plugs are the proper heat range and gap. I personally like NGK TR55's. Check the wires. They can hide alot of problems that seem intermittant.

.02
Rich.
fuel,air,spark and she'll run

 

[David Sturch]

Ron,
He did not post much info on his problem. I would not run an Iridium Plug on an older induction system. Older style Platinum Plug would be the way to go with the proper resistance and heat range. Wires and fuel are always the first thing to check, back in the day we used to make up our own wires with a spool of good quality 7-8 mm plug wire and quality ends. Running the wrong plug can mess up your engine.
Dave