My 500 Wedge is Down on Power

[Charger_Dart]

I have tried a lot of things, but just can't seem to find what is just not right on my engine. I have a Mopar Performance 500 wedge crate motor P5007628AC that I bought about 6 years ago from a Dodge dealer. When the engine was new, it ran good and had tons of torque. Now its a dog that can't get out of its own way, and I need some help on what to look for. I have never had the engine apart, and maybe that's my next step? I sure hope not... The specs on my engine combo are:

MP 292 / 509 hyd cam
950 double pumper Proform Carb
Edelbrock RPM dual plane intake
Factory HP manifolds - TTI exhaust system
Stage V cast iron heads
new Accel distributor with new Firecore 50 wires, XR5 plugs, MSD 6AL Box & MSD Blaster coil

Engine now pings under WOT when it did not before. Settings I have currently -

Timing is 18 degrees initial, 36 total
cranking compression is 160 psi in 6 cylinders and 170 psi in 2
Air Fuel meter reads 13.5 at idle, 12-13 cruise, and 11-12 at WOT
Only 5 inches of vacuum at idle - 950 rpm's

Rough idle, but I think that's normal with that cam.  Auto tranny with a higher then stock stall so rpm's don't drop too much from Park to Drive.

What do you guys think? 

[firefighter3931]

How do the plugs look ? Maybe they're fouled ?

The WOT afr's are rich so that will make it down on power. It should be high 12's to low 13's

The timing looks ok but it's interesting that the engine is only making 5 hg @ idle....that seems low. 

I'd also have a look at the power supply to the MSD box. They need a good 12V at all times to run properly.


Ron

[Charger_Dart]

Hey Ron, the plugs are pretty black, but don't appear to be fouled. I had a hotter plug in there before the XR5's but that made the pinging worse.

The MSD is wired to the battery alternator post. The alternator is a 1 wire unit from Powermaster.

I was running a 850 Holley and the AFR at WOT was a a little better. I was hoping a carb swap would help but the engine ran the same. 

[firefighter3931]

The cruise and wot afr's are too rich....idle is fine. Luckily you have a wideband to take some of the guesswork away 

I'd start with a fresh set of plugs and adjust the jetting. Get the cruise to 13-13.5 and WOT as mentioned above (high 12-low 13)

The power valve may be hanging open. The PF carbs and most Holley's come with a 6.5PV and you have only 5 inches of vacuum at idle. If the best idle vacuum you can achieve is 5 hg then you need a 3.5 PV.

I'd also look at the base timing and try dialing in more. Keep advancing until you hit max vacuum and re-check to see what you've got. It may want a lot more initial than it currently has. If this ends up being the case you will have to go in and recurve the distributor.

Hopefully you've blocked off the vacuum advance because it certainly will not work with the low manifold vacuum that you currently have. 


Ron

[c00nhunterjoe]

Ron, my cam is a very similar grind and i only pull 7-8" @ idle. However, mine wont idle at 950, thats way too low for me. I also think it could use a little more initial. Mine is happy at 25/38 but i have alot less cubes and different heads.Another thing that i would ask is what oil do you run? Is there a possibility for cam wear in this situation?

[Charger_Dart]

Yes, I have the vacuum advance blocked off on the distributor. - I believe the power valve I installed is a 4.5, but maybe a 3.5 would be better?

More timing? How far would you go for initial?

I also thought about cam wear, but I don't have a clue how to check for that....... I have always run 20W-50 oil in the engine and it maintains high oil pressure hot or cold.

[firefighter3931]

If it's only making 5in at idle then the 4.5pv is still too big, inmo. Yes a 3.5pv would be better in this case. 

Before going through any of that...start by experimenting with the base timing. Advance it until the vacuum peaks and stop right there. Snug it down and get a reading. If you can restart the engine easily with no kickback....you've found your happy place 

My guess is that this engine is going to want lots more base timing and you should be able to double your idle vacuum....9-10 should be easily achievable with 500 cubes and the 509 cam. That being the case you won't need to swap out the power valve and it'll be just a matter of adjusting the mechanical advance and jetting changes.

Like Joe stated above....some engine combinations are not happy with a 950 rpm idle speed but yours should be able to run descent with that number or close to it. The big cubes soak up a lot of duration and mellow things down significantly.


Ron

[charger496]

   Do you run a zinc additive with every oil change? If not, and there's none in the oil you use, the cam could be wiped. Do you have a magnet on your drain plug? Cut open the oil filter to check for metal? Of course, timing and plug issues would be easier to fix, so fingers crossed...

[Charger_Dart]

Well isn't this something - I went out to adjust the timing like Ron had suggested and the engine would not fire. Pulled a spark plug wire and nothing.

I checked the MSD box and the ignition LED will not come on so I assume the box is toast since it has power to it. Maybe I have had a bad box these last 3 years and it gave up today?? I will replace it and see what happens.... 

Anyone know if the MSD 6A or AL boxes are any good?

[firefighter3931]

There could be nothing wrong with the box. The small red wire is the trigger feed....it needs a constant 12v to power up the box. Think of it as a switch 

The blue & brown wires coming from the firewall are engine start & engine run. These two wires have to be tied together and spliced into the small red. It could be that the start wire or ignition switch is bad.

Get a test light on these two wires. One will have a continuous 12V power supply with the key in the forward position. The other will have 12V in the cranking position only.

MSD boxes are usually very reliable....i've used several over the years and not had one fail.


Ron

[Kern Dog]

..... your idle vacuum....9-10 should be easily achievable with 500 cubes and the 509 cam. That being the case you won't need to swap out the power valve and it'll be just a matter of adjusting the mechanical advance and jetting changes.

My 493 with the '509 cam idled at 1100 in neutral with 10" of vacuum. The Lunati 316/326 gave me about the same numbers. I wonder if there is a vacuum leak causing the poor readings. What if the intake gaskets are compromised?

[Charger_Dart]

Update -

I tested the MSD box and just could not get it to fire. I found where I purchased it 2 1/2 years ago from Summit so it was long out of warranty. I packaged it up and sent it into MSD for repair , we will see what happens.

In the meantime, I hooked up a new MSD 6AL box and noticed 2 things in the instructions - They specify not to hook the 12V hot to the alternator post so I ran a new hot wire to the starter. They also recommend a 50 - 60 spark plug gap, so I pulled the plugs and re-gaped them to 55.

With no other changes the engine fired right off and had a much smoother idle.  The idle went from 950 to 1050 rpms. We had thunderstorms rolling in so I took it for a short drive and the engine really woke up! It runs so much better now and when I got back I pulled a plug and it was a nice tan color now, not black as it was before. I have not had a chance to take a idle vacuum reading or hookup my wideband, but it is running so much better now.

I guess I am lucky  that the box quit or I would have been wasting my time parts swapping & chasing other stuff instead of enjoying the car! 
   

[firefighter3931]

Thanks for the report...sounds like it's running good now 

MSD does not want the main power feed coming off the alternator. That is a recipe for trouble  I allways run the big red to the starter relay post and the big black goes directly to engine ground or the negative battery terminal.

Good to hear it's back up and running strong 


Ron

[Charger_Dart]

Thanks to Ron everyone else who contributed! Best board ever. 

[Charger_Dart]

Just thought I would post an update to how the engine is running -

I now have 7 inches of vacuum at idle - 1000 rpm

My AFR's got much better. I get the highest vacuum reading at idle with a 13.2 - cruise seems to now be at 13.4 and wide open seems lean at 14.0

Secondary jets are an 88 and I guess I need to go up to a 90 or more maybe?

Thanks!!

[firefighter3931]

Yep, 14.0 is lean at WOT  ....jet up to 90's and report back 


Ron

[1974dodgecharger]

yeah the purple 509 is a super low vacuum idle cam, lol.  My best I get out of mine is 6....

maybe your used to the power now?