Idle rises when I pull plug wires?

Tiny
PUNADOG
  • MEMBER
  • FORD F-150
I just put a '94 302 longblock into my '84 Ford F150. Used the '84 distributor and intake and carb. "94 engine has 118,000 miles on it.

I have a miss that I couldn't track down so I bought a good multimeter that has a tachometer. Pulled each spark plug wire and noted the difference in RPM.

Base RPM was 460. Four of the cylinders had RPM drop to 410-420 indicating working cylinders. The other four had the RPM rise to 520 when the spark plug wire was pulled. What does that mean? To add to the mystery, it runs in pairs in the firing order. 2 have rpms drop, followed by 2 where rpms will rise. Not sure where to go from here? Warped distributor?

For sure the wires are on the right plugs. New plugs, wires, dist cap and rotor. Timing set at 10 degrees BTDC.


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Wednesday, October 31st, 2007 AT 1:16 PM

6 Replies

Tiny
RASMATAZ
  • MEMBER
Very strange, is it wired like this below


http://www.2carpros.com/forum/automotive_pictures/12900_Firing_order_302_1.jpg

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Wednesday, October 31st, 2007 AT 3:19 PM
Tiny
PUNADOG
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I've been using the firing order 1-5-4-2-6-3-7-8. This is the firing order from the '84 and is the firing order of the '94 in all of the literature that I could find. I've never seen the 1-3-7-2-6-5-4-8 anywhere. I'm going out to the garage now and will let you know the results. Where did you come up with this firing order?
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Wednesday, October 31st, 2007 AT 5:51 PM
Tiny
RASMATAZ
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You sure your engine is not a 351W. FIRING ORDER 1-5-4-2-6-3-7-8 DISTRIBUTOR ROTATES COUNTERCLOCKWISE
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Thursday, November 1st, 2007 AT 12:45 AM
Tiny
PUNADOG
  • MEMBER
This just gets more strange. I thought you nailed it with the modified firing order. Truck starts right up, engine revs great in neutral. Tried test drive and the engine bogs down when you give it gas, almost to the point where it dies, then it slowly will start rising in rpms, but is seriously lacking in power.

So today I finally tried the test pulling the plug wires. Base rpm is 570-580. Now all cylinders rise when I pull plug wire. Some more than others: 1-600 rpm, 3-600 rpm, 7-600 rpm, 2-630 rpm, 6-600 rpm, 5-600 rpm, 4-620 rpm, 8-630 rpm. Firing order 1-3-7-2-6-5-4-8 with distributor running counterclockwise.

For sure this a 5.0L 1994 engine. Are there any other firing orders out there? I can't believe this thing even runs. In fact, it runs great in neutral.

I've really appreciated your help, and I will be sending in my donation if/when I get this thing running right. So far it has been a bottomless money pit.

Thanks again for your help.
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Monday, November 5th, 2007 AT 5:24 PM
Tiny
INDYUKE
  • MEMBER
Firing order is dependant on the type of cam you have. All 351W and '94 and later 302's have the 1-3-7-2-6-5-4-8 firing order. Pre 1994 302's have the 1-5-4-2-6-3-7-8 firing order. If you use the wrong firing order, the engine will run, but just not with any power. I've pulled my hair out over this one when I first came across this issue.

When you tried the 1-3-7-2-6-5-4-8 firing order, did you time the engine and make sure the advance was hooked up?
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Friday, November 9th, 2007 AT 7:32 PM
Tiny
IMNOTLOKIN
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1-3-7-2-6-5-4-8 is correct for the 94 5.0. I have the same thing and the same problem. I advanced the timing to much and lost all power on the road. After turing it back counter-clockwise to 10 deg. It runs like a champ.
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Wednesday, November 14th, 2007 AT 5:13 PM

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