Hello everyone, I'm posting this today to see if anyone can help me. I've just recently purchased a 1985 Bronco with the 351W. When I first bought the truck it ran horribly. The first thing I did was rebuild the carb. because I noticed that the choke wasn't working at all and the secondary wasn't kicking in. Now the carb works like a charm. I've set the idle, set the timing, replaced the plugs, replaced the distributer cap and rotor switch. I've noticed that when I pull the wires off of the distributor cap one at a time that there are two that do not affect the motor when it is idleing. I verified that there was a spark on both plugs. I can also pull the plugs and see that they are all burning. My compression is approximatly 125 on all 8 cylinders. The exhaust seems a little rich to me also. I verified the wires were all going to the correct cylinder and I have checked to make sure that the wires were properly secured to the plugs several times. I havn't checked to see what my timing advances to once the vacuum line is plugged in but I'm not sure what it should be. Any help would be greatly appreciated.

Thanks,
Chris Waldrop

 

If you know you have spark at all the plugs, has good compression, you've set the timing and rebuilt the carb with sucess. Whats the problem?

IMO, if the distributor was set up from the factory / original to the vehicle and it runs right, I'd leave it alone. I'd check that the vac advance is working, connect direct manifold vacuum to the vacuum advance and start the truck, it should idle at a higher rpm than normal. If it does reconnect the vac hose to its original vac port and leave it. Otherwise you might get lost in trying to tune it for an extra hp or two thats not there. Good luck though with whatever decide to do

 

The Vacuum port from the carb is connected directly to the advance on the distributor. That is the way the schematic under the hood shows it. Most of the vacuum lines are missing or plugged off. I'm going to start working on that. I also know that my EGR isn't hooked up either. It is there but there is no vacuum line going to it.

When I pull the plug wires shouldn't I notice a difference in the way the engine idles? Shouldn't it idle a little rougher? There are two wires I can pull and the engine makes no difference to the way it idles. The engine idles rough all the time. If I have two plugs that aren't fireing at the correct time wouldn't this cause me to lose more than just a hourse or two?

 

Not necassarily.

They'e playing around with newer cars, in which the computer shuts down power to certain cylinders so that the vehicle gets better mpg when cruising.


Did you take the distributor out? Are you sure its not 180 degrees out?

A vacuum leak would cause your truck to run poorly as well. Make sure all the vacuum ports are sealed shut and the vac hoses are good.

Might wanna double check your firing order as well.

There are many reasons why your truck won't idle well.

Is this truck still using the stock camshaft?

 

Well I can't answer that. I have no way of knowing without pulling the cam out. I also personally haven't had the distributor out but that dosen't mean that it hasn't been out. How can I check either of those. I checked the firing order once before but I will check it again. I've also noticed that the vacuum diagram under the hood dosen't match any of the diagrams that claim to be for may year truck. Not even the ones in Chilton's. I've been going by the one under the hood. I'm going to re check my mixture setting also. I was wondering if a worn cam could cause this to happen. Is there some way that the exhaust valve could be opening before the spark plug fires? Or perhaps the plug isn't fireing at the correct time. I don't know what would cause that other than the distributor. I would think that a bad cam would show up on the compression test?

 

Hard to say as I don't know what you call rough idle. Your firing order being incorrect would be one reason. Are you sure its a 351w firing order goes counter clockwise on the distributor cap 13726548 the cylinders are numbered facing the engine, closest to radiator back, passenger side 1 - 4, drivers side 5 - 8.

Take number one spark plug out, rotate the crank clockwise with your finger over the spark plug hole and when you feel air blow past your finger, bring the damper to where the pointer is pointing at 6 BTDC, make a mark on the distributor cap base that is inline with the number one cylinder terminal, take the cap off, the rotor should be pointing at the mark you made.

 

The rotor was pointing at the terminal opposite of the #1 Cylinder Terminal.

 

Sounds like that is your problem your 180 degrees off. Lemme know what you find out. Easiest thing to do is take the distributor out and stick it back in with the rotor pointing at the number one terminal mark. They can be tricky to get back in, so don't be concerned if it takes a couple tries. Good luck

 

I'm going to give that a try. However I have a few questions. Would I get other symptoms besides just a rough idle? I don't know all there is about the duraspark ignition but it boggles my mind to think that the engine will run 180 out. Wouldn't I hear a lot of pinging and backfiring? The engine idles a little rough and it smoothes out around 1000rpm. I can also hear a little miss when I accelerate before the engine has warmed up good.

 

Your positive you brought the number one cylinder to top dead center. Facing the front of the truck, left side closest to the battery, the cylinder closest to the fan/ front of the block?

Just be 100% sure its 180 out, then correct it as mentioned and go from there, chances are a couple of your other symptoms will go away.

You'll have to play with the idle mixtures screws and adjust idle rpm but thats no big deal.

 

Just to let you know I went out to my truck on my lunch break and verified that the #1 cylinder (the one closest to the fan on the left side of the engine near the battery) was at the top of it's stroke and the rotor was facing the #6 Terminal (at least that is the terminal that the #6 wire is on). I had someone put a screwdriver into the spark plug port and feel the piston go to top. In this position the dampner was showing 6 BTDC. I'll let you know how it turns out when I rotate the distributor but before I do I wanted to know if I would Get the same affect by relocating all of the plug wires on the Dist. Cap?

Let me know what you think.

 

Why not? If they will reach....there is no reason for a particular orientation of the distributor or wires. I would say your gonna have to adjust your idle speed as well. Does the truck feel like it has no power? When the person stuck the screwdriver in the hole, did they feel for air to blow past their finger first? This determines the compression stroke and to find tdc on number one, it has to be done on the compression stroke, if they didn't then the procedure you have done may be inaccurate. Good luck

 

I did the test one more time and found that on the compression stroke the # one cylinder is being fired (the rotor faces that terminal on the dist. cap). I had someone hold there finger over the hole while I turned the crank until it built up pressure, then set the damper to 6 BTDC. .I can't reach the plug hole and turn the crank myself because the truck has a 3" body lift which makes it hard to reach down in the motor and do a whole lot. Could my pick up coil be causing this? The spark on the two cylinders that are in question dosen't seem as fat as the rest of the sparks that are going to the other cylinders. I think I'm going to change the plug wires even though they test good with an OHM meter. Approx 5.72 K. The truck dosen't seem like it has lost all power but it doesn't feel like it's all there. I find myself really having to lay onto the accelerator sometimes. I also think that it should spin the tires but it dosen't. I notice it dosen't like to climb hills either and the exhaust smells rich. I don't think that it is the fuel mixture.

 

do you have a vacuum gauge?

Would be a good idea to connect a vacuum gauge to the manifold and adjust the idle mixture screw(s) slowly, until the gauge reaches the highest vac reading it can make, when it stops building up vac, stop.

My opinion, if you have spark at the spark plug and the timing is set, your problem is somewhere else. I wouldn't worry about the plug wires or distributor right now. On second thought, if you were to have a bad wire and it had a crack and was arcing a spark against the block then it would appear to have a miss sound. When its dark out, start the truck and let it idle, pop the hood, make sure the underhood light isn't on, and look at the plug wires, if there is a crack in the wires you will see a spark. I would guess your problem lies in the carb if the wires check out to be good. Man, I was hoping it was the timing....good luck, later

 

Another thought, my 87 351w had good compression and ran great with high miles, it was a 2wd and it would not break the tires loose. I have the posi 3.55 rear with a c6. I changed the timing from timed vacuum to full and tweaked this and that, it'll break them loose now.