Engine Won't Start (HARD ONE!)

1991 Ford Explorer 3.0 V6

After I replaced the head gaskets on this vehicle, it would not start. The battery/alternator are good and the starter motor turns the engine over at a quick pace, with the moving drive belts and obvious turning-over sound confirming this. But the damn thing will not start.

This vehicle is equipped with a Ford electronic distributor. I checked for spark at the spark plugs, and that was good. Checked for fuel to the cylinders from the EFI system by turning the engine over with no plugs. Plenty of vaporized gas built up on the spark plug hole threads. Even caused a small fire at one point cheking for spark/fuel. The Air Mass sensor has a good connection as well.

What could be causing this engine not to start? The thing I'd like to know is how does Ford's electronic distributor KNOW which turn of the camshaft the crankshaft is on? There's a crank angle sensor right at the crankshaft pulley, as on many Ford vehicles, but how would the computer know which turn the camshaft is on?

The reason I ask this is because the engine sounded like it backfired on two occassions, suggesting bad ignition timing. I did NOT have to touch the timing chain when replacing the heads, thankfully, so valve timing is the same since before I touched the car.

What about compression, also? I did a compression test and the results had a kind of big gap. The lowest cylinder was 105 PSI and the highest cylinder was 180 PSI. This might cause problems later, but would it cause the engine to not start at ALL?

Do you have the wires in the right order?

soounds like your distributor is 180 degrees out... mark where it is now and pull it out, set exactly 180 degrees opposite and reinstall

Sounds like the timing is off. Make sure the distributor is in the right place. I would get a service manual for the vehicle. It will tell you how to set up the timing.

Sorry I was kind of vague when trying to describe the distributor initially. The Ford Explorer I worked on has a DIS (Distributorless Ignition System). You've seen one of these? The distributor looks like the bottom picture in this image:

http://z.about.com/d/autorepair/1/0/L/Q/figure4.gif

It's all electronic distribution of the spark. The extra element is a crankshaft angle sensor right at the crankshaft pulley cog, which is marked with notches to reflect the laser pickup. There is no gear pinion on this distributor going down into a gear on the camshaft.

Which is why I asked all that stuff about the camshaft, which you would THINK would need to be monitored with a separate device if not gear-and-pinion timed. I found none during the repair, and the Haynes manual says nothing about a camshaft sensor for the DIS system.

It sure does sound like the timing is off though...it might be that I replaced the spark plugs in the wrong place, but I'm pretty sure its right. The Haynes manual doesn't show which goes to which though,which makes me wonder if I put them back on wrong. The distributor points down the engine in the same formation that the cylinders take, and I believe that each cylinder goes to each corresponding spark plug receiver on the electronic distributor box thing. I might be wrong though.

If you could check a Ford shop manual that would be awesome! Thanks.

If the cam sensor is mounted inside a stubby "distributor", then the engine will start and run in the sensor is in the wrong position. It may not be as smooth as if it were correct, but it would run. There isa special tool for this installation, and it needs to be used. NOW, to the real subject. If your compression is 105 to 180, then you have an issue to deal with here. I am assuming that you had the valves done when the heads were off, and that they were fluxed and planed, insuring a good set of heads. What is the reason for the head job in the first place? What was the compression prior to the head job, how many miles on the engine, are there any codes stored, are all the sensors plugged in, and are the grounds all grounded? Re-post please with more information.

It probably does not have a cam sensor, it just assumes that the motor is timed right. Like said above, your compression results are fucked up, but it should fire still. I would ask for the firing order in the ford forum, I'm sure someone knows. Most of the time the order is not reflected onto the distributor from the cylinders (also check the owners manual if you have it, it usually has firing order).

first off. its a 4.0L OHV. The explorer was never offered with a 3.0L

If it ran before you did the headgasket, I would suspect the work before I'd suspect something completely unrelated failing. Either you completely fubar'd something or the motor is junk....take your pick

Oh yea you're right. It is a 4.0 *smacks head* I've been working on too many cars since I did that one.

The reason this vehicle's head gaskets got replaced is because it overheated really bad and at least one head gasket blew on it. When I took the heads off there was a ton of water in half of the cylinders. The guy ran the vehicle in this condition until it would not start anymore. I never saw the damn thing running

Yea its good to get a confirm on the shitty compression numbers. No we didn't do the valve seats. Gotta take them off again and do a garden hose test on the valves, see if any have a major leak and try to fix the ones that do. I suspect not enough torque on the head bolts (80 ftlb instead of 180 ftlb) may be partly to blame for the bad compression numbers. I'm not sure the guy wants to invest 400 or 500 bucks in redoing the heads. He only wants it to run, not have a rebuilt engine.

As for the ignition timing questions, I don't think he has the owners manual. He is not the original owner. And the Haynes manual doesn't have it (the order of spark plug wires for the digital distributor box thing) , at least not from what I'm seeing.

And about the camshaft, I'm still not getting how the computer knows which rotation the crankshaft is on. Do you have to disconnect the power to reset the thing, then set the crankshaft on the correct stroke in relation to the camshaft? Understanding the mechanism would be helpful. Thank you for the pointers so far! I think we can salvage this car after all.

Haven't checked for codes yet. I still need to get an analog voltmeter. Damn Harbor Freight doesn't sell the things. Guess I'll be shelling out to Autozone for one. Too poor for a real code reader. Will get back to you on that for sure.

All electrical connections are connected, and all grounds are grounded. I checked all that stuff half a dozen times, especially the air mass sensor (big duh). The fuel delivery system is working and there is spark to the cylinders, I confirmed this. But the timing must somehow be off...either because I stupidly mixed up which spark plug wire goes to which terminal on the digital distributor, or because computer can't tell position of camshaft from the position of the crankshaft.

if you don't know which wires go where on the coil pack, that could definitely be a large part of your problem!

On the left side of the motor, the wires go to the corrilating coil plug. 1-2-3 front to back. The right side (driver side) is not the same though, it goes 5-6-4 front to back. The numbers are usually stamped on the coil pack, but not always.

There is no "distributor" hole, sensor or any cam sensor period. This is a wasted spark system. The computer doesn't need to know which phase the cam is in, because its firing both corresponding cylinders at the same time, but one will be on compression stroke and the other will be on the exhaust stroke. Everything is calculated from the crank sensor.

actually, with the older exploders, I think the coil pack was turned sideways. If thats the case, the rear 3 holes of the coil pack, left to right (passenger side to driver side) is 123. Front row is 564.

Uncle bob you are the MAN! Damn, thats all I needed to know right there. So I did mix up some spark plug wires, and I don't have to worry about the camshaft. Cool! Thanks again buddy.