Crank position sensor

[Mike McKown]

I think that's what it's called. In the distributor. Senses crank/distributor position.

If it is faulty, what running abnormalities will I see in the engine. Spark knock? I'm getting an occasional hard spark knock for no apparent reason under slight load. Then, just as quickly, the spark knock goes away. It will even do it using premium gas but not as bad. I haven't checked initial timing yet only because I don't think that's the problem. The problem is intermittent. How would I check it for function?

The fuel mileage is around low/mid 30's which to me is unacceptable even if it is an automatic. That's featherfooting the gas pedal, mixed urban and highway.

Other than that, runs good.

[FB71]

CKP (CranK Position sensor) has no influence on spark knock. It is used primarily to determine RPM and provide that data to the ECM (computer) The ECM determines spark timing based on RPM, throttle position and altitude. Barometric pressure sensor (BP) is located inside the ECM, and is not serviceable.

If the CKP were to fail, even intermittently, the vehicle would stall or stutter severely.

[Mike McKown]

[QUOTE=FB71;168631]CKP (CranK Position sensor) has no influence on spark knock. It is used primarily to determine RPM and provide that data to the ECM (computer) The ECM determines spark timing based on RPM, throttle position and altitude.



As it (CPS) senses RPM, that's why I thought it might have something to do timing.

I have two other parts cars I can get an ECM out of to check against. Would you suggest I adjust or check the TPS for the cause, ECM or look elsewhere?

I have a factory manual but it only describes functions of inputs/outputs of engine electronic control components. Not troubleshooting. Is this contained in the Festiva Electrical/Vac service book?

[FB71]

No, EVTM only has schematics/diagrams. You need a Powertrain Controls and Emissions Diagnostic manual (PC/ED) for diagnostic proceedures.

The TPS is a 3-state switch, not a potentiometer like more modern vehicles. It has an idle validation switch cicuit and a WOT (Wide Open Throttle) validation switch circuit. Between those two states is a dead zone. I don't recall which wires are which, but one is a ground wire, one is Idle Signal and the other WOT signal. The sensor just shorts the signal wires to ground in the appropiate state.

BP cannot be tested without speciallized equipment and electronics knowledge, so a swap with a KGP (Known Good Part, yes, this is an actual Ford acronym) is the only real test you can do.

Now, Here's what I think you might want to check. Install a fuel pressure test gauge and go for a drive. Watch your fuel pressure during these spark knock events. General rule of thumb is "lean is mean", meaning, a slight lean condition can increase specific cylinder pressures slightly, yielding a touch more power, but leaves the cylinder prone to spark knock. I suspect you may have fluctuating fuel pressure, possibly due to a weakening fuel pump. During WOT, the ECM fully retards timing and goes to full enrichment (open loop), so spark knock isn't very likely. During idle, spark advance is moderate, and there is little load on the engine. Part throttle, with slight tip-in (to compensate for small changes in load, inclines, etc)in a higher gear, can place a huge amount of strain on the engine. The ECM is relying on RPM changes and Baro readings to pick an advance point, but this is only a best guess picked from a lookup table. These older systems rely on the engine itself being knock resistant.

The other possible contributing factor may be carbon buildup in the combustion chamber from slight oil consumption. Run a can Seafoam (or similar product) thru the intake to remove the carbon, and see if that helps.

[Mike McKown]

Okay, I understand everything you're saying.

Your comment about lean fuel is interesting. I've often wondered if that is related to an overly long crank time on a cold start after sitting overnight? I've wondered if the fuel pressure was low or bleeding off the fuel rail sitting overnight?

Carbon? Could be. Every once in awhile, it'll smoke out the exhaust under load, then it'll quit. I'd say the engine isn't real tight but it's not worn out by any stretch.

The spark knock occurrs at part throttle. Can't say about wide open throttle as I tend to start pulling back on the throttle when I hear it rattling. This is no small event. It's pretty severe.

I'll try what you suggested and get back with the results. Thanks.

I think I need to find the manual you spoke of too.

[FB71]

yes, the long crank issue is definately related.

Next time the knock occurs, stab the pedal to the floor. This will force the ECM into open loop, dump lots of fuel (cooling the chamber) and retard the timing. It should go away under those conditions, if it's only carbon. If it's low fuel pressure, it won't go away easily.

[Mike McKown]

I copy. If I get time, I'm going to rig up an in-car fuel pressure guage today.

Giving it a little more thought, I think the car only does this after it's run awhile, going up a hill or the gasoline level is low in the tank. Everything you're saying makes sense. It could be something as simple as a clogged sock on the fuel pickup.

I'll be back.

[Mike McKown]

I thought I'd follow up.

I put a fuel pressure guage on the engine and drove around for a couple days. 28-38 lbs. depending on engine load (vacuum). About 85 lbs. with the return line squeezed off. It's not the pump, filter or regulator causing the problem with the spark knock.

Something is causing the problem with long crank time here though as the fuel pressure starts dropping as soon as the engine is shut off. It'll restart after sitting all night as soon as the pressure pumps up from zero to 30 lbs. Does the fuel pump have a check valve in it to stop bleed back? The regulator should have. How do I determine where the pressure bleed is?

I may have found the spark knock problem. When I removed the air intake, there was a lot of oil standing in the intake pipe which tells me blowby is getting in there. That also explains why I'd see it trail smoke every once in awhile but not always. Anyway, the PCV valve was stuck. I cleaned the pipe out and went down the road. No smoke. Light spark rattle, nothing like before. I think there is some carbon in the combustion chamber and I'll get to that next.

I also took a look at the EGO sensor because of what was in the intake. It was muddied up. I put a new one in. I hope that explains the 32-33 mpg I've been getting. I think I should get 40 or better. We'll see.

Thanks for the help so far.

[FB71]

check valve is part of the pump assembly. Fuel pressure should not leak down more than 10psi within 2 hours. That's definatgely the source of the long crank issue. Stuck PCV sending oil into the intake will definately cause spark knock. Run a can of Seafoam thru the intake. Or use Jim's Special Sauce... 3qts hot water, 1qt trans fluid, shake into pink milkshake. Have engine at operating temp, feed mixture into intake thru canister purge line, while keeping rpms around 2k. Do not allow to stall. If the engine bogs heavily, pinch off the fluid line till the engine recovers. It'll smoke like a freight train, but it does a wonderful job of steam cleaning the combustion chambers.

Replacing the EGO was the correct action, it was almost definately oil fouled.

Lastly, check your ignition timing, just to be sure.

[Mike McKown]

[QUOTE=FB71; Have engine at operating temp, feed mixture into intake thru canister purge line, while keeping rpms around 2k. Do not allow to stall. If the engine bogs heavily, pinch off the fluid line till the engine recovers. It'll smoke like a freight train, but it does a wonderful job of steam cleaning the combustion chambers.



I always just used plain water to steam clean the combustion chambers. I haven't had to do this since leaded gas went away and that's been what, 35 years ago. I suppose the transmission fluid wouldn't hurt anything.

[FB71]

the trans fluid helps keep the intake valve stems lubed, and prevents wash-down of the cylinder walls.

[Mike McKown]

I used the hose to suck about 5 ounces of water through the intake. The spark knock is gone. Thanks.

I'll know in a few days if the EGO sensor took care of the milage.