Engine misfire

If the readings were that low on those old sleds then they were getting worn out. The older engines were generally lower than newer ones but still should be in the 175 range when good.
A general rule of thumb on compression is to figure 20 X the compression ratio at sea level. This will vary based on barometric pressure, engine wear, altitude, humidity, etc. but generally the number drops off a bit. What may be 190 at sea level may be 175 in Colorado Springs, etc.

You might pull the vacuum line from the fuel pressure regulator and see if there’s gasoline inside the hose. There should be none.

Still using those old sleds, the pickup is my fuel/ service truck off road, and the ford is on a c-6 automatic hooked to a 1950’s vintage 6 speed FWD trans and running gear; farm stuff in the north California valley. Thinking about trading the ford engine for older dodge cummins diesel and auto trans this winter, something without a computer or electronic smog to wire in. A lot of the older Oshcosh conversions are being changed over to 3208 cat with allisons but that is a lot of weight for the FWD frame.
Getting off track here, if I could pick your brain tomorrow about the s-10 after I check the pressure regulator out. Thanks

Is the timing off? That seems like it should be checked.

The timing chain may have slipped. Just another possibility. If it has, it is worn out and has to be replaced.

Won’t run to check timimg, and I think the book said it is not adjustable, all computer controlled

Could have, I’m not sure of the composition of the sprockets or chain. I know in the older 350’s the chain would wear through the cover and still not slip.

I’m still holding out on crank sensor/pigtail. There’s not much gonna make a starter kick back. I suppose the cam timing could be out, which in turn would throw off all other times. Get number one tdc and look at the rotor and see if it’s pointing where it’s supposed to. You’ll have to follow the trail on the cap. Fuel pressure regulator mounted in intake. You can r&r throttle body to look and see if it’s wet. Sorry, didn’t see there were more posts.

The cam timing looks good. My chilton book, which I’m beginning to hate, does a very poor job of showing the pressure regulator, in the CSEFI fuel meter body on the plenum I think. The pigtail to the sensor shows voltage, I replaced the sensor because the ohm reading was way below (56 ohms), chilton 800-1200 ohm, but the new one read the same as the old, I have this thing about returning electrical parts so I put it in. I should have noted that two of the cylinders had compression of 90 psi, #3 & 6. The old plugs all looked pretty much the same, not oil fouled, some carbon on the insulator but should have functioned. So now I’m wondering if both head gaskets could be at fault.

And…here is my new revised theory. The reluctor ring moved on the crank, threw the timing off, dislodged carbon in the cylinders and is preventing the valves from seating completely and since it won’t start the carbon won’t blow out. Sound feasable? I need a beer.

Sounds good to me. Would explain symptom of crank sensor failure.

Really? I was kind of expecting something along the line of “I’ve never heard of the reluctor ring moving on the crank, it can’t”, but I’ve never had one of these apart to know. If the engine ran smooth, no misses, no clouds of smoke, negligable oil loss, no oil in the radiator or water in the crank case, and rapidly goes to crap; I’m grasping for an explanation. So, off with the timing chain cover! or got any other ideas?
Wonder if the ohm readings on the new crank sensor being the same as the old one might indicate that the new one was faulty also. Need to know if that ring can spin on the crank first.

You probably need to halt right now. You state that 2 cylinders have compression readings of 90 PSI and this just flat sucks. Those are essentially dead weight being lugged along by the other 4, assuming the other 4 are good of course.

Run a wet compression test on those 2 low cylinders. Shoot a small dab of oil in one of the cyinders and retest the compression. If the reading takes a jump upwards (say from 90 to 120) then you have 2 possibilities.

  1. The cylinder walls are washed down with raw gasoline. This means the engine oil should smell like gas.
  2. The piston rings are shot; it’s engine work time.

Should I ask what the compression readings on the other cylinders are?

(I would add that what can happen with misfiring cylinders is that a spark that cannot jump the plug gap in a dead cylinder is going to attempt to go to ground somewhere. This means arcing through a wire to the head, jumping to another wire, jumping terminals inside a distrbutor cap, etc.)

OK, well it’s dark and raining so I’ve halted, tomorrow wet compression test. Can’t get the gauge in #3, the steering column is right in the way, work on an elbow for that…#1- 135, #2 140, #4- 180, #5 & 6 - 90. Thanks for the incite on compression, the new plugs I put in were wet with fuel after trying to start it. So if the wet test is negative how does my carbon theory sound?

What you need to do is follow the flow chart in the manual. What you are doing now is jumping all over the place, you do not have a stratagey. Having a diagnotic stratagey is important for diagnosing anything. At GM they gave it a name “Stratagey Based Diagnostics” I am sure that in other technical areas there is a coresponding name.

I’m a farmer, we never do anything right the first time or the second for that matter. I forgot about something else, the boy said the tow truck driver was trying to get it to run and that it kept backfiring and sputtering before he gave up and towed it back, so I think I might have two things going on; the cause and the damage done. Oh well…

Well, you got problems pretty much across the board. There’s only 1 cylinder in the batch that is half decent and that’s the 180. Everything else sucks or is attempting to suck.

Odds are if you perform the wet test on the 135 and 140 cylinders the reading will take a jump up on those also.

Ring problems (omitting the worn out due to high miles scenario) are usually caused by oil coking/sludging due to irregular oil changes seizing the wiper rings or rings damaged due to an overheating engine.
Overheating can coke oil, gald cylinder walls and pistons, and remove the temper from rings, with temper being the springiness so to speak.

Honestly, I think the engine is toast due a ring problem and the carbon scenario is not valid. Just my opinion anyway.

Well thanks, usually what I do with a problem like this is tear the whole thing apart, if I can’t find anything, put it back together and see if it works, then go get another motor.

Doesn’t that motor have the spider injector system? Also fuel pressure regulator is attached to that system.

Is it hard to start? Blows out dark smoke when it finally start? That indicates fuel pressure regulator/ spider injector system.

Also , is the check engine light on? Does it read coolant temp sensor?

Also, alot of new distributor caps are defective. How did the installation of the sparkplug behind the steering shaft go?

Hm, lots of questions. yes spider injector system, cap and rotor about 6 mos. old and ran good, engine kicked back to bad to run long, now won’t start, no codes shown or stored. Ah the plug, stuck a piece of fuel line on the end to get it seated then the swivel socket would fit. Fuel pressure regulator is on my list of things to investigate

Computer controlled…see if you can have a shop do a substitution test. If it works with the new computer, the old one is giving bad timing orders.