1981 ford f-350 300 in line 6. Bolt holding main pulley to camshaft fell out. Saw alternator light come and thought it had gone bad and was running on battery so I rushed back to my garage not noticeing the heat guage. When parked radiator was boiling, extremely hot. Replaced bolt, new coolant oil and belts. Engine seemed to have a miss at idle but once moving ran fine but was running a little hot . Yesterday it stated bucking and jumping, then started to backfire. Did checks for blown head gasket. No coolant in oil, no drop in collant, no blue smoke at tail pipe. Have not done compression check yet. I did pull #1 plug and cranked engine so distributor rotor was pointed at #1. Piston is at bottom of compression stroke ? Engine starts and runs. Can rev engine and no miss. Once in gear backfires and bucks. Where do I start. Appreciate any help.

 

Go ahead and do your compression check.

 

Did compression check:
#1 65
#2 120
#3 90
#4 120
#5 120
#6 120
Could #1 be the head gasket or ??

 

Or valves not seating, or broken rings, or cracked head or block, or......

They should all be within 10% of each other, there are obvious problems there (assuming
those test results are valid).

 

Guess I will put some air in there and try to find out were it's coming out from.

 

Had to park truck for awhile and just got back to it. Did compression test again, re your comment "if it was done right", following manual carefully. Apparently not done right. Lowest reading 105, highest 110. Then did leak down test. Hishest leakage was 10 percent. New plugs, wires and distributor cap. I still have a problem with 1 & 2 cylinders. Compression on these 2 was 105 and the rest at 110. I can pull plug wires, at idle, and the engine runs the same. Engine lacks power.

 

Can anyone give me some input?

 

colappsed lifter maybe form over heating?

 

I'm thinking the previous overheating and current running problems could be unrelated,
they occurred next to each other by coincidence. Hope so, anyway.

It seems to run fine until you put it in gear? I've seen that here before but can't remember
the specifics.

BTW I'm assuming an auto transmission, correct?

Also, please click on User CP in the top-left and finish filling out your profile so we can
see where you're at.

Back to the engine.... The compression & leakdown tests look OK to me - the engine is
a bit worn and is definitely not a Spring Chicken but should work.

If it were a collapsed lifter or stuck valve or whatever, I would think you'd detect
something odd in the movement of the needle on the compression gauge when you did
your tests, those two cylinders would behave differently on the gauge than the other four.
That's not the case, is it?

My first suspicion is gonna be electrical and ignition-related, as in some wires get
shorted or disconnected when moving the shifter lever.

Do you have a volt meter? What voltages do you get at the coil while in Park and then in
Drive?

But, that's not going to explain pulling the #1 & #2 wires and not making a difference...

Swap the #1 and, say, #6 (or anything other than #2) wires and start it up, pull the #1
wire, is the behavior the same? Plug it back in and then pull the #6 (or wherever you
swapped it with) and see what the behavior is - does the problem follow along or stay
behind?

 

Yes it is auto xmsm. I do have a miss at idle, just more noticible put in gear. I have tried switching wires around without change. Installed new set of wires without change. Checked each cylinder with compression guage while running,#1-70, #2-70, 3-6 were at 90. Using vacuum guage I can only get 13 inches with a tick in the needle.

 

Did you replace the spark plugs? Excessive heat can damage or crack the insulators causing them to not function properly. Plugs are cheap.

Did the affected cylinders leak compression at all? Go up to 105 and start to drop after a little? etc...

Also did you remove ALL the spark plugs during the compression check?

A Head gasket on a 300-6 can blow in one of three ways.

1: Water to Oil: Symptom Milky engine oil.
2: Water to Combustion chamber: Symptom, steam coming out exaust.
3: Cylinder to Cylinder: Symptom, two adjoining dead cylinders. A Compression check will only diagnose this if ALL the plugs are removed as it will still seal between them with the plugs in.

It could be a bad head gasket between combustion chambers. Perhaps between #1 and #2. with your previous tests. Redo the compression check with all the plugs removed if you didn't before.

It only has symptoms when in gear? It runs perfect with it in park or neutral. Could be the vacuum modulator for the tranny, however the engine would smoke from it sucking tranny fluid, so I doubt this is the cause.

It could be the load on the engine with it in gear. Bad valve return springs due to heat damage, valves or hydraulic lifters collapsing under engine load. Check and change the engine oil as well.

After changing the plugs and oil, if it still does it, and you can't get anywhere farther with the compression check, you will need to remove the valve cover. Then run the engine briefly, with it under load, it will be a little messy but you will be able to see which valve is sticking or malfunctioning and where.

 

No longer have backfire, new distributor, but I don't know if that was a cure. Tried to set timing with vac guage and could get only 13 inches at best idle, full range of adjustment with distributor but only 15-20 degrees before engine would start to stumble. New plugs, new plug wires,new oil, changed antifreeze and thermostat. I did compression check with plugs out and noticed no leak down in compression. Did compression twice on all cylinders and checked each twice both times. No water in oil, no water at tail pipe. Have checked for vacuum leaks and have found all tubing hooked up. Sprayed starter fluid around around intake with no uptick in rpm. Engine misses at idle, miss is accentuated when in gear while holding brake.. I replaced plugs and plug wires before I did compression check. When I pulled the plugs for compression check, they had been run for about 50 miles, plugs in #1 & #2 did not have combustion burn like the other four. Checked spark on both, bright and blue. Had valve cover off and all valves more freeley. When plugs were out used light into plug hole,could see valves moving while turning engine with remote. Did not check valve function while in gear if that's what you mean by under load. I appreciate your help. This is frustrating!!!

 

Yes that is what I meant by under load. The valve springs may be strong enough out of gear but put the engine under load (In Gear), and they might be collapsing on you.

A vacuum gauge may not be the best way to time this engine. The best way would be to use a timing light and the emissions label on the radiator support. It should be timed either at 6 degrees or 10 degrees BTDC.

 

Normally, I would agree with you, but this guy lives in Colorado (as do I) and he's got
high altitude and low-octane gasoline to adjust for.

gordo: Is the truck native to Colorado? Or did it migrate from sea level?

I'm in the Denver metro area, down around 5300'; I seem to recall reading to advance
the timing one or two degrees for every 1,000 feet in elevation but it's been a LONG
time saw that, I could be mistaken.

In any event, my timing is around 14 BTDC and I re-jetted the aftermarket carb, down
I think one size as two sizes seemed to burn a bit lean ( as determined by the color of
the spark plugs after 1,000 miles). Holley recommends going down one size for every
2,000 feet in elevation.

If the guy lives up at 9 or 10,000 feet, different adjustments will need to be made.

My vacuum gauge shows 16-17 in normal operation at a warm idle.

I should also mention I have a 400 V8.

The gasoline octane readings here for pump gas are generally 85, 87 & 91.

I could probably retard my timing and use 85, I use 87 right now and seem to do ok (no
pinging under load) but my engine has been rebuilt and is pretty far from factory.

Do a google search on this and you'll find a lot; here's a link to some stuff, it appears
to be authoritative on first glance but I didn't read it, just skimmed through it. It's
directed at Saab owners but that's OK.

Another link to a Holley PDF on performance-tuning techniques.

For gordo, I would suggest starting at 12 or 13 BTDC if he's down in the lower
elevations, I would say up to 15 BTDC if he's up at 9 or 10,000 feet.

The best way to adjust the carb IMHO is with an exhaust gas sniffer, this is one area
in which I think modern EFI just rocks.

Altitude Adjustment
www.holley.com/data/Products/Technical/R7849-2.pdf

 

Actually this truck was made in Canada and first registered in California, however, thie engine is a rebuilt as well. Installed in Ft Collins. Engine has probably 20,000 or so miles and ran fine, little hard on gas, but ran okay until it overheated. The engine has no timing marks, the installer apparently left it off when installing the timing cover. I think it is a bolt on item like the timing cover. With no reference point for timing it makes it more difficult. As I posted earlier I have full range of adjustment in the distributor but only 15-20% of that adjustment before it stumbles. From the condition of the plugs it appears I am not getting combustion in 1 & 2 cylinders. Spark, fuel and compression for combustion right? Weak coil?Wouldn't that affect all cylinders not just two? Distributor off a tooth and messing up timing? Looks like I will have to go back and check two problems cylinders again, compression and leak down tests. I think I'am down to lifters, valve springs, or blown gasket between these two cylinders. Last thing I want to do is to pull the head. Appreciate your help.