Thanks. That's what I set it to but this is not going well. With my nice new gaskets and clean top end the motor looks much better and is sealed up nice, but it runs like crap. I set the timing to 10 BTC and it runs poorly on gas and not at all on propane now (backfires on propane which is something I have not seen before) Noticed a 'notch' in the crankshaft damper with some red chalk in it far, far away from the proper timing mark so I have a great fear that someone did something dramatically different to the computer on this truck when the propane was put in. It will be crawling to the shop here in town that specializes in propane setups. I will be actively looking for a motor from around '86 and pursuing carburetion and standard ignition. This EFI and EEC stuff is for the birds.

 

I don't know, but on my straight six, it had to timing pointers. one on the drivers side, and one on the passenger side. the one on the passenger side is the correct one.. don't know if the 302 has that setup or not.

 

I disconnected all the electrical connectors, checked all the wires including the ignition wires, reconnected everything, removed the ground clip on the SPOUT, reset the timing, ran the truck for 10 minutes and now everything runs very smoothly.

Obviously something was not connected properly but I don't know what. I'll blame the mechanic (me) instead of the tools
I read that when resetting the base timing you have to give the engine 10 minutes or so of running time to reset itself, although I don't know why.

Anyhow, here is the result. It is set at 10 BTC. Starts and runs much better on gas than it did before, but once fully warm it will still stall when coming back down to idle at low speed. Pings only a little bit now under load. A mechanic friend suggests that the engine has worn itself into settings slightly different than original factory defaults, probably because it has run more than 90 percent of the time on propane. Runs fine on propane but is a bit of a dog going up hills, probably because the timing is no longer advanced as much as it used to be.

I'm going to drive it like this for a while. Still don't know whether its better to replace this engine when it gets old (not far off) with a rebuilt carbed model and drop propane altogether. Hmmm, maybe a 351 or 460? Can you get good HP out of a tricked out 351, is it better to go 351W, 351M or 351C, or do I just go for size? Rebuilt a 460 in my Lincoln with an RV cam and 850 cfm carb and man did it go... so much that I needed to buy a gas station.

Thanks for all your help folks. This is a great forum.

 

Glad it's running a little better.
The easiest motor swap would be to a 351W. They can make alot of power and not too bad on gas.

 

and I appreciate all your information. Hope I can somehow return the favour someday.

Is there a preferred model year for the 351W (remembering that I want to go carburetor) and would it basically bolt in where the 302 is or would there need to be motor mount and bell housing adjustments?

 

you probably want an 84 to 87 HO. they are carburated, and the HO means high output, easily identified by having a 4bbl carb.

I am pretty sure the frame perches are the same, you'll need the rubber mounts that came on the 351w. the bell housing is the same, you'll also need a 351w flexplate/flywheel. I think the accessories are the same, but the brackets are probably different, since the 351w has a taller deck.

 

Thank you to everyone who offered advice. I need some more desperately...

Got it running well, idling nicely, then the high pressure fuel pump went and I had gas all over the ground. Replaced that and a couple of days later it suddenly started running really bad while I was carrying a heavy load.

Had no time so dropped it off at my favorite garage. They tell me I have 140 lb compression in 5 of my 8 cylinders but only about 85 lbs in cylinders 2, 3, and 5. Told me they suspect it is a valve train problem (entirely possible because of how long it has run propane) but before agreeing to replace the entire engine ($5,000 installed is what they told me), wondering if anyone has any sage advice as to what to check.

I think I will bring the truck home tomorrow (at below 1500 rpm it does run like only 5 cylinders are working properly) and will let it sit and will do my own teardown and investigation. Is there any way this could have been caused by an intake manifold problem? I ask because when I took it off it was almost possible to remove the bolts by hand. I torqued them back down to factory spec but wonder if the manifold had been warped by being so loose before and may have leaked after I reinstalled it.

 

No, the intake won't cause the compression problem. It could cause it to run bad but nothing to do with the compression.

The quickest way to determine where the compression is going is to remove a valve cover, the driver side because #5 would be easier, then turn the crank until both the #5 valves are closed. Hook up an air compressor to the spark plug hole and fill the cylinder with air. Listen to where it is escaping from.

If it escapes into the intake it's an intake valve, through the exhaust it's an exhaust valve. If it escapes into the crank case (listen to the dip stick tube) it's a piston or rings.

If it indicates a valve you have just saved a bunch of money, as the only thing needed is head work or head replacement.

Good luck!

 

I agree with 90f150moneypit do the compressed air test first. Either way don't pay $5000 to have them install a $1100 reman motor. If you where brave enough to jump in and take the intake off and mess around then you will have no trouble installing an engine, time consuming yeah a big deal no. I know a fair bit about engines and how they work made it my obsession to learn as much as possible and what goes where but I have never been in a mechanic shop but a couple of times to get tires or exhaust done and I did the swap in 8-12 hours total thats pulling it and dropping in new one and firing it up by my self taking my time and making sure everything was so, if I can do it anyone can, obviously it was easier because I have a carb so I would expect it to be a little more difficult with the efi but you have already taken that apart so the bulk of it you have already done. Can you imagine the motor you could build for $5000 and install your self? Side note if it turns out to be the heads, you can get reman ones fairly cheap, or would be a good time to upgrade. You probably know all this I thought I would throw it out there, kind of a pep talk. ha ha Good luck with your truck

 

I strongly agree with the 84-87 351-W H.O. This is a SUPER motor that runs strong. It comes with a Ford Holley square bore, I think about 600 CFM. It also has mods to the heads that improve performance and heavier duty C-rods. The nice thing is that it is a virtually identical swap except for the flexplate/flywheel...maybe exhaust.

The difference between the 302 and 351-W H.O. is...well words can't even describe it. The engine ROCKS!

 

I don't want to start an arguement or anything but I thought the only difference between the 351w and 351w H.O. was the H.O. has a 4bbl intake and carb. The cams are listed the same, first time I have heard connecting rods are better and the heads are reworked. Later

 

Not a biggie...no argument. I recall reading a technical article somewhere when I once owned a 351-W HO. I will try to locate it and give you the specifics.

 

Reason I mention that is someone read the tech manual on here and they stated everthing was the same. However they do list the connecting rods for the 351w and lightining 351w as having either blue or red coded connecting rods as they have different opening sizes but doesn't mention strength difference. Who knows, later.

 

Wow, thanks for all the advice. Man this is the best site I have found in years and you guys are great.

I will do the air compression test sometime this coming week and report my findings. I'm a bit worried that it actually might be a lower end problem -- maybe that earlier knocking and rough idling problem was a broken piston pin or something?

Anyhow will let you know what I find. If it is just heads I have located dual fuel heads with properly hardened valve seats for $360 each. If it is bigger, I'm thinking I'll go wrecker hunting for a 351W as suggested by bremen, especially if native says the difference is that big. This is an extended cab long box 4X4 and I wondered from the start if a 302 was too small for this size of truck.

 

Thought I would update all the thoughtful people who have been helpful.

Busted a wrist pin (second 302 I have had that has done this) so have decided to get rid of dual fuel and convert to 351W with gas only.

Am reinstalling second gas tank after tossing propane, and switching motor mounts so the 351W will fit.

Do I need to do anything about the hookup to the tranny? exhaust manifolds? and can I just get rid of the whole air induction system?