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Engine backfires...

2K views 23 replies 5 participants last post by  DPW 
#1 ·
Hi guys and gals, I have an 84 w150, the truck has had an engine swap to a 78 440. It ran good until I tried to park on a hill. Facing downward, I put the truck in park, then I let off the brake, and what sounded like the transmission slipping. Like gears grinding very slowly. Now when I try to accelerate fast the truck backfires like crazy, but not when I accelerate really slowly? Any help on what this is or what I should do to fix it? Could it be my timing?
 
#3 ·
Alrighty, I am completely new to working on trucks, and vehicles for that matter. How would I go about checking my timing and distributor? I believe you helped me out with my ignition problem a while back too, thanks for that.
 
#5 ·
sounds like timing to me. if you are worried that the timing chain slipped....find top dead center.......mark your #1 plug on the distributor then turn the crank with a wrench till the mark on the harmonic balancer aligns with the timing mark at zero on the timing chain cover. pull the dizzy cap off and see if the rotor lines up with the #1 mark you made on the dizzy. if the rotor is 180* out then turn the crank over one complete rotation and see if the rotor lines up with your mark. if its not lined up then the chain slipped.

that grinding noise could very well be the park pin slipping.....but ya, i'd check the timing, make sure its where its supposed to be, then check for TDC, then check for vacuum leaks after that.
 
#7 ·
bring it, i'm sure everyone here is more than willing to help out
 
#8 ·
x2 on timing/ignition.

Being parked on a hill doesn't help that carb much, either. I've had a couple rigs vapor-lock being parked on hills and going up a steep hill before. Once on a boat launch... Bad day...

Wouldn't hurt to investigate the coil and plugs, either. My Jeep had a plug cable melt and ground-out on an exhaust manifold intermittently. I didn't figure it out for a couple of trips. It had a lot of similar symptoms you are facing...

Backfiring is an igntion-timing and/or fuel-delivery issue.
 
#9 ·
I park on flat ground. The day I went to park on a hill, I saw about a 200 inch whitetail, put it in park to grab my binos, and then it slipped. I never park on hills, mainly because my park brake doesnt work. I'll do the timing tomorrow after work.
 
#10 ·
Holy shit, I've been looking at some youtube videos on how to replace a timing chain... am I going to have to take the engine out of my truck to do it? There is no way I am bringing my truck to a shop. I want to do everything on my own. I am just wondering, is it bad for me to be driving my truck with bad timing? Because if it isn't I would rather wait until the spring when I have a bunch of money saved up and a motorcycle to ride, to work on it. I will pull the distributor cap of tomorrow and check my timing chain though. Dam this truck.
 
#11 ·
you dont have to pull the engine but it's serious work. investigate everything else before considering timing chain. that's the worse case scenario
 
#12 ·
Could be a bad distributor cap or moisture in the distributor. How long since the cap and rotor have been replaced?
 
#13 ·
Okay so I checked my timing chain by taking the distributor cap off and watching. It's about 1/16 turn before it starts to move. I will post a pic of my distributor when I get home. Also another thing I might add, someone jacked my gas cap, it's been off for a while now. I made it out of aluminum, I guess thats why they took it. could the backfires be because of moisture on my fuel?
 
#14 ·
what do you mean by 1/16th turn? water could be the culprit. get a bottle of water dryer and dump it in the tank
 
#15 ·
you'd probably see a lot more play than a 1/16th of an inch if it was bad. the thing to do is turn the engine, stop, then turn backwards and see how much the crank turns before the rotor turns.

start with the easy stuff first, spark plugs, spark plugs wires, cap, rotor, the water thing, coil. get a vacuum gauge and check to see how much vaccum you are pulling. stuff like that, the simple stuff.
 
#16 ·
Oh sorry for the confusion. By 1/16, I meant when i took the cap off, turned the motor forward until it started to move, then it took about 1/16 of a turn going backwards for the thing to start moving again. I am going to get a bottle of that water dryer and see what that does. Today coming home from work it didnt back fire once. Almost makes me believe it's the water in my fuel? It seems when I have a fresh tank of gas that my engine runs fine. Still no power, but no backfires as well.
 
#18 ·
that's your coil. sends the spark to the distributor. the silver thing on the distributor is called a vacuum actuator, just so you know.

edit: ok i'm going to leave that there...wow my brain is fried. vacuum advance.....not actuator
 
#21 ·
no, vacuum advance uses vacuum to change the timing inside your distributor. this has nothing to do with adjusting your timing like i mentioned in your other thread, by the way you should just stick to one thread from now on with all your questions. easier that way. a vacuum gauge will tell you how much vacuum you have and you'll need to find a vacuum port for that. from the intake manifold, not from the carb.

the screw adjustment varies depending on the carb you have. always best to start with a general turn amount (like you mentioned). look up your carb and find that amount. best way to adjust the mix is to hook up the vacuum gauge and adjust the mix until you achieve highest vaccum possible. just work one screw till you find the highest vacuum, then go to the other screw until you find the highest vacuum with that screw......done. if you have a vacuum leak, the vacuum gauge will show low vacuum and you should fix the leak before adjusting the carb. what the numbers are for proper vacuum for a 440....i dont know.

if you have a vacuum leak, get a can of starting fluid and spray around the intake manifold, base of the carb, and any vacuum hoses. if you hear the engine rev, you found the leak.
 
#23 ·
let me know if you have questions, i work at a shop during the day usually. my boss has a few projects lined up for me over the next few days so i will be busy. i'll help ya out as much as i can.
 
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