backfiring through the intake
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Cargo Master
Joined: Oct 2008
Posts: 2,308
Likes: 1
From: Elyria, OH
backfiring through the intake
96 f250 351w. I pulled the heads off this motor to replace the gaskets. While I was doing so, I put on short tube headers, removed smog stuff due to it being rusted off, plugged holes in back of the heads, New plugs, wires, cap, rotor, y-pipe and 1.7rr. Before I did any of this, the truck ran better than after I "fixed" it. I pulled the codes and get a lean code, but I'm sure it was in there from before due to busted ypipe and leaky manifold gaskets.
I got this thing together thinking that I'm going to have a stout little motor, but this thing is gutless and idles rough. I still have the exhaust leak at the y-pipe, but I cannot see that causing the issue. Fuel pressure is at 38 psi at idle
I got this thing together thinking that I'm going to have a stout little motor, but this thing is gutless and idles rough. I still have the exhaust leak at the y-pipe, but I cannot see that causing the issue. Fuel pressure is at 38 psi at idle
Logistics Pro
Joined: Mar 2005
Posts: 4,698
Likes: 47
From: Mexico, Missouri
Sounds like timing isn't right. I would be sure that the rotor inside the dizzy is facing towards #1 on the cap when the #1 piston is at the "Compression" stroke. Use a piece of tissue paper and plug the plug hole till you find it.
Have you checked that the plug wires are correct for the firing order? I believe this year engine uses 1-3-7-2-6-5-4-8 order.
Let us know what you find.
Have you checked that the plug wires are correct for the firing order? I believe this year engine uses 1-3-7-2-6-5-4-8 order.
Let us know what you find.
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Cargo Master
Joined: Oct 2008
Posts: 2,308
Likes: 1
From: Elyria, OH
I never removed the distributor and it didn't do this prior to me tearing into it. I will triple check the wires. I went to set the timing, but I cannot find the marks for the life of me. They are rusted away. Any ideas?
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Cargo Master
Joined: Oct 2008
Posts: 2,308
Likes: 1
From: Elyria, OH
I made sure that all push rods were seated properly before torqueing the rocker arms down to 14 ft-lbs. I did not however rotate the motor to where the valves were closed when I did it. I was told since the lifters are hydraulic, I did not have to do so. Could this be my problem?
I did remove the cap and wires and changed them they are on correctly. All sensors and connectors are on and good connection.
I did remove the cap and wires and changed them they are on correctly. All sensors and connectors are on and good connection.
Lead Driver
Joined: May 2011
Posts: 5,799
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I made sure that all push rods were seated properly before torqueing the rocker arms down to 14 ft-lbs. I did not however rotate the motor to where the valves were closed when I did it. I was told since the lifters are hydraulic, I did not have to do so. Could this be my problem?
I did remove the cap and wires and changed them they are on correctly. All sensors and connectors are on and good connection.
I did remove the cap and wires and changed them they are on correctly. All sensors and connectors are on and good connection.
this is incorrect. even though they are hydraulic, if the lifter is on a cam lobe it will have to compress the spring regardless of lifter style in order to seat the rocker (im sure you noticed this). this will make the torque measurement inaccurate. I always just tighten them down good-n-tight rather than use a torque wrench. there is no reason to turn the motor over to net your 14lb torque rating, as good and tight is plenty good enough, especially on a low rpm application such as this.
any codes?
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Cargo Master
Joined: Oct 2008
Posts: 2,308
Likes: 1
From: Elyria, OH
So what I did with the rocker arms " should" be okay not to cause a problem? I'll probably pull the intake and valve covers just to check and make sure.
I had 2 codes. One was an always lean code and the other was for the spout. I plugged the spout in and confirmed that it was advancing with throttle and it was.
I had 2 codes. One was an always lean code and the other was for the spout. I plugged the spout in and confirmed that it was advancing with throttle and it was.
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Cross-Country
Joined: Sep 2013
Posts: 64
Likes: 1
From: boonies, central TEXAS
Timing Marks
The timing marks are there. Take some middle grade sandpaper and sand the harmonic balancer until you find them (do NOT use one of the magic rust remover sprays). Once you find them, if you have a scribe, go over them lightly, if not, ehh. Get some liquid paper and go over them gently with a paper towel handy in case you go outside the lines. You should be able to see them great under the light.
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Cargo Master
Joined: Oct 2008
Posts: 2,308
Likes: 1
From: Elyria, OH
I have messed with the distributor advancing it and retarding it and revving the engine at a bunch of different settings and it still backfires through the intake on me.
I will get it to 10* BTDC today after work, but I do not believe that timing is the issue here.
I will get it to 10* BTDC today after work, but I do not believe that timing is the issue here.
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Cargo Master
Joined: Oct 2008
Posts: 2,308
Likes: 1
From: Elyria, OH
It's rather upsetting... trying to help my father out doing this for the price of parts and I mess it up worse than when he brought it to me. I've worked on these engines since I was 15 and thought I knew them pretty well. Guess that's not the case
Logistics Pro
Joined: Mar 2005
Posts: 4,698
Likes: 47
From: Mexico, Missouri
14 lbs torque on the rockers...I'm more technical on the 302, but I would be inclined to think the torque should be higher. I know that on E7TE heads, you torque the rockers to 18-22. Maybe...this is the only other possibility I can think of.
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Cargo Master
Joined: Oct 2008
Posts: 2,308
Likes: 1
From: Elyria, OH
Found my problem... looks like I didn't have the rockers tight enough. Found 2 push rods jumped off of the lifters and bent them. Should I pull the intake to make sure the lifter didn't come out of the bore?