Backfire during acceleration : 5.0L EFI

[jakester888]

1993 5.0L EFI motor with 24# injectors and 24# MAF. Timing set at 10 BTDC without spout. Idles fine. But under acceleration large backfire on passenger side.

What are the possible causes?

My guess : using original 90lph fuel pump. I have a new one (155lph) but have not installed.

Do you agree? What other possible causes?

[Olli]

Exhaust leak(s) another possibility.

Olli

[cobrafern]

Are you spark plugs in the right order

[Carlos C]

Man, you're not having much luck with this. Ok, let's go again. What kind of performance work have you done to the engine? If it's basically stock, a larger pump (or the larger injectors and MAF sensor you already installed) won't matter. As long as you already verified the timing, as per your other thread, confirm that you have the correct firing order (1 3 7 2 6 5 4 8). Also, make sure that the #1 cylinder wire is attached on the distributor's plug with the "1" on it (at the 12 o'clock position, if looking from the front of the engine). The only exeption to this is that some aftermarket distributors have the #1 wire plugged at the 9 o'clock position instead. Mine does. This will be noted on the distributor's instructions. If you have a stock distributor, disregard this.

If all that checks out, check that you're getting a strong and consistant spark to all the cylinders on the right bank. There's a tool you can get to do this. Many marine shops and some auto parts stores sell it. Otherwise, being very careful, you can attach a spare spark plug to one of the wires while the engine is off, trip the fuel pump (you just want the engine to turn over and not start), and ground the spark plug body to the car's frame. Turn the engine over and check. Repeat on the rest of the wires. If all the wires check out, do the same test with the engine's spark plugs, one at a time. Try these tests and let us know the results. Good luck... Again.

Carlos

[skullandbones]

This is not a fuel pump issue. Do you have stock rockers, heads or something like adjustable rocker arms or other after market components? If you have the stock screw down rockers then you also need to verify that you have the stock push rods that belong to that engine (you didn't mix and match). Verify that the valve lash is as expected. If you have adjustable rockers also verify that they have the correct clearance. If this is good then it's probably a firing order or timing issue. You are having more than your share of issues with this 5.0 but it will sort out, I'm sure. Good luck,

WEK.

[Walt]

I went through this with my 93 mustang , would back fire out the intake and stall , but idle fine. Turned out to be a bad MAF .

[jakester888]

OK, here's what I verified:
1) Spark coming to all cylinders - I bought one of those spark visualizer tools at Autozone. Easy to see spark at all 8 cylinders.
2) Validated firing order : 1-3-7-2-6-5-8, where 1 is at "1-o'clock" position.
3) Validated timing with/out spout at 10 BTDC. With spout it's about 14 BTDC auto-adjusted.
4) Added exhaust gasket to the passenger side exhaust where it connects to the J-pipes. <-- this seemed to solve the popping at acceleration (thanks Olli).

Now, as you can hear in this video, there is still a popping noise at idle in what sounds like the passenger side lower intake manifold. Any ideas?


http://youtu.be/hfXYABYkPQw
Ignore that sound at 42sec and 50sec, that's the exhaust bracket rattling around, I haven't fastened that down yet.

My next thought : try a new set of spark plug wires and maybe look at MAF again.

[CHOTIS BILL]

What has happened to number 4 spark plug? I assume that is just a typo.

Bill Lomenick




OK, here's what I verified:
1) Spark coming to all cylinders - I bought one of those spark visualizer tools at Autozone. Easy to see spark at all 8 cylinders.
2) Validated firing order : 1-3-7-2-6-5-8, where 1 is at "1-o'clock" position.
3) Validated timing with/out spout at 10 BTDC. With spout it's about 14 BTDC auto-adjusted.
4) Added exhaust gasket to the passenger side exhaust where it connects to the J-pipes. <-- this seemed to solve the popping at acceleration (thanks Olli).

Now, as you can hear in this video, there is still a popping noise at idle in what sounds like the passenger side lower intake manifold. Any ideas?


http://youtu.be/hfXYABYkPQw
Ignore that sound at 42sec and 50sec, that's the exhause bracket rattling around, I haven't fastened that down yet.

My next thought : try a new set of spark plug wires and maybe look at MAF again.

[jakester888]

What has happened to number 4 spark plug? I assume that is just a typo.

Yes, type-o. 1-3-7-2-6-5-4-8.

Another thought : since I did replace the upper & lower intake manifold, could this sound be a bad seal or leaky gasket at lower intake?

[jakester888]

Problem solved! It was an air leak at the upper intake manifold.

Replaced the spark plug wires : no help.
Replaced the gasket between upper & lower intake then put some gasket maker material on the EGR delete & presto! No more pops.

[jakester888]

Sounding better all the time. Now the pop is on the driver's side. I believe it is the exhaust where it connects to the J-Pipes... I need to add the gasket at that point as well. Idles much better and starts right up now.


http://youtu.be/oGVYIeBryzU

[Carlos C]

Jake:

Great to see that you're getting this engine figured out. It definitely sounds better, and idles smoother. Good to know that it wasn't anything expensive, but at least you were able to verify that the ignition system is working properly. That tool will come in handy in the future... trust me.

That faint popping sound on the driver side should be another gasket. Another very useful tool I recommend is a mechanic's stethoscope. Even a medical one works well. It can help you pin-point the source of pings, knocks, and pops.

Carlos