98 Ford Ranger 3.0L Backfire

[Theo]

Hey Folks,

I have a 98 Ranger, 4wd, 3.0 Liter. A couple of years ago I had a head gasket fail. I replaced the heads, gaskets, etc. It did ok. The next year a deer jumped out in front of me and it took all summer to get that repaired. It hasn't been driven a lot the last few years.

Late last year we took it on a trip out west and noticed it was sucking down oil. It's never done that before. Something was going on in the #1 cylinder. The plug was getting fouled. Then it started leaking coolant in that general area. I thought it might be another bad head gasket.

So I took it apart again. The leak problem was the gasket between the left cylinder head and the intake manifold. I replaced the head gaskets again anyway.

I only mention all of this to be clear about how far I dug down into the engine.

It is all back together now. No leaks. It idles ok but if I rev it up even a little I get sharp popping backfires.

Does anyone have an idea of what I might have messed up?

 

[RonD]

Welcome to TRS

Recheck firing order on coil pack and then check it again, then have a friend check it, lol
[3 4]
[2 6]
[1 5]

The 5 6 4 side often gets a wire reversed
[ ] are matched pairs, its how the V6 engine is balanced, 1/5 are both at TDC at the same time, same for 2/6 and 3/4
That's why the wires are the way they are

Backfire means a cylinder misfired and the unburned fuel was ignited in exhaust manifold by the next firing cylinder, so you hear a POP

 

[Theo]

Thanks, I went out and checked it again. If this diagram is correct I have it right.

I did change the spark plugs since I had the cylinder heads out. One was fouled by the leak. Wires are not new but were in very nice shape. I think I replaced those after the original head gasket problem a couple of years ago.

I had the fuel rails and injectors off of course. The injectors seemed ok. I don't smell any gas or see any leaks. Could an injector get stuck open and be allowing fuel in when it's not supposed to?

Both intake manifolds were taken off. The rocker arms were removed and put back in. If I didn't get one of those put back right could it be failing to open a valve and cause a backfire somehow?

Not getting any check engine codes yet.

Theo

 

[RonD]

Wiring is correct in diagram

Yes could be rocker issue, compression test would show that

You would see grey smoke out the tail pipe if an injector was the issue
make sure all 6 got plugged back in but longshot

A vacuum leak in lower intake can cause it, spray some soapy water around intake with engine running, RPMs will stumble if any is sucked in and worst case is a cleaner engine not a FIRE like using a "fuel" to detect a leak, lol

 

[Theo]

Thanks again. Didn't notice any smoke but I wasn't particularly looking for that. I will check.

Maybe I'll replace the wires just to make sure. It sounds to me like for a backfire to happen, at least one cylinder has to be not firing and allowing the injected fuel to get to the exhaust somehow.

A vacuum leak in lower intake sounds plausible.

I appreciate the input. Kind of fried right now.

Theo

Any insufficiently advanced technology is distinguishable from magic - Arthur C. Clarke
Any technology distinguishable from magic is insufficiently advanced - Greg Bear

 

[Theo]

Ok, swapped plugs with old ones. Made absolutely sure the cables are correct. Still popping.

Took the valve covers off and checked the pushrods and rockers. One is definitely bent a little. Another may be ever so slightly bent. They will be replaced. I think those might have been causing some minor clattering noise but not sure it could be responsible for the backfires

No obvious vacuum leaks.

 

[Uncle Gump]

If you have bent push rods... the next question is how did they bend.

 

[Theo]

If you have bent push rods... the next question is how did they bend.

Not sure, but the truck does have 320k miles

 

[Theo]

Pushrods are replaced. I didn't expect that to solve the popping issue but I thought maybe taking it all apart and putting it back together again might shed some light on something.

No dice. Still popping.

There's no gray smoke. Much soapy water applied to vacuum lines with no apparent effect. Wires were changed for good measure.

I'm not a super experienced wrench turner. This was likely something I caused when repairing the gasket. It was not popping before I did that. The only issue then was it was chugging oil and leaking coolant by the #1 cylinder.

I'm not even 100% sure this is actually backfiring. A hand in front of the exhaust when you hear the pops doesn't actually feel any pressure change one might expect with a backfire. Could be wrong but the sound appears to be coming from the front of the truck and not the exhaust.

Here's a short vid of what it's doing on youtube. See what you all think and let me know if it rings any bells. Thanks!

Theo

 

[Theo]

Followup:

I took the engine apart the next weekend and found a pushrod out of place on #1. Not sure how that happened but obviously I didn't put it back together right. Its been fine ever since.