Backfiring, why?

[FF33rod]

Okay, so managed to have a first start a week or so ago but didn't have the cooling system finished off so I couldn't run it much at all. So now have that in place and put the mufflers on it so that I could run it in for 20 minutes or so. Gotta say, not a whole lotta difference adding the mufflers! But the problem I have is the engine starts fine and then after a few second I start here "pops", it starts backfiring. Seems to get worse the longer I let it run. I double checked distributor relative to TDC, seems to be close. Then as it was idling I moved the distributor around a little to see if it would help, it didn't. What now?

Setup - Ford 347, short block with Trickflow Stage 2 cam installed from TRE performance, AFR 195cc heads, Edelbrock RPM Air gap manifold, Holley Sniper and Holley Hyperspark distributor and ignition....

This is a brand new engine, so I do not have an old standard ignition system to put on it to start off. Have to run with the Sniper controlling the timing. Followed the setup procedure for the Sniper - running the setup wizard sets displacement, # cylinders, etc. As I said, starts fine but then.....

Is there any chance the dizzy is 180 degrees out of phase? I have zero experience in building engines but I thought that if it's 180 out then it wouldn't even start. Not sure what else to try though....

Suggestions please. Thanks guys
Steve

Edit: note that a video has been added, post 24 below which demonstrates the "popping" issue much better than can be described in a post

[David Hodgkins]

Check the firing order.

Ask me how I know.



5/7 EDIT: Adding pic for reference by future readers:

[FF33rod]

Thanks David, looked at that too. CCW rotation, 1-3-7-2-6-5-4-8. Have a Ford Racing wire set with numbers on it, double checked at both the dizzy and the heads....

[wrp]

No experience with Ford but +1 on David's suggestions. In my own endless frustrations I have discovered valves too tight will backfire, lean conditions will backfire, and misadjusted timing will backfire. I have found problems in the Holley accelerator pump, the idle transition, base versus total timing and the curve, the curve ramp, secondary springs not coming on right among the villains. One tremendous issue I had was believing that my distributor was installed correctly when it was one notch out. Also had problems getting it 180 degrees out.. If it isn't the firing order bring her to TDC on number one, make sure the timing mark matches TDC on the arrow. This is the fun you signed up for. Also read your plugs once you've run it a few minutes

[Railroad]

Some people describe, popping out the exhaust as back firing. I think it is popping back through the carb or intake. Which you are describing might give more insight to the problem.

[JimLev]

Have you checked fuel pressure?

[GoDadGo]

Some people describe, popping out the exhaust as back firing. I think it is popping back through the carb or intake. Which you are describing might give more insight to the problem.

An air leak into the exhaust system can also create popping too.

Good Luck!

[mburger]

Any chance the cam firing order is incorrect for your engine?

[Bob Cowan]

If the firing order was incorrect, it would misfire from the very start.

Almost the same thing with valves too tight. It would be a good idea to go back and re-adjust them.

It's possible you have an air leak at the header flange. As they warm up they change shape and it becomes noticeable. If you're using a gasket instead of silicone, check the bottom of the ports, where you can't see well.

A lean condition is most likely. At first start, the enrichment cycle has it running a little fat. But as it warms up it leans out. Add 5-10% to the base fuel map and see what happens.

[HVACMAN]

Thanks David, looked at that too. CCW rotation, 1-3-7-2-6-5-4-8. Have a Ford Racing wire set with numbers on it, double checked at both the dizzy and the heads....

If I remember correctly some of the fords used 1-5-4-2-6-3-7-8

[TxMike64]

I would guess it's too lean or the plugs you are using are too hot in heat range.

I'm assuming this is an HO/roller type engine, which has a different firing order than a non-HO/flat tappet type SBF. If it was a non-HO cam, I don't think it would start.

[FF33rod]

Thanks for the suggestions so far guys

Yes, it's a roller 302 block as a base, stroked and prepped by TRE Performance https://treperformance.com/i-133556-...ort-block.html

Fuel pressure is fine, pump runs fine, I have a gauge on the input to the Sniper and it's reading around 60psi

Some 302s have a different firing order, the HO and (I think) the 351W are different. Called Trickflow and verified that 51403002 is indeed 1-3-7-2-6-5-4-8

The suggestions about a lean condition is resonating with me. The first few seconds after initial start everything seems okay - likely because of the fuel shot that the Sniper puts in the manifold before the engine turns over. Then after that the backfiring (or popping or...) starts and seems to get worse until I shut it down a few seconds later.

Wondering if the cam selection - stock/mild vs streep/strip will be affecting this. I think I selected stock/mild as Holley suggests starting there if you're unsure.
Going to search out the Holley Sniper troubleshooting guide....

[TxMike64]

Just for future readers:

260/289/302 firing order is 1-5-4-2-6-3-7-8
302(5.0)HO/351W firing order is 1-3-7-2-6-5-4-8

[wrp]

I would certainly look at the header mounting to the block, fact is look for exhaust leaks in general. I also highly think looking at the heat range of the plugs is a definite suspect, Did you read the plugs yet?

[Norm B]

Another suggestion, look for intake manifold leaks. They can cause a lean condition on one ore more cylinders resulting in popping out the exhaust.

HTH
Norm

[Papa]

Another one in the exhaust leak camp. I fought a similar problem with the first headers I tried. The driver's side wasn't flush to the head and that was causing popping on my car. Once I got a good fit on the headers, the issue was gone.

[FF33rod]

Recommended starting point for plugs was Autolite 3924. Trying to figure out where in the heat range that is wasn't the easiest but it seems its slightly to the higher side (only 4 in the range and it is 3rd hottest). The Champion equivalent to that is supposedly RC12YC which is what I've used. These are basic Copper resistor plugs.

To be honest, I'm afraid to leave it running for more than 5-10 seconds as it gets quite crazy (I'd say violent). I'm afraid of damaging something. Not sure how to assess for leaks as suggested. I guess I could poke around with a feeler gauge or something when it's not running.

I can see how an intake leak would play with mixture and cause problems but how would an exhaust leak at the head or otherwise cause a problem?

Steve

[wrp]

It misreads your 02 and the fuel tables are then off. You may not have enough time on the engine to make anything of the plugs but here is a visual on things you can tell if you read them

http://www.4secondsflat.com/Spark_plug_reading.html

[wrp]

Again your engine is so new many of the telltales might not be that obvious. Black soot around the header flanges are a good indication. I am not familiar with the EFI, on the SBC I would just hook a manifold pressure gauge up to it. Crank it up in the dark, put a camera on it see if you notice cross firing. What you are describing sounds seriously like an ignition problem. They will start 180 degrees out, at least Chevies and Mopars will. What does TRE say?

[FF33rod]

Again your engine is so new many of the telltales might not be that obvious. Black soot around the header flanges are a good indication. I am not familiar with the EFI, on the SBC I would just hook a manifold pressure gauge up to it. Crank it up in the dark, put a camera on it see if you notice cross firing. What you are describing sounds seriously like an ignition problem. They will start 180 degrees out, at least Chevies and Mopars will. What does TRE say?

Ok, being able to start wen 180 out is not something I knew or expected. Didn't think it would happen so I haven't seriously investigated that. Step 1 after work today... Thank you sir.
Was going to contact TRE today but will hold off now.

[wrp]

When mine was out the symptom was a wildly erratic back fire. However, even one notch off can bring on serious backfires. I hope you Ford guys are not laughing at me and I hope you realize my total experience iw with chevies but I did have to climb this mountain. I ruined my first engine before I got it right

[NAZ]

FF33rod, it's extremely difficult to troubleshoot even simple issues over the internet but a clear description of the symptoms will help. When you say "backfire" what does that mean to you? If I understand, seconds after starting you hear "pops" -- where is that coming from? Exhaust? Intake? Yes it makes a difference. If you hear and visually see evidence of backfiring out the throttle body (intake) the root cause is very different than if you hear a popping noise out the exhaust.

You're getting lots of ideas here but they are scattered all over the place. Try to be very specific in describing the symptoms. Or better yet, take it to a shop you trust -- you need help, and this is the most direct way to get it. You put the monkey on the back of the mechanic and he will follow a systematic troubleshooting approach to identifying the problem. Since this is a 302 based engine I'd recommend a Ford dealership. I've been troubleshooting engine problems for half a century and made my living at it as a Ford technician and I can't determine if you are really experiencing a backfire condition or a "popping" noise out the exhaust. Two totally different issues.

If it is backfiring (combustion in the intake tract) the two primary causes are timing too advanced or leaking intake valve. The fire starts in the combustion chamber and even on a very radical cam the intake closes 30-degrees before the spark is initiated at full advance. A backfire is caused by the combustion ether taking place before the intake valve closes (way advanced) or the valve is leaking igniting fuel in the intake. There is no other source of ignition in the intake tract.

If you haven't verified that your timing pointer is reading zero at actual TDC (requires a TDC finder) then you are simply guessing at your base timing and could actually be very different than what you believe it to be. Since this was a short block build with aftermarket heads you supplied that means you had to spec the correct length push rods and should have verified that the engine builder correctly timed the cam. And the hydraulic lifters have to be adjusted correctly. A grossly mis-adjusted lifter can hold open a valve. And since this is a roller, the cam requires a button to limit end play -- if end play is not correct your timing will wander as the cam end play will affect the distributor motion. Couple that with incorrect base timing and you may be way too advanced on the ignition lead. Erratic timing can be picked up with a timing light as your lead will move around during steady idle.

[FF33rod]

FF33rod, it's extremely difficult to troubleshoot even simple issues over the internet but a clear description of the symptoms will help. When you say "backfire" what does that mean to you? If I understand, seconds after starting you hear "pops" -- where is that coming from? Exhaust? Intake? Yes it makes a difference. If you hear and visually see evidence of backfiring out the throttle body (intake) the root cause is very different than if you hear a popping noise out the exhaust.

You're getting lots of ideas here but they are scattered all over the place. Try to be very specific in describing the symptoms. Or better yet, take it to a shop you trust -- you need help, and this is the most direct way to get it. You put the monkey on the back of the mechanic and he will follow a systematic troubleshooting approach to identifying the problem. Since this is a 302 based engine I'd recommend a Ford dealership. I've been troubleshooting engine problems for half a century and made my living at it as a Ford technician and I can't determine if you are really experiencing a backfire condition or a "popping" noise out the exhaust. Two totally different issues.

If it is backfiring (combustion in the intake tract) the two primary causes are timing too advanced or leaking intake valve. The fire starts in the combustion chamber and even on a very radical cam the intake closes 30-degrees before the spark is initiated at full advance. A backfire is caused by the combustion ether taking place before the intake valve closes (way advanced) or the valve is leaking igniting fuel in the intake. There is no other source of ignition in the intake tract.

If you haven't verified that your timing pointer is reading zero at actual TDC (requires a TDC finder) then you are simply guessing at your base timing and could actually be very different than what you believe it to be. Since this was a short block build with aftermarket heads you supplied that means you had to spec the correct length push rods and should have verified that the engine builder correctly timed the cam. And the hydraulic lifters have to be adjusted correctly. A grossly mis-adjusted lifter can hold open a valve. And since this is a roller, the cam requires a button to limit end play -- if end play is not correct your timing will wander as the cam end play will affect the distributor motion. Couple that with incorrect base timing and you may be way too advanced on the ignition lead. Erratic timing can be picked up with a timing light as your lead will move around during steady idle.

NAZ, totally understood. I was already thinking along the lines of one of your key points - how does anyone really know what I'm referring to? I was thinking that a video or sound recording would help.

As for going to a Ford dealership, I'm pretty sure that I would be either stared at rather dumbfounded or be laughed at. That's not a knock on Ford but a statement on most dealership "mechanics" these days. With your experience and the era that you got your training, you're a true mechanic. Most these days need a place to plug in a computer and then they follow the instructions on the computer whether it makes sense or not. I could tell you some stories about BMW but you probably have similar ones of your own. Best idea I think would be to get an independent mechanic shop to look at it. However, I'm hoping it won't come to that.

As for all the parts playing together, except for the Holley Sniper and the "dress up" bits, I made it pretty simple by using a top end kit on top of a short block, both from TRE. So all pieces were known to perform well together and would fit. Yes, I properly adjusted hydraulic lifters, etc. So hopefully, I won't be discovering any issues in these areas.

Thanks again, I will be looking at the 180 possibility tonight and you'll be darn sure I'll report back.

Cheers, Steve

[FF33rod]

Okay, so your typical good news, bad news scenario.

First the good news. Redid the TDC location, no problem there. Rotated the engine and made sure #1 was on compression before hitting TDC, checked where the rotor was on the distributor - right where it should be, pointing at #1 wire. I have to say I was a bit disappointed, I wanted to find the problem!

So, after that I rechecked the Sniper wizard settings and all seemed fine. I rerouted the wires coming out the distributor going to the CD ignition so they didn't run parallel to the coil output. Setup the camera and went for a start.

The engine ran much longer before the popping this time. I'm going to guess that was due to multiple primer shots from the Sniper before I actually went for the start. The Sniper does a primer shot when it power up and I did at least 2 of those power cycles before turning the engine over. The first "pop" occurs around 15 seconds, then you can start to hear multiple pops going off from 25 seconds onward. The AFR seems to be spiking with each pop, sometimes showing a yellow or red background on the AFR number. Video resolution was dumbed down when I uploaded so it's difficult to see the AFR number on the Sniper display. The numbers were all higher than target; 12s, 14s and the odd high teens or 20. Not supposed to be way up there. The fuel pressure is remaining constant through out, input to the sniper when the pump is running is about 75 psi.

Will be getting in touch with TRE tomorrow and Holley - if I have time, work is getting busy.

[RickP]

where is your O2 sensor located?

[wrp]

Have you considered bad fuel?

[FF33rod]

O2 sensor is in the FF provided J pipe, passenger side

Fuel is 94 octane bought a week ago

[FF33rod]

TRE is no help, they have no experience with the Sniper...

[mike223]

Take the valve covers off and see if someone failed on polylock installation (loose rockers or rockers off / out of position).

Don't ask me how I learned that...

[Jeff Kleiner]

After seeing the video I'd be suspicious of the fuel injection system.

Jeff

[FF33rod]

After seeing the video I'd be suspicious of the fuel injection system.

Jeff

Thanks Jeff, anything in particular?

[mike223]

After seeing the video I'd be suspicious of the fuel injection system.

Jeff

I tend to agree, but I got to thinking if he had kicked a rocker or pushrod and had one exhaust valve that wasn't opening....


It *might* act like that...

[ztoolman44]

I too would suspect the fuel injection system. The fact that it starts fine and runs then deteriorates till it stops rules out a lot of things that I was considering initially like timing or cam gear or distributer gear. Other option could be the ignition box having issues. Seems electrical of some sort.

Looks like fuel pressure is good so that helps to rule out stuff.

[ztoolman44]

AFR can be messed up if the firing is off from a glitch somewhere and you are getting incomplete or absent firing in the cylinders

[Papa]

What type of ignition are you using. There are very specific wiring instructions for the Sniper depending on your ignition type.

[FF33rod]

To be clear, the engine is stopping because I kill it. Not wanting it to run long with whatever is wrong.
Ignition, as mentioned above, is full Holley kit - HyperSpark dizzy, coil and CD ignition.

[Papa]

This video is pretty good for guiding through the sniper install with a timing control distributor.



Not sure if it will help, but with the timing control distributor/ignition, you could be experiencing a timing issue being driven by the ECU.

[Papa]

Here is another video specific to the Hyperspark ignition:

[Houdini]

if you got a dial back timing lite it would be interesting to see what the timing is running at

my uneducated ear makes me wonder if you have some detonation just not running too smooth

I am going to put injection on my ford and it scares the hell out of me, im going to carb it untill I finish it all out
hope you can find the problem, they can drive you almost crazy

[idoxlr8]

Steve,
Seems to start fine and then gradually gets worse. Rules out timing issues I would think.
Those AFR readings are crazy lean when it starts popping and makes sense. Why it’s leaning out is another issue. Can you data log it?