Engine intake is popping...

Hello,
I put this in the Pontiac forum a few weeks ago, but no one seemed to be able to help with this problem. I know many of the Camaros have the same setup.

My daughter's 1995 Firebird with 3.4L is having a peculiar problem. It backfires through the intake when you rev it up from idle. It is not real loud, but minor explosions easily heard and felt when you place your hand upon the air plenum and air intake duct. Seems to be using a lot of fuel too. Low on power.
I changed the timing gears, chain, replaced both heads with rebuilt heads, camshaft sensor, all three ignition coils, plugs, plug wires, and have extracted one code from the computer. It is "36 24X signal error". I looked in my Haynes book and that code says " (36) Faulty circuit error from coil packs to module".
Looking at that code, I rushed off to the store and bought a new ignition module. But, there was no change.
Any ideas would be appreciated.
Thanks,
Alton

Check for vacuum leaks. You can use a propane torch (not lit) and direct the propane around all of the places a leak could occur. If the idle quality changes while doing this, you've found a leak. Keep checking around until you've identified all of your leaks.

This might sound dumb, but are you shure the timing is set correctly? Have you checked the charcole canister filter? EGR and PCV valve?

I replaced the timing chain and gears and feel they are installed correctly. As far as the ignition timing is concerned, this engine has no distributor to turn and apparently uses the computer to fully control the ignition timing. Unless someone knows of a way to adjust the ignition timing.

I will try the propane torch on the intake.

Thanks for the ideas and I welcome any more anyone may have.
Alton

Hello,
I put this in the Pontiac forum a few weeks ago, but no one seemed to be able to help with this problem. I know many of the Camaros have the same setup.

My daughter's 1995 Firebird with 3.4L is having a peculiar problem. It backfires through the intake when you rev it up from idle. It is not real loud, but minor explosions easily heard and felt when you place your hand upon the air plenum and air intake duct. Seems to be using a lot of fuel too. Low on power.
I changed the timing gears, chain, replaced both heads with rebuilt heads, camshaft sensor, all three ignition coils, plugs, plug wires, and have extracted one code from the computer. It is "36 24X signal error". I looked in my Haynes book and that code says " (36) Faulty circuit error from coil packs to module".
Looking at that code, I rushed off to the store and bought a new ignition module. But, there was no change.
Any ideas would be appreciated.
Thanks,
Alton

This is just a thought , Have you checked the air intake control sensor. Or maybe the o2 sensor. These are just some ideas that could give these kind of problems. I always like to think simple it seems to be cheaper if your lucky.
Good luck , i hope you figure it out.:2cents: :2cents:

There is a possibility that the ignition coils could be bad.

And now that I think about it, other possibilities include:
Cam Posistion sensor
Crank sensor (3x)
Crank sensor (24x)

If you need to know a description of what each sensor is for, then let me know.

Actually, according to my manual which specializes on the 3.4L, code 36 which you pulled means that the ECM is not detecting proper information from the 24X crankshaft sensor. "The 24X signal rpm should be the same as engine rpm up to about 2,000 rpm at which time it stops. Basically, the ECM uses the 24X crankshaft sensor to allow better fuel delivery and spark control while the engine is at idle and up to 2,000 rpm's. So my question is, does the engine feel like it's running fine when it's above 2,000 rpm? If so then that points all signs to this being your problem. If not, then it's always worth a shot at replacing the sensor anyway. And if that still fails, then I would recommend replaceing the Cam Posistion sensor and the Crank sensor (3x) that I mentioned in my last post. Good luck and hope this helps you out some.

I would like to thank all you guys for your suggestions on this car. I just got the car back from my daughter today and will get back to work on it tomorrow. Another mechanic looked at it and couldn't figure it out either.

The crankshaft sensor has me interested. I did not replace that. I also did not realize there are two of them. I only saw one when I had the engine apart to replace the timing set. I will check to see if the engine sounds good at 2000 rpms. In my Haynes book, it calls the two crankshaft sensors 'high resolution sensor" and "low resolution sensor" in the wiring diagram. More confusion for me. Could a faulty crankshaft sensor cause the backfiring through the intake manifold?

Thanks,
Alton

The crankshaft sensor has me interested. I did not replace that. I also did not realize there are two of them. I only saw one when I had the engine apart to replace the timing set. I will check to see if the engine sounds good at 2000 rpms. In my Haynes book, it calls the two crankshaft sensors 'high resolution sensor" and "low resolution sensor" in the wiring diagram. More confusion for me. Could a faulty crankshaft sensor cause the backfiring through the intake manifold?

Yes the Haynes manual is correct, but in technical terms, the crankshaft sensors are known by the 3x crankchaft sensor and the 24x crankshaft sensor.

The 3x (low resolution) crankshaft is located next to the knock sensor and it's signal is mainly used during cranking. The ECM provides three prime pulses at all the injectors based on the 3x signal for start up. It then looks for the falling edge of the can signal to trigger injector number 4. After this the ECM primarily uses the 3x signal from the ignition module to time the sequential firing of each injector

The 24x (high resolution) crank sensor is located next to the crank dampner and has a unique role in fuel control. This is because the 24x contributes to filtering of the MAP signal at speeds below 3000rpm. The ECM reads MAp output at each 24x reference input signals, then averages MAP over every four counts to provide a more stable MAP reading for fuel control. The IAC valve posistion is not longer used to calculate air flow at idle for fuel delivery. So overall, this form of speed density fueling is being used at idle, and at higher engine speeds. This was all done to improve engine starting as well as cranking and idle quality.

As for your question.... Absolutely a bad crank sensor could no doubt cause backfiring. The 3x crank sensor controls fuel delivery at startup, and then takes control of the whole SFI process. While the 24x crank sensor is there to control the fuel delivery at idle and then up to 3000 rpms. And seeing that you've already pulled code 36, which basically means that your 24x crank sensor isnt doing its job for some reason. That would then in turn cause the fuel delivery to each cylinder to still continue operating, but not accurately. Hence, a misfire.

Does the car start up fine with no problem? Have you taken it for a test drive to see if it still misfires/backfires? If it drives fine over 3000 rpm, then that absolutely tells you the 24x crank sensor is the problem.

I took the car for a drive this morning and it has the same problem at all speeds when you put pressure on the accelerator.

So, I stripped the intake, etc off the top of the engine. The camshaft is bad. No lift lobe left on #5 exhaust. Some of the others may be damaged. I have the camshaft ready to pull, but the oil pump drive won't draw out of the block. I removed the hold down bolt and retainer. The oil pump drive will turn freely, but will not come out. Any ideas? How about dynamite!

I wish this had been something simple...but at least I know what is wrong now.
Thanks,
Alton