1995 P30 backfiring thru intake when hot

[Cousin_Eddy1]

Hi, wondering if anyone has had a similar problem like this:

1995 southwind 33 ft P30 7.4L TBI with Banks exhaust. 73k miles. Rv gets used alot. Every 3 weeks or so.

Starts loosing power and popping after it is warmed up. Takes about 10 minutes. Wont do it when cold, happens mostly at partial throttle when cruising about 60. Also happens after starting out from a stop. Doesn't seem do it under WOT .

Facts:

1. I removed the banks cold air snorkel, problem was much worse. Points to a lean condition.
2. Idle is perfect. No signs of vacuum leaks.
3. Replaced O2 sensor
4. Replaced MAP sensor
5. Replaced fuel filter.

So, it seems to me that this starts to happen when the computer switches over to "closed loop". That means its using the O2 sensor for feedback. But i replaced that. Does anyone know what else the computer uses to control fuel rate when in closed loop? Or, any other suggestions?

Thanks!

[MrWizard]

Nice to hear you found it..good work

[Cousin_Eddy1]

Turns out, backfiring is a symptom for just about anything not working right on this vintage chitty chitty bang bang motor....including lean condition. The extra O2 in the intake is much more easily ignited. All it takes it a hot valve or something. This is a common symptom if there is a vacuum leak or accelerator pump problem on the super old motors with carbs. In this case it was a plug wire with high impedence, the energy would take the path of least resistance through another wire, firing the next cylinder while the intake valve was still open.

[2bzy2c]

Backfiring is NOT fuel related. In 95% of cases it is an ignition problem. That vintage engine, I would look to the spark plug wires, then the distributor cap.
Keep looking at all IGNITION possibilities. There is no way fuel would cause a backfire on its own. An poorly timed spark (ignition) is causing your problem.

[352]

Cousin_Eddy wrote:
Hi, wondering if anyone has had a similar problem like this:

1995 southwind 33 ft P30 7.4L TBI with Banks exhaust. 73k miles. Rv gets used alot. Every 3 weeks or so.

Starts loosing power and popping after it is warmed up. Takes about 10 minutes. Wont do it when cold, happens mostly at partial throttle when cruising about 60. Also happens after starting out from a stop. Doesn't seem do it under WOT .

Facts:

1. I removed the banks cold air snorkel, problem was much worse. Points to a lean condition.
2. Idle is perfect. No signs of vacuum leaks.
3. Replaced O2 sensor
4. Replaced MAP sensor
5. Replaced fuel filter.

So, it seems to me that this starts to happen when the computer switches over to "closed loop". That means its using the O2 sensor for feedback. But i replaced that. Does anyone know what else the computer uses to control fuel rate when in closed loop? Or, any other suggestions?

Thanks!

Fuel pressure regulator????????

[MrWizard]

do a timing check
cold and after it gets warm and acts up
sounds like timing is off

Cousin_Eddy wrote:
Hi, wondering if anyone has had a similar problem like this:

1995 southwind 33 ft P30 7.4L TBI with Banks exhaust. 73k miles. Rv gets used alot. Every 3 weeks or so.

Starts loosing power and popping after it is warmed up. Takes about 10 minutes. Wont do it when cold, happens mostly at partial throttle when cruising about 60. Also happens after starting out from a stop. Doesn't seem do it under WOT .

Facts:

1. I removed the banks cold air snorkel, problem was much worse. Points to a lean condition.
2. Idle is perfect. No signs of vacuum leaks.
3. Replaced O2 sensor
4. Replaced MAP sensor
5. Replaced fuel filter.

So, it seems to me that this starts to happen when the computer switches over to "closed loop". That means its using the O2 sensor for feedback. But i replaced that. Does anyone know what else the computer uses to control fuel rate when in closed loop? Or, any other suggestions?

Thanks!

[Cousin_Eddy1]

Polar76, journey Indiana, 352, You are the winners of this thread. After my girlfriend kept bugging me to do it, I changed the wires and plugs. She purrs like a kitten now. The RV runs like it was new, too. I have changed wires and plugs 10x before since I was 16 to solve a problem, and it has never worked. It worked this time. All righty then. Thanks!

It started running worse and worse, even when cold at all speeds and throttle positions. So I switched over to replacing ignition parts, like cap rotor and module. Still no change til I changed the plugs and wires. The #2 plug was really carbon fouled, so I am guessing that's the one that was missing.

[Born_To_Travel]

I remember having a similar problem years ago on a GM product... Turned out it was the pick-up coil in the distributor... That is the part that replaced the points in there.. It was a heat related issue as it warmed up it would cause misfiring and worked fine when it cooled down.. Maybe pull the distributor and check it..

[352]

And, take the hose off the throttle body and spray the he!! out of it with carb cleaner. Carbon WILL build up in the body. Recommended one time a year. A probable cause

[Cousin_Eddy1]

Wouldn't ignition issues present symptoms regardless if it was cold or hot, and would present at idle and WOT? Not just at partial throttle and start presenting almost exactly 10 minutes after cold start? Im sure a tune up is due, but can this be the root cause? Plus, removing air intake ducting makes the popping much worse. Can that be ignition related?

[Coyote74]

Notorius for rotors burning through from underneath and shorting to cap or steel plate underneath rotor.

[enblethen]

My Banks kit came with a chip. I haven't had any problems with it.
I have changed spark plug wires several times as the back cylinder wires burn out.
I would suggest getting a new cap, rotor, plug wires and spark plugs. This is about all there is to a tune up.
Get the rotor and cap with the brass pins.

[352]

Start it up at night and look for sparks from the plug wires.

[Cousin_Eddy1]

Anyone know if the Banks kit comes with a "chip"? Cause if that chip richens up the FI mapping for the high flow exhaust, this would happen if it stopped working. I have no clue how or if the banks kit adjusts the fuel injection mapping. The Duchess had this already installed when i bought it 10 years ago.

[MountainAir05]

Check the distributor cap for arcing.

[polar76]

X2 replace the spark plug wires…
I had the same issue on a 94 Winny… with 454