This thing is about to drive me batty. Runs great till it warms up, then starts flooding. Can't seem to get enough air to it to clean it out. Just floods and dies. Let it cool for a while, and it's fine again.

Only code I get is 41, for O2 sensor says fuel system lean. Possibly bad sensor telling the computer to give it more fuel?? It sure as heck isn't lean.

The coolant temperature sensor is functioning properly, and has the requisite five volts to it.

The TPS is smooth, and in range.

Whacked the converters off this morning, in case I had a stoppage. No improvement. Now I just have a loud truck that floods.

'bout to pull my hair out, and there's not much left to pull. Anybody got any suggestions??

 

How do you know it's flooding? Usually flooding refers to dumping too much gas in via the carb on a cold motor. Never heard it referred to on a warm FI motor.

Swap the O2 sensor out, and see if that makes an improvement. Also check for vacuum leaks.

 

Sure acts like it's flooding. Sputters spits and stalls. Sometimes you can catch it before it goes. If you can ever get it wound back up you can save it, but you have to really feather the pedal to get it wound up, and then keep the rpm's high.

Fuel pressure is great. Stays around 50 psi.

Strong smell of gas when it's acting up. When it finally dies, the plugs are wet with gasoline.

 

The fuel pressure is actually a little low. It should be 55 to 60 psi, although I don't think that's the whole cause, just based on the plugs being wet with gas. Have you checked the coil or any of the other ignition parts? The vacuum advance maybe? When's the last time it had a tune-up? Just a couple ideas...

 

I dunno about a tuneup, but the plugs and wires are fairly new, and are clean. The spark is hot enough to jump out of the end of the boot, and grab my finger, as I painfully discovered. The timing is at ten degrees, with the spout removed. It really doesn't act like spark breakdown, but I have been wrong before.

I am usually quite adept at troubleshooting these systems, but I've got two here that are driving me nuts. This one is my neighbors, and I have a 302 that's giving me fits. but I'll get to that when I finish this one. One thing at a time.

I'm really stumped. Any suggestions would be greatly appreciated.

 

Try unplugging the O2 sensor and see what it does. If it continues to run well, then I'd say replace the O2 sensor. I thought maybe fuel pressure regulator diaphragm was busted, but that would make it run rich all of the time, not just when warm.

 

Update. I have now gotten to the point of throwing parts at it. The temperature sensor was open all the time, so I replaced it. Replaced the oxygen sensor, and threw in a TFI module for good measure. Checked the temperature sensor on the air intake. Had five volts to the sensor, and the sensor showed varying resistance, depending on the teperature of the engine at the time. Still have the same problem.

Anybody got any ideas????

 

Did that clear the O2 sensor code?

 

Did you unplug the battey ground to reset the computor, after you put in the new parts? What are the codes now? Are all the plugs wet? I was thinking a leaking injector, on that plug you pulled??? But I'm no expert.

 

If the plugs have been wet at any time, change them. If you were to take an ohm meter to a new plug vs the ones that have been wet, you'll find the plugs that have been wet have more resistance to them, and will produce less spark. Once an engine is flooded(for any reason) change the plugs and the oil at the same time. Oil tends to soak up the excess fuel, and will cause a new set of plugs to foul at the first firing. Clear the codes, as previously mentioned, by disconnecting the battery for about 10 minutes.(do the oil change and then reconnect to make sure)

 

Ok here's where I'm at with this. All the codes are cleared, except the usual 32, egr not controlling code. The map sensor, oxygen sensor, fuel pressure regulator, and tfi module have been replaced.

No more codes, all gone.

Still have the problem. It will run good for the first little while, and then it starts breaking down. Can't seem to get enough air to it to make it run right.

I thought leaking injector, but it should still run on the other five. not just quit altogether. Made a dump run in it this morning. And almost made it home before it started missing. I got the rpms up and kept on coming, but in the end I couldn't save it. I started losing cylinders, one by one, till it shut down completely. Waited about 15 minutes, started it up and came on home, albeit sputtering and muttering all the way.

Sounds almost like the spark is breaking down now, eh?

Maybe RR4E is right? Plugs look good, but maybe they are shot?

Any opinions?

 

Try pulling the throttle body off the intake and check for a bad gasket. The 4.9 will suck the gasket apart and cause some strange things. Also, try disconnecting the vacuum line at the EGR and see how it runs. It could have a bad vacuum control valve.

Unplug the water temp. sensor and let it run in the closed loop. This will tell you if it is related to the ECM and it's various sensors that give input only when the engine is warm.

Have you checked the coil for breaking down? Look in the end to see if it is burnt from jumping fire. Try a known good one on it.

Or, it could be a bad ECM. The 94-95 t-birds have had some problems with ECM's that will go bad and hold the injectors open, so it could happen with these engines also. I think I read in these forums where someone else had some strange things going on with his 4.9 that turned out to be the ECM.

I hope one of these things helps.

 

The plugs are recent, but have been flooded several times now, and likely at about 30% or less of initial efficiency. They're a cheap change, along with the oil. I do stress the oil change as well, as any flooded engine pumps the oil full of gasoline...one backfire and the truck is up in flames!

The warm running problem could be caused by several things. Choke(if carbed) or enrichment sensor(fuel inject) not operating proplerly. With no codes showing, it's likely to be something simple, and likely over-looked. I'd make sure the cap/rotor, and wires and plugs are in good shape first. Re-check your timing, and check for a slipped outside ring on your harmonic balancer. One thing to check on the plugs is that they are touqued in. Many consider this to be not important. When I install plugs, I put engine oil on the threads(careful not to get any on the elctrodes) and thread them in hand tight, then tourque them to 10ft/lbs(cast head) or 12 ft/lbs(aluminum head). You can take this one step further by purchasing index washers, and making a mark on the side of the plug with a felt marker, and changing index washers until tourque is achieved by having the electrode gap facing the intake valve, which, in theory, provides the most available spark to the incoming fuel/air mixture. I went this way with a previous truck for fuel mileage only, although it only saved me roughly a 2% increase on the over-all, and wasn't really worth the time it took. It would be worth it if you were drag racing and looking for every available ounce of hp out of your engine.
Proper touque, on the other hand. I've found various engines over the years as a professional motorcycle mechanic, that suffered greatly, and mostly flooded, due to improper tightening of the plugs. The engine oil allows the threads not to bind with the dis-similar metal of the heads(steel vs cast or vs aluminum) and provides a true tourque factor, thus allowing for true compression ratio and sealing of the cylinder. Give that a try, and see what happens. Might sound silly, but it might also be the answer you're looking for.

 

New plugs, new oil, same problem. Have good vacuum at the manifold. I disconnected the egr valve before I ever even started this whole scenario. Now what???

Am I down to the ecm yet?

Any ideas????

 

Try the MAP sensor, located on the passenger firewall. I never even thought about that earlier. It will control the amount of fuel entering the engine.

Try a good coil.

Unplug the coolant temp sensor to the ECM so it can run on the preset paramaters and see what happens.

It appears to be temperature related, if it runs good cold. If it just runs OK cold, and gets worse as it warms up, then it could be other things, like the throttle body gasket.

Be sure and check the throttle body gasket anyway. There are only 4 bolts, and takes about 5-10 minutes to do. Everyone I know who has the 4.9 has had their gasket come apart at sometime.