Acceleration Noise

[RGx2]

I hear a noise from under the hood when accelerating that I can't pin point. It's not a knocking, grinding or metallic sound. More like a vacuum / exhaust leak, or maybe the engine is just bogging down upon acceleration.

Some background info: 1994 with 150K miles, 3.0 automatic. I just replaced the head gaskets, plugs, distributor cap and rotor. Lapped the valves (old school cheap). Compression now tests at 140 for five cylinders. The other cylinder is 130. Set the timing to 10 BTDC (spout out). Did a vacuum test on the intake manifold. The vacuum holds steady at idle (17.5) and at higher RPM (+21). No bouncing needle. No decrease in vacuum to suggest a plugged cat.

The truck starts VERY easy and seems to idle well. It also holds high speed well. I do not hear the noise during these times, only during acceleration. I also can't hear the noise with the hood up and revving the motor by hand.

The excelleration itself seems "almost" OK. Not great, but then it is the 3.slow motor. I will do the cable mod. However, I doubt the mod will effect the sound I'm hearing.

I can't find any exhaust or vacuum leaks. The air intake hose did have a leak at the intake manifold. I fixed it with foil duct tape, so I will double check that again to see if its the problem.

Does any one have suggestions on what could be causing this noise? It only happens during acceleration, so I don't think its a vaccum or exhaust leak. Perhaps advancing the timimg a bit might help?

Thanks,

RGx2

 

[Original_Ranger84]

Sounds like either your air intake silencer is gone, kind of a whistle/whine?

 

[dbp]

Let it run and spray some carb/choke cleaner or some starting fluid around (obviously this can result in a fire). Guaranteed to find a leak if there is one.

Otherwise, fill the intake with smoke and see where it starts coming out.

 

[RGx2]

Original_Ranger84,

Its not a whine / whistle type of sound. Its much deeper. But, I will check out the air intake silencer.

dbp,

I've sprayed some starting fluid around the motor and didn't find a leak. I was a little nervous spraying it and probably didn't do a good job. Although, the vacuum test seemed to indicate there is not a leak.

 

[dbp]

Yeah I dunno what to tell you then, I mean you sound like you're pretty good with what you're doing. I work in a garage but I don't do a whole lot of engine work as we have 3 guys that do that. I do hang out with them a lot when I don't have anything to do and I know that if they couldn't find the leak the next step would be to fill it with smoke...just make sure wherever you put it in that it's sealed so it doesn't come back out there.

There's gotta be some creative ways to make smoke without a smoke machine though.

 

[spitse]

I don't want to hijack, but I think I have the same sound. It has a plugged sound from when in the cab. It only occurs 1/2 throttle or more. When driving, I loose power, bogs down. I popped the hood and accelerated the engine. I found it was coming from the air box, almost like a back fire or back pressure or something. Maybe a valve not closing all the way? I do have problems with #2 not working correctly/missing. I have a strong oder of fuel in the exhaust.

 

[Original_Ranger84]

I don't want to hijack, but I think I have the same sound. It has a plugged sound from when in the cab. It only occurs 1/2 throttle or more. When driving, I loose power, bogs down. I popped the hood and accelerated the engine. I found it was coming from the air box, almost like a back fire or back pressure or something. Maybe a valve not closing all the way? I do have problems with #2 not working correctly/missing. I have a strong oder of fuel in the exhaust.

To your question, it sounds like you are running really rich. The engine is spraying more fuel in the cylinder than it needs and at hig sppeds it just bogs down because it isn't able to completely burn the mixture and some of the power from the cylinders is lost. It would also smell strongly of fuel from the exhaust.

You have either a lack of air or you are getting too much fuel. I would check out the MAF sensor and get it cleaned up, And also look at your Air Filter to see if its clogged.

 

[comparini3000]

There's gotta be some creative ways to make smoke without a smoke machine though.

I'm getting the bank 1 and bank 2 lean codes and I'm looking into the possibility that it's a vacuum leak. I tried the propane idea but couldn't find anything, and after doing some more research, I heard the smoke technique would indicate leaks when propane might miss them.

So I got to thinking...and I want to make a crude smoke machine using dry ice and water. Does anyone know if that would cause any damage to my truck? I don't think it would, but then again, I don't know much.

If I end up giving it a try, would it be worth it to make a smoke machine thread for other people's reference? It might be too simple of a topic to make a thread on, but it's probably the only contribution I could make to these forums at this point.