Hello AllThis is probably a question better asked on Car Talk using engine noise vocalization, but I'll give it a try here. I don't have much that is solid to go on, so please bear with me.I have a 1989 Class C built on a Ford E350 with the 460 engine and 45k miles. I was powering up a moderate hill the other day and the exhaust noise/engine noise suddenly drastically increased. I thought at first that the transmission had downshifted but it had not. Pulled over, checked all fluids and all was fine. Engine was running great, transmission seemed fine, and I could not replicate the noise in neutral.On the subsequent drive home and on all test drives since the noise returns when the engine comes under load while climbing a hill and sometimes when accelerating on the flats. I will step on the gas, the engine noise will be normal, and then about 2 seconds later the increased engine/exhaust noise commences. It *only* happens when the engine is under load.It sounds like it is on the passenger side. I removed the engine cowling and poked around. Noticed that the rearmost exhaust manifold bolt on the passenger side was sheared off. When driving around the neighborhood I can replicate the noise, but it doesn't obviously come from the exhaust manifold. It seems to come from further back along the exhaust pipes, but I've been unable to see or feel any cracks or loose fittings.I am baffled, and I'm hoping that someone has stumbled across this before and can point me in the right direction.Best,Jim

Are you sure it wasn't just the cooling fan (clutch fan) engaging? They are necessarily very loud when they do so.Get the manifold fixed asap otherwise it will do more damage.

Roger re the manifold fix. I intend to install headers (recommendations would be welcome!), but only once I convince myself that the noise isn't the symptom of a much more expensive problem.Best,Jim

Thats really the only noise I can think of that would come and go - and it is a very loud engine type when it happens.

Your cat could be failing too. If I recall those model years had iffy cats and Ford was replacing them. I believe the guts were coming loose in them )if memory serves).

I'll investigate the clutch fan. Will have to do some poking around to get smart on it. Does it make sense that it would only engage under load?I like the cat idea, but any thoughts on why it would manifest itself only when the engine is under load? I'd have thought I could replicate that problem in the driveway. Maybe there is some flex due to engine torque that is causing something in the cat to loosen up?J

Exhaust noise(?) under load: 1989 Class C E350 7.5L

12 Replies

atmjah
Explorer
Sep 06, 2013
Hello All

Turns out it was not the exhaust manifold and was not the fan clutch (I did, however, fix the sheared bolt on the manifold).

The cause of the noise was a component of the emissions control system whose function I have yet to determine. There are two approx 1" pipes that come from the cat converter (one from the front, one from the back) wrap around the side of the engine and then disappear into the difficult-to-access passenger-side front of the engine. For most of their run they are metal, but for an approx 8" stretch as they transition from under the car into the space occupied by the engine (right next to the exhaust manifold!) they transition to hose. One of those hoses blew out and that was where the noise was coming from. I replaced the hose, but first trip out when I went up a hill the power started to drop, the hose burst again, and the noise returned.

The purpose of the pipes is not described in either book I have on the car. It is *not* one of those systems that injects air back into the exhaust manifold at each exhaust port. I will open another thread to ask for help identifying.

Best,
Jim
DaCrema
Explorer
Jul 10, 2013
A crack or break in the exhaust system would make that noise. Just driving around the back pressure is not enough to make a noticeable difference in sound. Under load the back pressure is increased and you are hearing unruffled exhaust. If you put a gloved hand over the tail pipe opening, you should hear the leak (and with help be able to find it) - if that is the issue. If there is no leak you will not hear a change, and the pressure will want to push your hand away. Don't leave the pipe blocked long. This is a two person test, that is do not block the pipe and then go looking for a leak. You will hurt the engine and/or cat.
atmjah
Explorer
Jul 10, 2013
Thanks everyone. I'll get the manifold sorted out regardless.

I'm still scratching my head about how to test the fan clutch idea (I live in Monterey...it is *always* cloudy and cool!), but the curious thing is that I've had the RV for almost a year and this is the first time the noise has occurred.

I agree that the 2 second delay makes the manifold idea problematic, and I still don't see why it would only happen under load. I picked up a tach to see if there is any RPM change associated with the noise. Would have an answer for you all already but learned this morning that the coil has a fancy plug rather than screw-on terminals!

Best,
Jim
PaulJ2
Explorer
Jul 09, 2013
Its the fan clutch engaging. Exhaust noise would be instant no 2 second delay.
Take it for a drive on a cool morning/day to prove it.
bsinmich
Explorer
Jul 08, 2013
We had the same in a '89 in Jamboree. We had 2 convertors in the few years we had it. The first 2 times we had skipped Church to get on the road and got stranded & towed. I had the convertor off and happened to drop a big pipe through it. I never had a problem again. We didn't need exhaust testing then or now. I had a bolt break off on the exhaust manifold and that is the noise you get. My mechanic had a fellow with a portable EDM machine come and remove the stud in the head. That meant no removal of the head and was only $50-60 at that time (1990).
super_camper
Explorer
Jul 08, 2013
atmjah wrote:
Hello All

This is probably a question better asked on Car Talk using engine noise vocalization, but I'll give it a try here. I don't have much that is solid to go on, so please bear with me.

I have a 1989 Class C built on a Ford E350 with the 460 engine and 45k miles. I was powering up a moderate hill the other day and the exhaust noise/engine noise suddenly drastically increased. I thought at first that the transmission had downshifted but it had not. Pulled over, checked all fluids and all was fine. Engine was running great, transmission seemed fine, and I could not replicate the noise in neutral.

On the subsequent drive home and on all test drives since the noise returns when the engine comes under load while climbing a hill and sometimes when accelerating on the flats. I will step on the gas, the engine noise will be normal, and then about 2 seconds later the increased engine/exhaust noise commences. It *only* happens when the engine is under load.

It sounds like it is on the passenger side. I removed the engine cowling and poked around. Noticed that the rearmost exhaust manifold bolt on the passenger side was sheared off. When driving around the neighborhood I can replicate the noise, but it doesn't obviously come from the exhaust manifold. It seems to come from further back along the exhaust pipes, but I've been unable to see or feel any cracks or loose fittings.

I am baffled, and I'm hoping that someone has stumbled across this before and can point me in the right direction.

Best,
Jim

I am experiencing a similar problem, its the manifold.
j-d
Explorer II
Jul 08, 2013
We had a Class C on a 1983 E350 with the 460. On a hot day, running along the level interstate using cruise control, the FAN would kick in as we climbed the gradual grades for overpasses. It would build quickly to an exhaust-like sound then fade away again when we reached level ground. First time I thought we were being passed by a motorcycle gang.
We also had exhaust manifold leaks. In our case, the stamped steel gaskets rusted out and the manifolds warped. I was fortunate to get every fastener out. Both sides, 8 each, all 16. In our case, I had the manifolds re-surfaced and put them back with new stamped gaskets and new bolts.
atmjah
Explorer
Jul 08, 2013
I'll investigate the clutch fan. Will have to do some poking around to get smart on it. Does it make sense that it would only engage under load?

I like the cat idea, but any thoughts on why it would manifest itself only when the engine is under load? I'd have thought I could replicate that problem in the driveway. Maybe there is some flex due to engine torque that is causing something in the cat to loosen up?

J
Dakzuki
Explorer II
Jul 08, 2013
Your cat could be failing too. If I recall those model years had iffy cats and Ford was replacing them. I believe the guts were coming loose in them )if memory serves).
ScottG
Nomad
Jul 08, 2013
Thats really the only noise I can think of that would come and go - and it is a very loud engine type when it happens.