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Discussion Starter #1
Hi guys,

Vehicle is a 1993 E350 motorhome, 7.5L gas with automatic transmission, approximately 80k miles.

The problem is an intermittent (but fairly reproducible) hollow rattling/chattering sound, accompanied by a loss of power to the wheels. The noise appears to be coming from the engine area (forward of the driver's seat).

This happens primarily in third gear, and sometimes in OD, especially after coasting and then lightly accelerating (feathering the pedal). It happens anywhere from 30-60 mph.

If I press harder on the gas, the noise grows, and there is still reduced power. When I pull my foot off the accelerator and push it harder, it operates normally (even without downshifting).

I took this to a truck shop, who said the noise was coming from a rotted exhaust heat shield. They didn't think they'd be able to find a replacement, so they put a clamp on it to tighten that down. The noise is less since they did that, but that was obviously a side effect symptom of all this vibration.

I plan to bring it to a Ford truck dealer. I'd love to hear ideas before I go and get taken for something silly.

Thanks in advance.

Mike
 

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First I would want to ask when did it start? Is it new, or been coming up for a bit now? Just some thoughts... Sloppy timing chain. .. If its too loose, it could be slapping around, and changing your timing. .... Did this just start? Maybe a tank of bad fuel causing the engine to ping under load? Some fords of that era used a knock sensor... not sure if the 460 was one of them... but if it starts pinging it will back the timing back till it stops... that will make you loose power. And really... if it WAS the heat sheld... depending on where, how, and what its hitting it COULD had triggered the knock sensor.... [ maybe a reach... but possible..] Another thought... if it depends on on throttle angle... Maybe the TPS going south, and throwing strange voltage readings to the PCM.. That being said, the first thing the dealer is going to want to do is make sure the tune up has been done.. Plugs wires, cap, rotors... Any time you have a strange reduced power issue thats the first step.
 

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Discussion Starter #3
I first noticed the noise last summer. I didn't really pay attention to the power loss until I really started trying to pinpoint the symptoms after the shop couldn't make the noise stop. I would always just lay off the gas when the noise started.

Seems odd that it really only does it in gear, especially third gear. I can't get it to happen in park.

Mike
 

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Thats why im leaning toward timing issue... It would only act up under a load, not a free rev. if it was me, I would start first making sure the tune up is up to date... cap rotor wires, plugs, filters etc... then I would check for slop in the timing chain next... [ you can check that buy watching the dist rotor, wile you turn the crank back and forth and see if there is a delay in moving.] if that all checked out, I would go deeper in diag.. but thats a nice easy basic starting point.
 

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Discussion Starter #5
Wow, makes sense. The whole time I've been fearing a tranny problem. Can't recall if this engine is electronic ignition vs distributor. I've owned it 15 years, and have always had it serviced by others. I've done plenty of work on my daily driver cars and trucks, but have usually shyed away from the RV.

I do occasionally get a CEL light as well, maybe I'll start with getting that read. That's also even more intermittent than the power/noise problem.

Another odd thing that it's done for the past year or more (and no shop has resolved) is that the CEL light is always on, dimly, when the engine is running. Really can't see it during the day, but it's very noticeable at night. It shines brightly at startup, and rarely (as mentioned above) at other times.

Mike
 

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Wow, makes sense. The whole time I've been fearing a tranny problem. Can't recall if this engine is electronic ignition vs distributor. I've owned it 15 years, and have always had it serviced by others. I've done plenty of work on my daily driver cars and trucks, but have usually shyed away from the RV.

I do occasionally get a CEL light as well, maybe I'll start with getting that read. That's also even more intermittent than the power/noise problem.

Another odd thing that it's done for the past year or more (and no shop has resolved) is that the CEL light is always on, dimly, when the engine is running. Really can't see it during the day, but it's very noticeable at night. It shines brightly at startup, and rarely (as mentioned above) at other times.

Mike
Ive never heard of a CEL flickering... thats a new one.. But ya, check for any codes first. Really whenever your working with these kinds of issues, you really need to start with the low hanging fruit. Other things might not be the main cause of a issue.... but some times a lot of small things wrong, can stack up and cause a bigger issue.. like the heat sheld... odds are was not causing the issue.... but the noise was something you heard when it was acting up.. Wherein the noise you figured was part of the issue... was really just something that came up during that time...

those trucks do have a dist.. they are electronic ignition, and EFI.. but still uses a Dist and cap, rotor and plug wires. Its pretty much just a old school 460 big block, with modern controls. As for tranny.... well there is always a chance... but thats not really they way they normally fail. Does the trans you have have a OD button you can push on the shifter to kick it in and out of OD? They used a few different setups in that era. Being you have that odd CEL light flickering.. maybe get in there and pull, and clean up all the electrical grounds. Maybe a bad ground or two are causing the PCM to do some strange things to the engine/trans management.
 

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Discussion Starter #7
Yes, it has a push button OD switch on the shift lever. The light stopped working on it last year, but the switch functions. I'm planning to replace that after I get the rest sorted.

The CEL doesn't flicker, it stays on dimly. There are occasions that it comes on brightly, which I assume means it's throwing a code.

Mike
 

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Discussion Starter #8
BTW, I've done some research on the dim CEL problem. Apparently, the CEL always has power when the key is on. The computer allows a ground when a code is set, to complete the circuit and light the CEL.

I guess the trick is to see where the short is.

I've read another theory that it could be caused by a dirty board on the back of the instrument cluster. Aside from having to pull the dash, that would be easier for me to DIY than chasing a rogue (bad) ground.

Mike
 

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Discussion Starter #11
I'll take a look at those, thanks.

Haven't had time to do anything but think about it...

Before I bring it anywhere, I'll clean the instrument cluster and have AutoZone read the codes. They're useless for advice, but at least I'll know if there are numbers. Of course, I'm sure they'll tell me they can't read an RV, or something so old, or both...

I can replace just about anything myself, but don't want to deal with setting timing.

Mike
 

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I'll take a look at those, thanks.

Haven't had time to do anything but think about it...

Before I bring it anywhere, I'll clean the instrument cluster and have AutoZone read the codes. They're useless for advice, but at least I'll know if there are numbers. Of course, I'm sure they'll tell me they can't read an RV, or something so old, or both...

I can replace just about anything myself, but don't want to deal with setting timing.

Mike

Well you need to read codes... Problem is a 93 Ford ois not OBD2. I doupt a place like AutoZone can read them.. The good news is there are ways to read them yourself.. Here is one thing I found on a quick search.. there are other ways to read them also..
Ford OBD I Diagnostic Trouble Codes¦ Retrieve and Repair
 

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mass air flow sensor. they make a cleaner for it. do not use anything else
plus the pvc hose. change it

john

Im not sure if it does have a MAF sensor. Im not 100% sure on the big block... But I believe just the later years [95 or so... ] and maybe a year or two before for Cali, and HO engines...
 

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Discussion Starter #14 (Edited)
Thanks Paul. I had a 94 Explorer, and bought an ODBI reader for it, might still have that in the garage. I remember using a paperclip or wire on that too, as well as GM cars from the 80s.

Calling that old Actron unit a "reader" is a stretch: it didn't even have a display screen. But, it did have some control buttons (was easier than the wire), and would beep when the light was on (you could count beeps). Here's a pic I found online.

Mike
 

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I have read about some Ford automatic overdrives having a "shudder" in high gear around 40 mph when it goes to shift into overdrive,or the lock up torque converter locks in...
Some mechanics swear "Lube Guard" additive cured this issue,one who I know that services the police cruisers said many of the Crown Vics they had did that after they hit 50,000 miles or so,and the additive cleared up the problem..I guess it frees up a sticky valve in the valve body that operates the lock up torque converter ..
 

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Discussion Starter #16
I started it up tonight for a few minutes. Now that I'm paying more attention, it was definitely running roughly at startup. Something is definitely going on with the engine, I'll get that cleared up before chasing the tranny.

Mike
 

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Discussion Starter #17
Got it back from the shop yesterday. Had them do a full tune-up (plugs, wires, cap, rotor) and tranny service (fluid and filter) and engine battery.

They're saying it's the transmission. After this work, the symptom is still there, just much less vibration and noise (so far).

Knowing that I'm getting a dim CEL makes the PCM suspect, so I'm going to replace that and the TPS. Parts are ordered, hoping they'll be here on Monday so I can get it done Monday night after work.

If that doesn't fix it, I'm probably going to try a Ford truck dealer for a second opinion before dropping $3K on a guess.

Mike
 

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I'm not sure how handy you are, but that transmission should be very easy to replace. I'm pretty familiar with Ford trucks, the big block has its own bolt pattern that is different from the small blocks, but if you find a good used transmission from a junkyard or something, it's a weekend job to swap it if you are good at turning wrenches.

Also I would not take it to a Ford dealer. It's just a little too old and most if not all of the techs won't be any more familiar with it than a corner garage would be. They will just charge you a lot more money for parts and labor.

I'd take it to a good transmission shop. Ask around and see if someone can recommend a good shop. That transmission shouldn't cost more than $1000 or so to rebuild if you can remove and reinstall it yourself.
 
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