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Old 07-28-2014, 08:39 PM   #1
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Cool Location of Electronic Control Module (ECM)

Hi--just joined the forum hoping I can connect with a knowledgable person who would know the location of the Engine Control Module (ECM) on my RV. It is a 1997 Rexair model 3200. I'm having a problem with the engine missing when placed under load. My mechanic has eliminated other potential causes and has zeroed in on the ECM. I would like to remove the existing one to verify its part number, etc. Any suggestions would be appreciated.
-rudyblue
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Old 07-28-2014, 08:48 PM   #2
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Unfortunately going to need more info to be any real help .
Chassis manufacturer ? Engine manufacturer ? Gas ? Diesel ?
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Old 07-29-2014, 02:56 AM   #3
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Cool Location of Electronic Control Module (ECM)

Of course you are correct that info is required. The vehicle has a Ford F-Sup Duty chassis, 1996 vintage, gas with a 460 engine.
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Old 07-29-2014, 09:03 AM   #4
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rudyblue,
There are others on these forums that know a lot more specific information concerning your Ford 460 engine but in a general way I can tell you this.

I don't know your mechanic or his/her quality of work but I learned a long, long time ago just because someone said, "Well I checked everything and all checks out OK so I think it's this." That's a sure way of spending a lot of time and $$$ chasing your tail. Often times I would end up finding something wrong with an item that was said to be good or had already been replaced and it was defective.

That said, Usually when an engine misses under load it means that under normal or slight load all electronics/electrical connections and parts operate just fine but when high demand is expected things break down. This happens because when under load cylinder head pressures rise and it requires the ignition system to increase its power output and things break down.

Here's where it gets a little fuzzy for me because I don't know what the 1997 engine has.

Regular engines for that time period had plug wires, a coil, cap, and rotor. A few years later they switched to a coil for each cylinder or COP (Coil Over Plug) therefore no plug wires cap or rotor. So you can see how diagnosis gets confusing. If the 460 engine is of the older variety this is important.
You said that your mechanic, "Eliminated possible causes." Does that mean that he changed the plugs, wires, cap, rotor, coil???? All these items (if your engine has them) will perform well until under load.

Even if he/she changed them that does not mean that all are working correctly.

I started working on ECM controlled engines of all varieties in 1979 and did until I retired from teaching in 2006. In all those years I only changed ONE ECM and I'm not sure that one was bad. I'm not saying that it's not entirely possible but I'd look other places first. To be fair I taught a lot more than just ignition systems so I didn't work on them every day. Those that do probably experience many more bad ECMs than I did.

My educated gut feeling is you are having a high voltage breakdown somewhere in the secondary ignition system. The energy (high voltage spark) to one or more cylinders is leaking out of a defective plug wire, spark plug boot, inside a cap or somewhere and it's not getting to the plug gap.

Others with more specific knowledge of your 460 engine will chime in soon.
Do let us know what you eventually determine is the cause.

TeJay
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Old 07-29-2014, 12:41 PM   #5
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Your ECU is to be found mounted on the firewall either directly in front of the steering column, or just to the left of it. However i agree with TeJay, it's unlikely to be at fault.

If you post the things your mechanic HAS tried, you may get more suggestions. Mine would be for you to ensure your mechanic understands that this ECU is Ford's OBD-1 system, and so it performs diagnostics all the time, and can read them out to a Ford specific code scanner. So probably the ECU already knows what is wrong, you just have to ask it. Do not let anyone tell you that if you have no Check Engine light, then you need not scan for codes. That is NOT true for this system.
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Old 07-29-2014, 03:56 PM   #6
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As mentioned above the PCM (ECM) is usually mounted on the left side of the steering column. But as others have said I highly doubt that the PCM is the issue based on the description provided. When you have an engine miss under load that pretty much points out to 2 things, spark and fuel. If pressure is low under load you will lean out and will have a lack of power. A fuel pressure gauge must be put on the fuel rail and pressure tested under full engine load when driving. You want to see over 35 PSI. Spark would be the next suspect. Coils were known to break down. Plugs, wires, cap/rotor would be the next suspect. Have they all been replaced with new high quality parts? Any exhaust manifold leaks? possible burned exhaust valve could be causing an issue. A PCM does not see any engine load. It just takes low voltage low amperage signals, calculates them, and then sends out the proper outputs. Fuel injectors are controlled via the PCM on the ground side. So it is a slight possibility that the injector transistors could be going bad but even more likely is a PCM ground issue (wiring). EEC IV systems do not provide misfire monitoring so you will not get any misfire codes. So it becomes old school diag by pretty much replacing first suspect parts. I cannot tell you how many PCMs I replaced from independent shops saying they were bad but I can tell you none of them fixed the issues. However I can count on one hand how many PCMs I did need to replaced over a 20 stretch as a Ford technician. At the dealer I used to work at we had a guy that we nick named "baby carriage". This is because we would not trust him to fix a baby carriage. He was also known as the PCM king because if he couldn't fix the problem in a few minutes he ordered a PCM. I can only seem to remember 2 that actually fixed the issue.
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Old 07-29-2014, 08:10 PM   #7
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Cool Location of Electronic Control Module (ECM)

Thanks to TeJay, mpaton & Jamesrxx951 for your prompt prompt and knowledgeable responses to my question. I learned a lot and thought perhaps I should give you the details of my vehicle problem that prompted my question to this forum. The following is the report written by the technician that analyzed my RV's problem. His conclusion was that the PCM was suspect and should be changed.


Tech notes: Road Test and verified erratic miss under load. Inspected & found Cap & Rotor in poor condition. Replaced both and recheck resulted in no change.
Performed scope check and found ignition secondary OK.
Installed fuel pressure gauge & TD(?) normal. Performed injector service--no change.
Installed NGS & EEC (Electronic Engine Control?) check pass/pass.
Road test vehicle while monitoring several different Parameter IDs (PIDs). It was noted that the system goes to open-loop even under light load or when put in gear (anytime Manifold Absolute Pressure (MAP) PID goes above 103 hz.

I would be very interested to hear your opinions on his conclusions and if you think he missed anything. The price they quoted me was a bit rich for our budget and so I hoped it was a task I could perform myself. Hence my original question. I did find a replacement part on the internet price at $140.

Thanks again to all of you for sharing your knowledge.
-Rudyblue
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Old 07-29-2014, 09:10 PM   #8
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I don't remember if under accel or under what throttle position the PCM will go into open loop. However if it was me I would replace the plugs and wires and maybe the coil before anything else. I would like to know what the fuel pressure was at under a full load acceleration since plugged fuel pump screens are not uncommon. Again not saying the PCM is not bad it just takes a lot of convincing that it is bad.

Plus just the age of the coach would warrant replacement of the coil, wires, and plugs. Rockauto.com sells motorcraft coils for $35, Motorcraft wires for $37, and motorcraft plugs for $2.37 each. Seems like some pretty killer prices to me.
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Old 07-29-2014, 09:14 PM   #9
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Glad you're aboard. I see you have some of the best working on your query. Best of luck in finding a solution. When you get it figured out enjoy your adventures and be safe.
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Old 07-29-2014, 09:33 PM   #10
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Not for nothing, I had a gas coach miss only when climbing a long hill. After replacing all plugs,wires,coil,Fuel filter,once stopped for gas right after climbing a long grade, I heard a whoosh when I removed the gas cap, Eureka.New gas cap, no more missing.
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Old 07-30-2014, 04:51 AM   #11
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Quote:
Originally Posted by rudyblue View Post
Thanks to TeJay, mpaton & Jamesrxx951 for your prompt prompt and knowledgeable responses to my question. I learned a lot and thought perhaps I should give you the details of my vehicle problem that prompted my question to this forum. The following is the report written by the technician that analyzed my RV's problem. His conclusion was that the PCM was suspect and should be changed.
Than you very much for doing this; the forum doesn't often see useful and informative feedback like this. I will say that your technician seems more informed than I had expected. I'll defer to James on some of this, as he's more current on Ford tools and practice than I am. However I'll say in passing that some misses under load have involved the torque converter unlocking and locking again. That would be light load however.


Quote:
Originally Posted by rudyblue View Post
Tech notes: Road Test and verified erratic miss under load. Inspected & found Cap & Rotor in poor condition. Replaced both and recheck resulted in no change.
Performed scope check and found ignition secondary OK.
Installed fuel pressure gauge & TD(?) normal.
This is useful, although as James says, knowing the fuel pressure under full throttle would be more useful (should be 39psig)
Quote:
Originally Posted by rudyblue View Post
Installed NGS & EEC (Electronic Engine Control?) check pass/pass.
NGS is a Ford shop tool I believe, James can fill us in. It's good that he has one. It would be better to confirm that there were no CM (Continuously Monitored) codes, and that the KOEO and KOER tests all passed.
Quote:
Originally Posted by rudyblue View Post
Road test vehicle while monitoring several different Parameter IDs (PIDs). It was noted that the system goes to open-loop even under light load or when put in gear (anytime Manifold Absolute Pressure (MAP) PID goes above 103 hz.
This is looking like quite a thorough test, and I have useful information here. It is only what I have been saying here for years to the disbelief of many. That is that there is no useful driving condition in which a 94 or later 460 engined chassis will enter closed loop control.
This is not conventional wisdom, but it applies here. I know this because I have extracted the ECU code and made sense of it, and I now can see just how Ford intentionally disabled Closed Loop Fuel Control. You might enter closed loop at very light throttle on a slight downhill.

So your tech finds this noteworthy, but it is entirely to be expected.

It has side effects, mostly that the ECU cannot compensate for ethanol in the fuel, which I would guess you are using (it's hard not to). This makes the engine run leaner than intended and will make a lean miss happen sooner.

I this $140 fairly reasonable for an ECU these days. I hope it is one for an RV. I am guessing that your ECU will have a code of "BOX0" on the 60 pin connector, in a font 3 times bigger than all the other characters. This ECU also controls your transmission, and you really want the correct one, not one from a pickup that someone says will do.
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Old 07-30-2014, 07:15 AM   #12
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Working with other Ford Forums we are seeing PCM starting to fail and the age right now seems to be 1994 and older PCM Computers.

But it does not sound like yours is failing as that is not what we are seeing. Most of the time when the PCM Computer fails is because the clock has stopped running in them. Some times the clock will restart for a short time and sometimes not.
When the clock stops the fuel pump will run all the time the key is on with the engine not running and the fuel injectors will not be grounded (firing) while cranking.
You can fix the PCM Computer most of the time by replacing the electrolytic capacitors that are bulging or leaking and bridging any gaps in traces that are ate through by the acid leaking out of the electrolytic capacitors. Sometimes a radio repair shop can do this and not charge much.

So I would say if you think it is bad open it up and and look at the board for any electrolytic capacitors bulging or leaking and any burnt parts on the board. If you do not see anything wrong it is more than likely still a good PCM Computer.
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Old 07-30-2014, 07:21 AM   #13
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missing under load

I also had 1996 460 that would miss under load or hard acceleration and it was the control module . Mine was located behind and to the right of the brake booster
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Old 07-30-2014, 08:02 AM   #14
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Quote:
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I also had 1996 460 that would miss under load or hard acceleration and it was the control module . Mine was located behind and to the right of the brake booster
When replacing the ICM (Ignition Control Module) on 1994 - 1997 F53's make sure the ICM is Black in color. The engine will start with the Gray one but it will not run that well as you will have poorer MPG and less power.

Note that most auto part stores and some Ford dealers will try to sell you the wrong Gray ICM as the listing is wrong in their computers.
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