Understanding ECM / PCM
 

https://cimg5.ibsrv.net/gimg/www.for...ee9f81296e.jpg
https://cimg1.ibsrv.net/gimg/www.for...894e5171d1.jpg
https://cimg2.ibsrv.net/gimg/www.for...d508b34038.jpg
Hi Guys,

1990 Ford Club Wagon 5.8L 36K orginal miles

I have been having idiling issues that I can not get a handle on, the van will buck and stumble when first started up but seem to run fine when at highway speeds after warming up, it will also hesitate when at a stop. I have had to bump up the base timing to 14* just to get it run halfway decent when warm.

After reserching many threads I have found that some have had issues with the ECM. ( some say PCM ) and I do not understand the difference or what is actually in my van . I pulled it out today and took pictures hoping to see 3 capacitors that seem to fail in them but my unit only has one and from what I can tell it looks good. I am not sure if my unit has already been re-manufactured or not because it does not look like any other pictures I see posted on the web, but there is no labels or stickers from a separate company that would indicate it was.

My questions are :

1) What is the difference from a ECM and a PCM ?
2) What do I have in my van ?
3) Even tho the capacitor does look good and does not appear to be leaking , is there any other component in there that might fail causing rough idle ?

Any help appreciated, This is a wheelchair van and needs to be reliable...

More information on my problems with this van :

Nothing really that is two different names for the same thing. Technically ECM is engine control module and PCM is powertrain control module, the former only controls the engine while the latter controls both engine and trans but that is splitting hairs these days.
See above.
No your PCM looks great so I doubt it is causing your problem. Those plug wires are shot however and were very likely misfiring to the engine block so you need a new set. Get a new set from Ford that are designed to fit correctly and make sure the heat shields(if still present) are not gouging them, if they are rusted and/or bent out of shape remove them completely.

Good catch on the typo , I edited my original post to reflect my mistake. It is a 1990 with a 5.8L :)

No your PCM looks great so I doubt it is causing your problem. Those plug wires are shot however and were very likely misfiring to the engine block so you need a new set. Get a new set from Ford that are designed to fit correctly and make sure the heat shields(if still present) are not gouging them, if they are rusted and/or bent out of shape remove them completely.[/QUOTE]

Many Thanks for your quick reply.

The burnt wires in the video were the ones I replaced along with a new distribitor , plugs and ICM. Apparently the PO removed the OEM heat shield from the right bank and that is why when I put the new wires on I used the heat sleaves in the video. That being said , it appears that cylinder 3&4 are running hotter that 1&2 and I don't know why. ( witch is why I made that video and used it in another thread ) is it normal for them to do so ?

All that being said, I also replaced the coil in addition to the above mention parts but it has had no positive effect on my stumbling / ideling issue ( witch was present before I found the burnt wires and replaced everything )

The noise you hear when the engine is turned off (around the 5 min. mark in the video ) is puzzling to me and the best I can figure is that it is comming from the two square black plastic boxes mounted to the right of the coil but I am not 100% sure. Does anybody know what they are for ? ( they have vacume and electrical lines going to them )

I will put the ECM back in and make another video of the van running with the stumbling issue. ( witch is way worse when it is cold ) in the next couple of days to show you guys what I am up against.

As always any thoughts are appreciated.

Two things I think you should do..
1. check fuel pressure to see that it is stable and withing spec both with and without vacuum attached to the regulator(32-35psi with vacuum, 40-45psi without), and that is doesn't drop to zero immediately when the engine is shut off
2. Pull plugs and compare the color of the them on the hot cylinders compared to the others.

You could have some dirty injectors restricting fuel to those cylinders making them run lean... or they could be sticking open and dumping extra fuel in those holes.

The two black boxes beside the coil are the TAB and TAD solenoids, they control valves in the air injection system that supplies fresh air to the cats to help them burn off excess HC. You have the most complicated version with the spider manifolds on the side of the motor.. ford simplified the system in later models, and there will be a vacuum resovoir(juice can) somewhere under the hood that helps maintain a steady vacuum for this system. Those solenoids should not buzz like that so you may have one of a couple issues, could be an electrical problem making the solenoid rattle or it could be leaking air past the seal. Worth checking this out as it could be contributing to the engine operating issues, there should not be any air being injected upstream of the O2 sensor once the engine reaches operating temp, it should all be either sent downstream to the cats or vented to atmosphere.

My 1990 E150 4.9 6 cyl has the 3 symptoms indicating a bad IAC valve. I replace valve w no changes. I was reading about 30 year old ECMs and the problems they have. A new one is only 50 bucks after core at autozone so I'm going to replace it. I've looked in the FSM to find location of the ECM but still can't find it. Where is the ECM?

The ECM is on the passenger side under the blower motor, I had to pull the battery to remove the 10mm bolt that holds the wire harness on.

I was just there changing the heater core which thankfully was easy. Is the ECM outside of the pass compartment and in the "engine bay'?

The ECM actually sits in the passenger compartment under a black cover, but it passes threw the firewall to hook up to the wiring harness in the engine bay. The black cover snaps on the ECM , I cant remember if it slides straight back towards the passenger seat or straight down.

I can not find anything that looks like a juice can in the engine bay, I have found a plastic ball with one hose going to it that sits by the steering collume . Does this ball serve the purpose of the vacuum resovor or should I be looking somewhere else ?

Upon closer review, there is a round plastic thing just in front of the TAB and TAD that has two vaccume lines going to it, while the system is making that noise ( bleading down when turning the motor off ) I can effect a change in the pitch by moving it around. One of the vaccume lines is green witch I believe went to the EGR valve witch had been removed and blocked off with a plate. what is this round thing for and could my condition be related to a removed EGR valve ?

I can not get to the scrader valve on the fuel rail to get a gage on it to check the fuel pressure because Ford decided to put some metal tubing right above it , I have made an appointment with a local mechanic next week to get the pressure checked and fuel filter replaced, just in case all that stuff has to come off and report back.

That being said, when I pull the vaccume hose off the pressure regulator it makes no difference in the operation of the enginge at idle or at tacking out at 1400, so I replace it , the new regulator acts the same way. I know there is vaccume going to it at idle but it seems weak, How much vaccume should I see at the Fuel Pressure Regulator at idle ?

The plugs look the same on all cylinders half white and half black ( light gray / dark gray ) when looking straight down on them, ( no oil or carbon build up ) I have been running sea-foam and Berrymans threw the fuel system lately in case it is clogged injectors. I have never seen plugs look like this before and wonder if it is because of the sea-foam / berrymans . what are your thoughts on this ?

My 1990 E150 6yl C6 have a coffee can looking thing in a bracket under the floor just behind the pass seat.