At my wits end with my 04’ WJ Limited
07-26-2021, 11:48 AM
#34
CF Veteran
You can get a cheap OBDII scanner from Amazon for about $20 that links to your phone with bluetooth. I bought a more expensive one that works for all modules in the vehicles but still uses my phone
07-29-2021, 08:07 PM
#37
Junior Member
Thread Starter
I’m looking at another ecm now. I need to know will it work if it’s from the same year and engine (04’ Limited 4.7HO). They are they same part number except for the last letter…
Mine has a “D” at the end and the other one has a “B” at the end. The numbers are all the same except for the last number.
Mine has a “D” at the end and the other one has a “B” at the end. The numbers are all the same except for the last number.
07-30-2021, 08:08 AM
#38
Member
Ecm
I believe that will work. Last letter is a revision marker. (I have a ""collection " of ecm's). Sadly, all are 4.0 units. Good luck! R
07-30-2021, 09:20 PM
#39
Junior Member
Thread Starter
07-31-2021, 11:37 AM
#40
Old fart with a wrench
A DRBII or DRBIII diagnostic scan tool is like an Autel or Snap-on unit that allows you to run live function tests on different systems and get data output. They come at prices that range anywhere from $200 to $2000 and are designed for technicians for quick diagnosis of any vehicle with specific software for each make. Not only is owning one expensive, but constant updates need to be purchased. I didn't expect you to buy one, only to find somebody that has one and can run tests for you.
Shotgunning of parts can get expensive quickly. I've been there myself. I spent weeks replacing everything I could think of that could possibly be involved with my problem, only to find that one connector pin in one connector had the "greenies" and was making contact fine until it got wet or hot. How did I find it? A mechanic friend with a DRB scan tool.
The numbers on a PCM have to do with it's internal circuitry. The last letter has to do with it's specific programming for the options and equipment installed as well as any updates. I seriously doubt a PCM designed for a 4.0 will work for your 4.7 because the 4.0 uses waste spark ignition and your 4.7 has direct 8 cylinder outputs. The 4.0 only has 3 coils and fires 2 spark plugs every revolution, one on compression and one on exhaust. This was done to reduce emissions and the main reason for this engine's demise in later years. It just couldn't meet increasingly strict emission standards.
Shotgunning of parts can get expensive quickly. I've been there myself. I spent weeks replacing everything I could think of that could possibly be involved with my problem, only to find that one connector pin in one connector had the "greenies" and was making contact fine until it got wet or hot. How did I find it? A mechanic friend with a DRB scan tool.
The numbers on a PCM have to do with it's internal circuitry. The last letter has to do with it's specific programming for the options and equipment installed as well as any updates. I seriously doubt a PCM designed for a 4.0 will work for your 4.7 because the 4.0 uses waste spark ignition and your 4.7 has direct 8 cylinder outputs. The 4.0 only has 3 coils and fires 2 spark plugs every revolution, one on compression and one on exhaust. This was done to reduce emissions and the main reason for this engine's demise in later years. It just couldn't meet increasingly strict emission standards.
Last edited by dave1123; 07-31-2021 at 12:07 PM.
08-01-2021, 09:47 PM
#41
Junior Member
Thread Starter
Thank for the clarification on the scanner.
I have an ecm from an 04’ limited 4.7HO coming this week (along with a skim and the key).
I will update once I get it installed and figure out what’s going on.
I have an ecm from an 04’ limited 4.7HO coming this week (along with a skim and the key).
I will update once I get it installed and figure out what’s going on.
08-03-2021, 10:20 AM
#42
Old fart with a wrench
I just hate to see you trash a mechanically sound 4.7 because of electrical problems. I only latched on to the capacitors because they are something that most people don't think about and something that gets funky over time and are temperature related.
Their function is to absorb the primary backlash current produced when the ignition coils magnetic field collapses to create the high voltage spark. On the old breaker-point ignition systems, there is one inside the distributor cap that protects the breaker points from burning and pitting caused by this same current. The engine will not run without this capacitor.
Back in the early 60s, my friend and I experimented with transistorized ignition systems. At this time, the only transistors that would carry the load required were the size of a nickel and mounted on an aluminum plate with 2 screws. We kept burning them out until we put a diode in the circuit to stop this backsurge. When we finally got one to work, a set of breaker points would last 50K miles and still not pit. However, by that time there were commercially available systems that did the same thing so our experimentation didn't go anywhere except to impress our high school Physics teacher. Besides that, we were using an article in Popular Science Magazine that suggested it could be done.
So, you see, I'm an old fart with a wrench that's been around a long time.
Their function is to absorb the primary backlash current produced when the ignition coils magnetic field collapses to create the high voltage spark. On the old breaker-point ignition systems, there is one inside the distributor cap that protects the breaker points from burning and pitting caused by this same current. The engine will not run without this capacitor.
Back in the early 60s, my friend and I experimented with transistorized ignition systems. At this time, the only transistors that would carry the load required were the size of a nickel and mounted on an aluminum plate with 2 screws. We kept burning them out until we put a diode in the circuit to stop this backsurge. When we finally got one to work, a set of breaker points would last 50K miles and still not pit. However, by that time there were commercially available systems that did the same thing so our experimentation didn't go anywhere except to impress our high school Physics teacher. Besides that, we were using an article in Popular Science Magazine that suggested it could be done.
So, you see, I'm an old fart with a wrench that's been around a long time.
08-03-2021, 10:31 AM
#43
Member
Points
Damn bro, we are old! I know points, and carburetors too! Both are now antiquated, like me! Comes in real handy at car shows when the "wallet builders" can't get their hotrod going. I'm a freaking genius at the Woodward Dream Cruise! Always come home grubby...