Transmission Destroyed By Python 871xp

Sorry, KP, bad writing form on my part. That’s the problem with “it” – to what does “it” refer? AAMCO did fix the transmission, no problemo; that’s what they do best. They are now a full service auto repair facility. When I first arrived, most likely in a somewhat agitated state after being left standing in the parking lot at Circuit City with the installation supervisor and installer refusing to look at their work, I understood the AAMCO manager to say that they would be able to reinstall the alarm system correctly. I think their electrical specialist must have taken a look at it and said, “no way!” So, the transmission is repaired but the alarm remains as it was when I arrived at AAMCO.

Now the update: I started the van ready to take it for a test drive and noticed that the engine is running unusually fast. I depressed the accelerator and the engine seems to die for a couple of seconds and then resume running. I let it warm-up for a minute or two and noticed that there is now a pronounced hesitation lasting a few second when I first depress the accelerator pedal (e.g., as when pulling away from a stoplight). I also noticed that the shock sensor LED illuminates periodically (The shock sensor was reattached just below the dash by its single strand of electrical tape and is clearly visible.). The LED may be responding to the increased RPM when the accelerator pedal is depressed (remember boys and girls, the ground is disconnected; I was right when I asked the turkey to remove the +12 VDC inputs and not just the ground as were some of you). I turned the van off and returned to the shop and told the manager about the new problem (new since Circuit City worked on my vehicle, but the engine problem was present when I drove to AAMCO).

He offered to have the van towed to a local Ford dealer. I asked if he could have his technician remove the two 30A fuses to the alarm control module. The electrical specialist had already left for the day (I really think this guy doesn’t want to touch this mess; I had asked earlier that the +12 VDC be removed but I may not have been clear that this could be accomplished by pulling the two 30A fuses [I’ll have to check the installation manual tomorrow, it’s at AAMCO, and make sure that there aren’t other +12 VDC inputs to the module].)

He then drove the van from his parking lot back into the garage for overnight storage. (Oops, he hit his garage door which was partially lowered with my conversion top; no, I didn’t’ ask him who his insurance company is so that I could file a claim; if it didn’t crack the fiberglass, I’ll fix it myself with a little touch-up paint.) He commented that the van ran better after the initial hesitation; I replied, ok, but that’s not how it ran before Circuit City got their claws on it (Am I showing a little anger yet?), and I didn’t want to risk engine damage too. He then said he discovered that the alarm system was working and demonstrated the armed and disarmed functions (the vehicle was stationary, i.e., no transmission gear motion). I stopped him from trying other alarm functions and quickly made sure that the remote-start safety switch was off.

I mentioned early in my posts that I know relatively little about electronics and that’s true from my perspective. Actually, I have worked with electronic circuits in my research for over 30 years. For example, I design and construct computer-controlled circuits for producing small, well-controlled electrical pulses for stimulating brain tissue (one of the experimental techniques that I’ve used for my work; if you’re really curious and bored on a Friday night, you can see a few photographs of one of the labs I built here: www.wings.buffalo.edu/aru/BSRfacilities.htm). And of course I had my graduate students assembling the computers used in this research one IC at a time before the prices dropped so much that it was much cheaper to modify completed computer systems than it was to construct them from components. OK, now you have some background. I still don’t think that I know very much about electronics, but some people might think otherwise.

Now back to removing the ground wire as a method of ‘unpowering’ a circuit board. That’s almost as stupid as not using the tilt switch for the alarm safety. The alarm control module has other negative (aka ground) inputs. (Thanks to the posters who reassured me when I only timidly suggested this was a potential problem.) This can provide a current sink, thus powering-up the device as evidenced by the fact the alarm control module is working with the ground wire totally detached! Now there’s one other point. The negative going inputs can complete the circuit for the module’s power supply, but this isn’t the way the circuit was meant to operate. This could make the alarm control module very erratic and create even more problems (e.g., defeat current- and voltage-limiting circuits). OK, see why I wanted the +12 VDC inputs disconnected from the alarm control module by the Circuit City people, and see how off the wall they were when they only disconnected the ground instead?

Sorry, I didn’t mean to sucker punch anyone here. I do feel that I have just a basic understanding of these things but that hasn’t stopped me from designing and building some pretty sophisticated circuits for use in my research. (I’m the old-fashioned type of professor/scientist who learns the skills needed to accomplish the task at hand and doesn’t let the limitations of his skills determine the task.) And I suppose I do have kind of a home here on the12volt.com, even though I’ve little experience in automotive electrical work – 12 VDC was my favorite power and control levels for the CMOS circuits that I used extensively in my research (I avoided TTL whenever I could use CMOS.).

The point behind the 'electronics shouldn't destroy the tranny' comments are the fact that the only electronic parts of the tranny are solenoids.  A 'typical' tranny has two shift solenoids.  With no solenoids energized (ie safe mode, limp mode, etc) the tranny is in 2nd gear.  When sol. A is energized and B. isn't you would have 1st gear.  A off and B on would give you 3rd, and both on would be 4th (and so on for how many gears you have).

All the 'electronics' are doing are allowing tranny fluid to flow, to allow the tranny to operate.  You can pop those solenoids in any way you want and all that will happen is that you will end up in the wrong gear (which, as we already discussed, would cause engine damage before tranny damage).  The clutch of the AT works off of they hydralic side of the tranny.  I hope this explanation makes sense to you.  Of course, as we all know, we haven't seen the schematic of this tranny and it may be different.

I would completely unplug the harness from the brain, if the brain is accessible.  The tach wire is the only wire that could possible cause any issues.  I've hooked low current transistor based input circuits to car circuits that could pull the signal down far enough for the circuit to be unreadable.  This was with custom built experamental stuff, but it still happened!

Hopefully you'll have it back in your possession, running great, in a short time.

If you run across those references again, “Installer_mss,” I’d appreciate the links. The only failures that I’ve seen after a few hours of online research at the forums, performance shops, and the posted TSBs is not shifting into some gears and, of course, the usual slipping. Both of these problems are most often progressive and appear much more frequently on models before 1998(?). And the ATF usually is not nearly as clean as that removed from my transmission. Also, I’ve found nothing on the PCM being fried at the same time mechanical damage occurs.

I’ve only been reading about Ford transmissions for a short time now, and the 4R70W just the past day or two. So obviously I don’t have the experience that many of you have reported. I appreciate your comments and would like to review any technical reports on failure rates that you find.

Thanks for the lesson, Kevin. As I stated before, I didn’t even know that automatic transmissions were now electronic. The last automatic transmission that I looked very closely at was a 1962 Chevy Powerglide. My Jeep Wrangler has a 5-speed and I try not to get too close to the power train in my 1988 Ford chassis MoHo. (But now I may crawl underneath it; my curiosity is aroused.)

The 4R70W must have only 4 speeds. The way it smoothly and decisively shifted among them during my 2,300-mile trip home, I would have thought it had more. I understand the logic states dictated by the two solenoids and the ensuing 4 gear ratios – you provided a very good, simple (at my level) explanation. And I figured that there must be what I would call a “safe mode” for when the electronics fail; that appears to be 2nd gear (and I see that you use that term too, so I’ll assume that this is the correct term). 

I conclude from this that the transmission would not ‘get lost’ between gears because of a solenoid-related problem. So I’m back to my initial subjective impression, the transmission may have been shifting radically from 3rd to 1st to 4th or to whatever gear regardless of the engine RPM and power train requirements. Remember, I thought I had a kill circuit that was grounding the engine, so being rather stupid I depressed the accelerator more when it began to stall. And as I mentioned before, the 5.4 liter V8 scoots this full-sized van down the road real well. I generally drove slowly on my trip from Phoenix (often under the speed limit when the road was very bumpy), but I did have to accelerate quickly a number of times when entering the expressway from the entrance ramp, and this dude rolls! Now you have me even more worried and thinking I will have to take this to regular civil court and not to small claims court. What if the engine is damaged too? Should I be going for a full power train replacement? The lawsuit may be escalating..

The PCM is fired (not literally, but operationally). I don’t know if it could oscillate on its own, but understanding a bit more about how the transmission works only makes me more certain that the alarm system must have interfered with the PCM’s operation. The stalling-like signs that I interpreted within the erroneous context of an ignition kill circuit would be very much like what I would expect with the engine racing at higher than normal RPM in 1st gear and slamming into 4th and slowing down very abruptly. And then perhaps moving to a much higher RPM in 2nd gear or even back down to 1st gear. (Man, "Ford trucks are tough!") The symptoms are quite clear now, but the exact cause other than PCM malfunction shortly after the alarm/remote-start installation at Circuit City remains unclear. (Recall that I heard a very loud power train thump and bump immediately after deactivating the anti-carjacking feature.) Perhaps the people at Ford engineering can help.

That's very interesting -- with no solenoids energized, the gear would be 2nd; with both solenoids energized, the gear would be 4th. I'm guessing by my good gas mileage at 70 to 75 mph that 4th gear must be pretty high, and the quick acceleration suggests that 2nd gear must be pretty low. I'll have to check the gear ratios in the Ford literature, but abruptly shifting from 2nd to 4th and from 4th to 2nd might have caused the mechanical damage. Very interesting and coincidentally a state shift from all OFF to all ON. You may have put me onto something . . . thanks again, Kevin.

Solenoid failure should have locked into a single gear, not caused it to shift radically between gears. (Locking OUT of a gear is a way these transmission have had problems. This IS NOT what happened.) All of the information that I've found is that this is a great transmission . . . do you have any data? The post-1998 manufacture seems to have a particularly good track record. I'm still waiting for the links showing problems? Finally, did you miss the part where the PCM was fired?

That's very helpful, Richard, you've certainly nailed the symptoms. Now I'll have to see if I can find a qualified installer locally not in bed with the boys at Circuit City. I was stupid, I thought the ignition was cutting out because of my mistaken belief there was an ignition kill relay. I depressed the accelerator more to try to keep the engine running (actually, it worked but probably exacerbated the damage). I drove back to Circuit City (2.4 miles) not realizing that the transmission was probably being destroyed enroute. When the Circuit City people refused to look at the problem, I then drove further to the AAMCO shop not thinking it was really a transmission problem but not knowing where else to go for help. With hindsite I may have minimized the damage knowing about this possible problem, but I didn't even know that the automatic transmission was electronically controlled (apparently some ASE mechanics don't know this yet). In the 5 1/2 days this discussion has been running, you're the first person to report a similar experience. This was the primary reason for initiating this thread -- anybody ever have a similar problem? Instead, I think I put a lot of installers on the defensive (with some notable exceptions). And at least one has been feeding the installation manager at the Amherst, NY Circuit City where this incident occured. (And he may have recruited a few of his buddies to try to throw a few red herrings on this thread.) Thanks a lot for reporting your experience!!!