Four years ago I purchased a 1939 Dodge pickup model TC.
The seller started the project and never finished it.
I was told it was 80% done. What I wasn't told it had 80% left to go.

Here is the deal. The truck has a 5.2 Magnum engine (completely stock) from a 1994 Dakota. It has a 1983 727 Torqueflite transmission.

For obvious reasons, this is a total mismatch. The 5.2 is computer controlled, and the transmission is hydraulic. I was assuming based on the 1994 model year engine that this is an OBD-1 system that only controlled the engine diagnostics, and not the transmission.

Well guess what? I have two codes showing on an OBD-1 scanner.
The codes are open, or short, in the overdrive solenoid relay, and open or short in the torque converter lockup relay. Apparently the computer is trying to analyze systems that do not exist on the 727.

Having said all of the above, here is my only real issue. I can run the truck up to 60 mph and it will run all day long real well. However when coasting down through the 45 mph range, the engine shuts down. Not every once in a while, but every single time.

Now, I can go to neutral and restart the engine, and as long as I stay under 45 mph, the truck runs good. But when you take it back up to 60 mph and then coast down to the 45 mph range, it shuts the engine off.

I am at a loss to even try to figure this problem out.(other than change the transmission and get one from a 1994 Dakota and get it wired into the computer).

BTW..The 727 transmission does a speed sensor solely for the VDO electronic speedometer. There is no other electrical wiring on this transmission. The speed sensor, which came with the speedometer is wired to the speedometer, and nothing else.

Does anyone have any ideas to overcome this mismatch to where the truck will coast down past the 45 mph range without shutting the engine off?

Thanks

One of two things can do.One = locate a computer from a 5-speed truck. Two = go to the junk yard and get trany harness for that year of truck. Also you call HotwireAuto.com at 1-479-243-9115 and they can give you more info or reprogram your computer to work with that combo.

Some fuel injected engines will turn off the fuel on a long coast. It sounds like this is happening to you. They probably keep the torque converter clutch engaged to keep the engine turning. Then when you get back on the throttle fuel starts again and you keep on going.
Sounds like you could use a matching overdrive transmission which would fit in your pickup no problem and make cruising easier!

R.

Hmmm.... if you can scan for fault codes, can you use your scan tool to see what the computer thinks the vehicle speed is? Since your issue is speed-related, me thinks you need to program the computer to compensate for the tires you have on the truck

Besides your transmission-related computer outputs you noted, there are INPUTS to the computer from the transmission that the 727 can't generate, namely - output shaft speed (driveshaft speed) which the PCM uses as an indicator of how fast the car is going. If the computer thinks the truck is going "too fast" (based on speed rating of stock tires), it will shut off fuel.

intresting topic

I'm thinking you need a vehicle speed sensor of some sort...that and getting the computer reflashed to a manual tranny, or adding into the harness some dummy loads (resistors) for the missing sensors...

I have a manual tranny computer for sale, but it's for a '96 ram 1500, so it's the OBD2-jtec controller. dunno if it'll plug into the older harness.

Thank you all for your replies and assistance. They all seem very logical to me. I did not include this thought in my original post because it was getting rather long. I have given consideration to converting the 5.2 Magnum engine over to carbureted and just doing away with the computer. I am sure this would open a whole new can of worms.

For one thing, we are running an electric fuel pump which is delivering a confirmed 50 psi. That is way to much pressure for a carb, right? I haven't checked on a fuel pressure regulator yet, but surely one is available.

To use a mechanical fuel pump, which this engine wasn't designed for, requires an older LA 318 timing cover, longer cam shaft to run the pump,etc. and I just don't care to get that involved. My skills are somewhat limited. However, I will through this thought out there for your opinions and see what you all think. I am not really looking for a cheap fix for my issues, just the easiest one. Thanks again for your replies.

Resistors won't work to fool the computer. You need a relay. When relays de-energize the collapsing magnetic field creates a voltage kickback, this kickback is what the computer is looking for. Resistors will not do this. You might be able to just hook some relays to the wiring that control nothing so mimic the kickback. But I am not sure it would fix the engine shut off issue. I think it would be wise to consider swapping in the trans the computer is looking for, OD will help mileage.

I really do agree that a tranny swap would be the easiest way out of this mess. I believe the 94 Dakota's had 46RE transmissions. I would need to insure it would have a wiring harness with it. The challenge then would be to get it wired to the computer. And I do have the entire 94 Dakota wiring diagrams (46 pages worth). Thanks to all for your input, and suggestions.

BTW..There was a suggestion to add an O2 sensor. The truck already has one. However, the truck has true duel exhaust, but it only has one O2 sensor on the right side exhaust pipe, about 8" below where it attaches to the exhaust manifold. There is no sensor on the left side
exhaust. And it has Magnaflow mufflers, and there are no catalytic converters. This all adds up to very little back pressure.

so there is a speed sensor installed and working? the fuel injector cut-off on coast down kicks in when the PCM detects a slowing vehicle speed, higher vacuum signal than idle, and a closed throttle. it stops grounding the injectors as a way to save a small amount of fuel, and yes, the transmission will be in "converter lock-up" at the same time to stop the engine from stalling out completely. the PCM will turn the injectors back on at around 22mph...of course, if you have a non-lock up converter, that's not going to matter.

I think you have 2 options here. either A) get the right trans and wire it in place, giving you OD and torque converter lock-up both of which will help improve mileage, or B) put a carb intake on it.

all you REALLY need to run the engine via carb, is the intake, carb, older electronic distributor with an orange box or MSD type ignition, and a fuel pressure regulator to dial down the pressure at the carb. the magnum/carb intakes are pricy, or you can hit *shudders* ebay, and pick up a generic "dual bolt pattern intake" for about half price. it's a dual bolt pattern (LA/Magnum) copy of the air gap intake. just search for "Magnum/LA intake" it usually pops up

I think some folks have hit on the right points. this response is long but I think it needs to cover all my thoughts.

I also believe the Maggie ECM is cutting fuel during your coastdown. Ford’s EEC-IV did this on the 5.0 in the 80s-90s (other OEMS do it too, but I’m not familiar with them). Parameters required to prevent a stall (and this should be pretty universal) are sufficient vehicle speed, closed throttle, high vacuum, and above 1500 engine RPM (that’s a Ford # there). My 88 Lincoln LSC has a MPG computer and it is really evident when fuel-cut kicks in, to the point that it is advantageous to coast down long highway hills in D instead of OD so as to stay above 1500. The max coasting # I’ve seen is around 150 MPG during a 75mph coast. Anyway…

You have an OBD1 ECM that does not control the trans shifting but it does control the OD and LU, and LU is your main problem. Torque converters are not as effective in back-driving, so when the fueling stops, the engine compression stalls the converter, and the engine stops immediately.

Your 2nd ‘problem’ is that without OD you’re probably above the 1500 during every coastdown. You could wire a switch to the ECM so that OD is always off, and that will solve 1 diagnostic code (but that shouldn’t be causing you any issues anyway). The LU solenoid needs to be solved. I am surprised that the ECU is still doing the fuel-cut when it is not getting vehicle speed info (VSS) and sees a LU solenoid problem. Bad design/response. VSS info is crucial for smoothenss when vehicle speed slows approaching a stop, so sending those wires to teh ECM might be a future issue. Pulses/mile of the VDO sender may/may not be compatible, will make the ECM think you’re going slower/faster than you are and that might lead to buck at slow speeds if the fuel’s cutting off.

Your options:
There is a 727 that has electronic LU but they aren’t real common. I believe they are from the TBI truck/van years of 88-91 (I’ve read about them on here). I think the LU is hydraulically activated but the solenoid releases it (or vise versa) so that may not mesh with the Mag ECU if it is running an on/off solenoid. Although, if the Mag and TBI LU is wired differently, you might be able to use a relay to reverse the logic in between.

Next option is a hydraulically-goverened A500 or A518, of course.

BUT…
But since the ECU is cutting fueling anyway, maybe a hydraulic LU setup would work? I would think an 83 727 would be LU unless it came from a 3500 van or something HD. Torque converters are not as effective in back-driving, so when the fueling stops the engine compression stalls the converter.

Does your current trans have LU? When does it disengage?


And –
If you decide to go carb, be aware some fuel pumps may not like being choked from 50 psi down to 5-7 and it may shorten their life. You might not notice this until you go thru 2-3 pumps and see a pattern, harder to notice if you don’t drive it often.

Please let us know how this goes, I think a few of us are interested in the solution!

I wouldnt opt for a different trans or carb just yet. I helped a friend do a conversion harness for a OBD1 harness into a 68 Fury with a regular 727. He ran a summit speed sensor to the pcm for vehicle speed. He used the auto trans computer for awhile and no issues. He did have this issue previous and the vehicle speed sensor issue fixed it.

I personally think/know the trans codes are not your issue. I believe it is the lack of vehicle speed input to the ECM. I would recommend using this interface http://www.ebay.com/itm/DAKOTA-DIGITAL-U...=item564844430f
to get the desired signal to the ecm from your existing speed sensor.

By the way, you may want to ensure the brake switch is wired to the computer as an input, along with the P/N switch. You want to ensure the engine knows the vehicles is in gear and when you are on/off the brake.

I would also look for a manual trans/mopar performance pcm. It may have alittle bit better driveability to mimic more of how the computer is actually functiong (no trans controls what so ever).

Look in the truck parts forsale section and there was a computer forsale there that may help. I would be happy to help trouble shoot farther if you want to PM me.

The last option is sell it to me

Good luck

NO the "RE trans did not start til OBD ii in 1996; any A500/518 from 89-95 would suit your needs, or in "RH" terms a 42 44 or 46 RH would be perfect the 46" being 727 based the "42 and 44" being 904-based.
the RH" vs RE" only telling whether the governor circuit would be hydraulically or electronically controlled. I see several possible "ways out" in this situation. they did use a 3 speed auto in many full sized vans well into the 90s. so a computer from one might be an idea. most were 3.9powered though IDK if they put a 3 speed behind a V8; but any tranny taht will bolt to a 3.9 will also bolt to a V8. You are NOT stuck looking for specifically a 94 transmission!
the carb conversion isn't hard. I have installed Magnum heads on older LA engines that I have had drilled for the old LA style intake. they do make intakes that allow you to mount a carb to a Magnum that don't require redrilling the heads. the regular elec ignition distributors for any Smallblock will drop right into that engine.

Geez, I didn't intend for this forum to turn into a rocket science discussion. But that is why I turned to this forum because I knew there were Mopar people out there that were much smarter than myself.
As mentioned in my original post, this is a mismatch setup from the get go. Now what I need to do is take all of your suggested opinions and determine which way to go to solve the issue. All I really hope for is to get this truck to run down the highway without the engine dying. If we can accomplish that, I will be extremely happy. I have some friends that will take your info, and we will find a solution. I just don't know how long it will take. Thanks again to all of you for your input. It is appreciated!!! I will keep you posted as to when we have a fix, and what it took to do it.

I stand corrected on the 46RE tranny. After further reading, you are exactly right on the A/500 - 518. I also read that these were redesigned 727's but with a longer tailshaft to accommodate the overdrive. BTW...My current Lokar 727 floor shifter obviously does not have the O.D. position. Lokar doesn't make a shifter for the 500 - 518. This is one bad thing about after market street rod products for Mopar's...Few & far between.

Here is something else I read regarding current carb intake manifolds for Magnum engines. It may not be as simple as just bolting it on and you are done. The intake ports must match the head ports perfectly. If the intake sits to high it will need to be shaved down. If it sits to low there are several different gasket thicknesses which allow you to build it up to get a good match. Has anyone had this issue?

I believe the OD on the 500 and 518 is actuated ONLY electrically, and that there is no detent in the shifter selector.

Haven't heard anybody talk about the intake port issue. I believe the Mag ports are taller/narrower than LA, and LA318 and LA340/360 have different sizes. I've not heard the manufacturers make much mention of port match, although the issue surely exists to some extent.

A recent check of Lokar.com shows that they are now making floor shifters for 518/904/46RE transmissions. That is good news if I opt to change tranny's.

Also, some questions were raised in earlier posts as to whither I have a lockup, or non-lockup torque converter 727.I need to be real honest in saying I do not know. Nor do I know how to identify the difference.

Would the tranny case ID numbers help to identify if is , or not?
I did use the case ID to determine the year of manufacture as 1983
but I don't know what vehicle it would have been used in.
(Car, truck, van)

I found the following info at allpar.com...

"You can identify a lockup 727 transmission because it has about 5/8" of the end of the smaller input shaft machined smooth. If the splines go out to the end of the shaft (except for about a 1/8" bevel), it's a non lock up transmission."

This is great to know but doesn't help me much right now because the 727 is mounted in the truck.

The transmission is not the issue. Making the computer happy is what needs to be done.

Verifying it has a Park Neutral switch input & brake switch input, as well as vehicle speed is what need to be accomplished.


I have ran an auto trans pcm in a manual trans dakota, and no drivability problems. I would verify the other stuff first.

94/95 - the OP was talking about obd 1. mine was the same year.

I have helped with this exact swap, and actually made the harness for the swap. if you really want to keep the efi and the 727, it is very doable.

nothing like hands on experience.

Unfortunately not so. I have two cars done in running (both friends/family). I have advertised for about 6 months, and havent sold one. They are 275 for just the harness. I thought that was very reasonable.

Oh well...

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I just may need one of your harnesses to solve this issue. But it won't be for another couple of months. Working on other projects at present time.

In my original post I mentioned the speed sensor for the VDO speedometer. I also stated there was no other electrical wiring on the 727. That is wrong, I completely overlooked the neutral safety switch which is wired and working properly. My mistake.