Possible trans problem

[Jim Roberts]

Please Help
I was reading a thread that was about the shifting issues in the trans and maybe some pertains to my issues. I have a 1998 3500 express van w/ 5.7 ltr motor. I have ~ 250K miles on the van. Trans was factory replaced at 90k miles, I replaced the motor 15 months ago that had 110k miles on it with a new Injector spyder. Everything ran great until about 3 months ago. I was having low to no power problems. Of course the check engine light was on and the readings were about the throttle positioning switch (replaced), EGR valve issues (EGR replaced) replaced the distributor, Map air sensor and map air unit replaced, Timimg chain and gears, catalytic converters and muffler replaced. Most of what we did made little to no help. As I drove the van, from a dead start, I almost could not move as I had no power. I would pump the accelerator peddle and I was getting a back fire in the plenum and all of a sudden the van would surge forward and run OK and then loose power. Kinda surged when I let off of the peddle too. For a while the van did OK then after reaching running temperature it would go back to the no power mode. THe best and biggest change that helped was dumping a can of BG injector cleaner into the tank along with a can of Sea Foam and a bottle of Lucas injector cleaner all together with a full tank of gas. I followed up with a bottle of Lucas injector cleaner and 1/2 bottle of Marvel Mystery Oil on the next fill up. The next treatment I did was to dump a whole quart of trans fluid on to a 1/2 tank of gas. This actually helped more than anything that we had done and the van started running OK but still not great. I did 4 more treatments of the Lucas and 1/2 quart of Marvel Mystery Oil on a full tank of gas. The van was working good but not great but I had power and no back firing. A few weeks ago all of a sudden the idiot lights went off and the van just went into a mode that was like it ran when the van was new. Everything was working just fine and had all of the power that I needed even pulling heavy trailers. The van ran great for about 2 weeks. Now I am having issues where the accellerator feels like someone cut the accelerator cable and I have no acceleration at all. I floor the peddle and pump the peddle and will get a great surge of power that last maybe 3 to 5 seconds then back to no power and no accelerator. My spedometer is reading 100+ mph at about 30 mph. My check engine lite is on again and on and off my anti lock light comes on. When my trans shifts in this condition, i go from a start in 1st and then the trans shifts into 3rd or higher soon and I am struggling to get up to speed. Today I tried shifting down to Drive and that seemed to make a little bit of increase in speed until I need to shift back to OD. Some one mentioned that speed sensor may be bad. I am tired of changing everything on the van, with others suggestions, and want to find the issue. Is the speed sensor connected to the computer to tell it when to shift and what gear to be in? The problems are intermittent. I had a few great weeks earlier but things work good (not great ) for a while then go to bad. I have been having these problems for the past couple of months.
Does anyone have any ideas?

[Blue Bowtie]

Welcome aboard!

By your description, there may be multiple problems, and among those electrical problems. The transmission is shifted by the PCM based upon inputs from the TPS, engine RPM, gear selector switch on the trans, vehicle speed sensor, manifold pressure, transmission temperature, and various other inputs. These all rely upon electrical connections. The speed indication, service warning lamp, ABS, and other indicators would seem to verify that.

It is probably best to scan the PCM for error codes and active data to help determine where the problems are occurring. This will require a bi-directional scanner and a list of error codes and their diagnostic charts. I've encountered this type of problem and have found poor connections, fuse panels with corrosion, damaged wire harnesses, and other issues contributing to the loss if inputs to the PCM. Changing parts at this point could be a complete waste of time and expense.

[Jim Roberts]

Thanks

What I did today was to disconnect my speed sensor from the transmition. What a world of difference. I have plenty of power. SHifting takes longer to shift or I have to be a a faster speed for the trans to shift but it does shift fine. I can shift the trans quicker by letting off of the accelerator and the trans shifts to the next gear just fine. I bought a speed sensor today and have not installed it yet. Oh also I now do not have a speedometer but that is OK too. I still have the check engine and anti lock idiot lights on. In talking to someone today and they suggested, and I was curious too, that with the speedometer pegging over 100+ mph the computer is shutting the engine/trans down to a limp mode until the speedometer reads some reasonable speed (not the speed that I am driving) and that is why I am getting no acceleration when the speedometer reads over 100+ mph. This has all gone away with the disconnection of the speed sensor. I will install the sensor and report back. Thanks for you reply. I will also check the other suggestions that you posted too to let you know what I discover.

[Blue Bowtie]

If the VSS signal is faulty, that will affect the transmission shift points, the speedometer (of course), and the ABS since the EBCM receives the rear wheel speed info from the VSS.

None of that affects the stumble/hesitation problem you described, but a good VSS signal may clear up some of the problems. Make sure the problem is in fact the sensor and not the plastic gear or the electrical connector.

[Jim Roberts]

I replaced the VSS and all is working now. No check engine light or Anti Lock light are no any more. My spedometer is reading correctly, Trans is shifting OK.

Thanks to all and a Merry Christmas to all
Happy Motoring !!!