Transmission Nightmare 4L80E

[scooter]

I'm having a bad month...first some background:
1996 Chevy K2500 Suburban, 6.5L TD, 4x4, 4L80E
- FSD Cooler with about 2 years on new FSD
- Plastic 6.5L TD Cover off
- replaced wastegate solenoid 2 years ago
- replace injectors (all 8) 2 years ago

Decided to change tranny oil about a month ago. Shortly after (about 400 miles), it started shifting very strangely. First symptom was at over 50 mph, it didn't want to go to overdrive---just kept on revving up to 3000+ RPM, let of on petal, and it goes down to idle, put petal on---back up to 3000+.

Took it in to a tranny shop. They couldn't find anything with the outside checks, so said they needed to take the tranny off to check the internals. Found a boatload of problems, including the 3-4 clutch and clutchplate completely worn. By the time they listed all the parts that needed to be replaced, it was up to just about the cost of a new rebuilt swap.

I decided to go ahead and have them swap in a new rebuilt from Chevy. Problem is, they continued to have shifting problems with the new tranny. They took it to a chevy dealer to find out if it was a tranny problem or other. The chevy dealer determined it was an engine performance problem, possibly fuel delivery. Basically, the engine is sending bad info to the computer, which then sends bad info to the tranny, causing bad shifts.

Symptoms: Once warm, hard banging shifts from 1-2 and 3-4. Sometimes goes to neutral state from 3-4. I noticed that a huge amount of smoke blows when I try to accelerate at about 35 mph sometimes. It also died at 50 mph on my wife yesterday as she was driving down the road. She was able to restart in neutral....

The Tranny shop actually spent a lot of time trying to diagnose this, and they think its the computer causing the problem. He actually went through each input to the computer and measured as normal signals from all the sensors. The output is just bad going to the tranny. He also measured all the grounds and they were all .1 V or less....

What else can I do to narrow this down and make sure it is the computer or maybe something else? My friend suggested changing the battery cables..

Sorry for the long post, and thanks in advance for any help.

Cheers,
Scooter

[JohnC]

Diagnostic codes?

[scooter]

Yes...the tranny shop reported a Code P1216 - Fuel Solenoid Response time too short.

I just talked to him...he measured the fuel inputs to the computer as being withing range, but this was during idle with a multi-meter....it is possible the this code is being thrown under driving conditions? Does this point to the FSD? Should I try connecting to the old FSD that is still on the pump to see if I get different results? It never went bad, I just installed the FSD cooler with a new one as a preventative measure.

Thanks,
Scott

[scooter]

Oh yeah...I forgot to mention. They also discovered that the petal sensor was bad, and replaced it (at the tune of $365 + labor ($90))...apparently, it was not sending the right voltage to the computer for the softer petal positions, only correct for the "stomp it into the floor" position...

[Tough Guy]

Pull the wires off the batteries and reinstall, then take it for a spin. If the system isn't rebooted after a repair it will sometimes not work after the repairs.

Cheers

[scooter]

Tough Guy: Will try it over the long weekend. I did this after the initial tranny oil change and it didn't help since the clutch & plate were worn out. I'll try it again now that everything is replaced....

Does anyone know if you get all new speed sensors and the like with a rebuilt tranny, or should I be checking some of these puppies out?

Thanks,
Scott

[Uncle Wally]

Scooter,

I would expect a new speed sensor with a new trans, but I would check to make sure. You didn't mention if this was a 4x4 or not. If it is, check the speed sensor in the t-case. Pull it out to see if there is metal fillings or debris buildup on the magnet. That can throw a few wierd codes.

Keep us posted,
Waldo

[Dimsdale]

I had a similar problem that was extremely difficult to diagnose: limp mode, no TCC lockup, some code in the computer I can't recall (1860?). Tended to act up more in wet weather and the morning, but eventually became constant.

Turned out to be a "crushed wiring harness" around the area where the bellhousing and the firewall are in close proximity. No idea how that happened. Probably some assembly issue. A splice job fixed it.

Might be worth a look.

[scooter]

I tried a couple of things yesterday:
- Disconnected batteries for 10 minutes to reset the computer : No change -- still shifting badly
- Took out fuses, cleaned them with sandpaper, sprayed them with WD-40 : No change

I started to try to take the speed sensor out of the Transfer Case, but then I realized two things:
1) I don't really know where the speed sensor is.
2) I didn't have a long enough torx screwdriver to remove what I thought was the speed sensor...

Question: Is the speed sensor on the lower part of the transfer case, attached with 4 torx (Star) screws? It's about 6 inches long and about 3 inches in diameter. Or it it one of the sensors on top of the TC? What color are the wires?

I looked to try to find a squashed wiring harness, but it was getting dark, so I'll have to check this again later...

Thanks for all the suggestions. Any input on the Code P1216?

[Uncle Wally]

Scooter,

The speed sensor has a 2 or 3 wire connector going to it. It is on the top side of the transfer case above the yoke for the rear driveshaft. It is held in place by one 13mm bolt.

At least it is for my truck, which is a 94 1 ton with a Borg Warner 4401. There could be some differences with other models of transfer cases. If you knew the model of t-case, I could tell you where the sensor is at by looking at my factory manuals.

I think that it's a safe bet to say that whatever you where thinking about removing is just part of the case and if it's the same as mine, it only holds the sensor and the seal for the driveshaft yoke.

When you do get it out, I would check to see if it looks like there are a lot of metal filings or other material built up on it. I'm not sure how you would test it without an oscilloscope and a reluctor ring to trigger it. Maybe someone else has a means to do that.

Waldo

[scooter]

Thanks Uncle Wally, I think I know exactly the one you are talking about from looking at it last night....or maybe not...it seemed more like a 17 or 19 mm bolt....I'll have to look again. It's at home, I'm at work...maybe I'll run home for lunch and take a quick peak. :eek:

Just have to make sure not to ruin these jeans with grease like I did yesterday with my nice jeans :mad:

Thanks...

[mklein]

The 1216 wouldn't have any effect (affect?) on the transmission shifting. Hell, the PCM won't even throw the lamp on for it. Can you get ahold of a good diagnostic tool? It would really help to see the trans info while you are operating the truck.

[scooter]

I stuck my head under the Transfer Case at lunch time...actually a good time to do it with lots of sunlight! I think I saw the right sensor now...it's at the very top of the Transfercase, pretty much in the middle, facing back to the rear end. I was able to get a 13mm wrench on it, so I assume that's the one. It was hard to see the wires from my angle, but when I get some grubbies on, I'll take a closer look.

I don't have a diagnostic tool....how much are these gadgets? Is it something I'll swear I could never live without once I invest in one? Any recommendations on what kind and where to get one? Can you rent them?

Thanks....Scooter

[LanduytG]

Its sound like mine. Cleaned all the connections and it helped. But after I took off the anti lock brake speed sensors and cleaned them up the problem went away. Someone about a year or so ago had the same problem and the wheel sensors took care of it a well.

Greg

[scooter]

By the way, I have 170,000 miles on the OD, and I picked this Suburban up from Ohio, so yes, it has rust all over underneath. Maybe one of these sensors has corroded connections....I assume the ABS sensors are somewhere on the brakes? Do I need to pull of the wheels to get to them, or can I find them on the back side of the wheel assembly? (I know, I know....lazy boy...)

[Tough Guy]

Keep us posted as to what you find...

Cheers

[LanduytG]

You will need to pull the wheels. Mine now has 174K and it first started to act up at about 157K.

Greg

[CareyWeber]

Originally posted by LanduytG:
Its sound like mine. Cleaned all the connections and it helped. But after I took off the anti lock brake speed sensors and cleaned them up the problem went away. Someone about a year or so ago had the same problem and the wheel sensors took care of it a well.

Greg Greg,

Once you get the wheels pulled how do you get the wheel speed sensor out to clean it? :confused:

I looked at it when I had the wheels off Sunday, but it looked like the rotor would have to come off too (My truck K3500 SRW).

Carey

[Dihrdbowti]

Scooter the code P1216 shows as Fuel Solenoid Response Time Too Short.

[Bill Voitel]

P-1870 is a trans slip code if no slip code keep looking to electrical problem. I have heard the guys in our shops bi**hing about the connectors on the 4L80E corrosion & stuff

Bill ;)