Engine/Transmission (1994 - 1998) Engine "over ran" on top end...

[Ben Rumson]

Near the top of a 6% grade hill I noticed a small blazer up the road in front of us suddenly blow a head gasket or something. Smoke was pouring out from under the chasis. I thumped on the throttle to catch up to him and motion him over (so as not to keep driving it and kill his engine).



We went from 65 mph to about 95 mph in a few seconds... but then suddenly my rps reved up and it felt like I had no power to the wheels - the engine just flattened out/reved. I let off the throttle, slowed down, and everything ran fine again. I did not think to look at the guages when this happened - my mind was stuck in a "What the H&#@ is happening mode. After I slowed down a little, I got back on the throttle again and I checked Boost, and Temps - all were good and appeared to be functioning normally and still are.



Please read my signature. Note: I have not upgraded to the heavier 90# springs.



Did I "float"/"over run" the valves (too weak of exhaust and intake springs and the valves began to "float" and not shut properly due the the bigger HP)???



My guess is that this is what was happening... but I've never had it happen.



Any suggestions/confirmations?



Thanks

- Ben

 

[T. Baker]

Could your torque converter have slipped?

 

[Lightman]

Were you running lock up in O/D if so it sounds like your trans droped out of O/D back to 3rd at 95 that would feel like you went into nutral

 

[SlyBones]

Just out of curiosity have you had the PCM upgraded to the latest TSB anytime in the recent past? -- Not implying that you should, just asking if you did, thats all.

 

[Ben Rumson]

No I was not running in OD Lock-up. ... from the feel of it at the time I guess it could have been the the OD dropping out and shifiting back into 3rd - good observation, thanks. It felt like the truck was in Neutral.



Sly - No I haven't had the PCM upgraded. Which TSB are you refering to. I wasn't aware of the upgrade... hummm.



I have 5k miles on this new transmission. Is this something I should call Bill K. about - internal adjustment, TC problem, etc. ?



Thanks

 

[Joe G.]

Ben,



Do you have a DTT smartbox or tc saver? If you do, it will unlock your TCC at high boost and WOT to protect it.

 

[Ben Rumson]

Originally posted by Joe G.

Ben,



Do you have a DTT smartbox or tc saver? ...

Not yet. But from what I'm learning about all of this, sounds like I need to get one. I'm sure I was 36+ Boost and I was WOT at the time running uphill.



Would it be safe to say that there was too much poop for the TC so it slipped? and therefore rather than use a lock-up switch in these types of circumstances, I would want to use a lock-out switch?

 

[Joe G.]

I use a three position lock switch: normal let the computer do it, force lock if hydraulic conditions are right, and force unlock.



The ground wire to the switch is routed thru a door "courtesy" switch mounted on the floor near my left foot so I can easily drop the force lock if I need to. For example in the case of a WOT pass pulling my travel trailer.



From reading your signature I'm thinking that you have enuff power to rip a TCC to pieces. That 91% TC will transfer the power ok. The engine is naturally turning faster and making more noise in that case.

 

[JGK]

Ben,



If you did/do manage to "float" the valves, the result would not be an over-revving of the engine, it would be due to over-revving. When it happens you would notice a sudden drop in power because the valves would not be closing fast enough to cause (complete) combustion, and whatever combustion was taking place would be leaking past the valves.



Worst case, though I'm not sure what it would sound like, the valves would crash into the piston crowns. Now we're talking broken or bent valve stems and damaged pistons.



Sounds ugly. Don't do it.



-Jay

 

[Ben Rumson]

Thanks JKG. Knowing what would have happened if they had floated helps me visualize better what really happened - and didn't happen for that matter. From what you describe, I don't think they floated. I wasn't over reving when it happened. Even with the 3k spring kit, the most I've ever hit is 3200 rpm (my #4 plate out and the stock plate is in at the moment).



Joe, I have a lockup switch now. I did this by splicing into the (#57) wire and when I flip the switch it grounds through the switch to the chasis causing lockup.



How do I make another switch the prevents lockup?? What's the principle or idea involved. (I'm not terribly bright in the electrical department) - but I did fix my Cargo Light! I'd like to know how to make an Unlock switch. Please help.



Thanks !

- Ben

 

[Joe G.]

Ben,



You need a single pole double throw switch with center off.



Cut the #57 wire. Attach the part that goes to the trans to the center terminal of the switch. The other part that goes to the computer goes to one of the outside terminals. The gound goes to the other outside terminal. If the switch is so that the trans wire is connected to the wire from the computer it works normally with computer control. If the switch is flipped the other way it will force lockup if the hydraulic conditions are right. If the switch is in the middle the trans solenoid will not work so the TCC cannot lock (forced unlock). I mounted my switch so that down is normal and up is forced lock.



BTW: If you are looked for a place to put switches the stock cup spiller is taking up good space. I have Geno's Garagage Cup Smoothy and replaced the cup spiller with a switch panel.

 

[amsoilman]

Here is a picture of my TCC switch mounted on the steering colum, just under the wheel. 3-position switch. Center position, the TCC will never lock, FWD position locks the TCC and keeps it laocked. Back position allows TCC to function as designed.

 

[Ben Rumson]

Thanks

Thanks to all.



Wayne Owens, Thanks for the pic - great location for a switch (and no dashboard removal). I'll look to do the same. Also, Thanks again for the air tank you helped me with earlier this summer. My breaks have only flattened out a few times since installing the extra vacuum tank and it was always in reverse under considerable use. It's working great. Thanks.

 

[Ben Rumson]

Update

I got around to calling Bill K. about this and it turns out that the problem was an adjustment of the transmission throttle cable... I had about 3/4 inch of play on the linkage at the trans when at WOT - and there should only have been about 1/8 inch play.



I adjusted the length to 1/8" and my midnight run over the mountain with trailer in tow went excellent.



The "play" was OK when the truck had much less HP, but with my enhancements, I haven't been using as much of the pedal and thus the linkage needed to be tweaked to bring the pressure up sooner to match what the engine was doing.



Thanks again for all your help.



I'm still going to hook up a lock-out switch... . something to do - yeah!

 

[Dennis Garrett]

Here is another photo of the "Center off" Switch, on my truck.

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