Engine/Transmission (1994 - 1998) can 300 hp injectors be causing my transmission shudder?

[ddechris]

Now the obvious is that yes, more power is too much for the stock converter. But, I upgraded with a TCC and VB from BD. The slippage went away with the upgrades, but there is still a shudder or chatter when the torque converter lock-ups on a slight grade OR when the engine lugs down without unlocking the converter. This is very irritating since most of the local roads around here are 45 mph ... . right at lock-up. I'm toying with turning up the line pressure, replacing the TPS with a pot to move the shift points or other work arounds. BTW, my transmission shifts into OD at 30 mph unloaded, is that normal?



But what I am curious about is if the 300 injectors just don't burn right at low engine speeds. If I'm pulling a load or just step into it more, the shudder goes away. But, it is most noticable when I'm poking around trying to keep the economy up. The TCC will unock/lock in the 1200-1300 rpm range and I can feel the shudder up to around 1500 rpm. Another clue is my poor mileage for this poky kind of driving. Most of the winter I was getting 15. 5 mpg. Since spring, that's gone up to 17 mpg. I did get 20+ on a couple tanks on an all highway run from PA to Miss.



Has anyone with 300 injectors and an auto experienced this?

Anyone have some left over 180 or 215 injectors. I want to swap out the 300's and narrow down the root cause before looking an any more upgrades.



Thanks for any help, Dave.

 

[vssman]

I'm no transmission expert but I believe light pedal pressure gives you low line pressure and may be causing the shudder. Someone else with more experience needs to chime in with potential fixes...

 

[Vaughn MacKenzie]

It may be hard to tell if the shudder is coming from the transmission or engine. The engine on my '98 shudders between 12-1400 RPM, caused by the injectors not the transmission. The 300s are known to cause this and I'm guessing that's what your problem is. Does the shudder seem to be at the same frequency as a slight misfire on one cylinder, or a more rapid vibration accompanied by a slight RPM increase like a slipping transmission? The 300s aren't that great of injector and I'm planning to dump mine soon.

 

[raychem]

The 47's also have a weak od section, it is a classic case of the next weakest link and is why 47 are more sensative to power increases over the 48. You may have to go over the internals since the tc and vb will expose the other problem areas in the trans. Vaughn also has a good point about the shudder which normally causes a slight engine inbalance between 1100-1300 rpm as a general rule. I don't know where your located since it is not filled out but call me @ 786-543-9176 and I will help you out where I can.





Richard

 

[ddechris]

The more I've been reading here, the more I've been suspecting the 300's, but it's nice to know that someone else has the same combination and sees the same problem as a sanity check. Yes, it seems more like a cylinder miss. I've been debating having my wife count the shake of the 4wd shifter so I can figure out the frequency.



Over the weekend, I patched in a TC Clutch override switch (I opened the ground circuit from the transmission to the controller) so I could drive in OD without the shudder since the local speeds keep me in that range (45 mph). It was a lot smoother ride this morning, but I thought I still noticed some of the shudder at 40 mph which is still down in that 1200-1400 rpm range. With the fluid coupling, its not as harsh and harder to notice.



BTW, if you put a similar switch in, the circuit needs to be closed when you start the truck or the transmission goes into limp mode and the only way out is to re-start. Once running, you can use the circuit either way.



So, if I ditch the 300's, what would be a good injector to go to? I already have the plate for a little extra power, so I might be happy with stock. But, if there is a higher performance injector that can improve my efficiency, I could justify the upgrade.



- Dave

 

[Vaughn MacKenzie]

I would consider Dynomite Diesel injectors, as far as I know they're the best pick for a 12v especially if you're not looking for a big fueler. Their stage IIs are advertised at 70hp if I recall and list at $499.

One thing I always do is leave OD off when driving around town, I don't turn it on unless I'm going to be traveling at least 50. That will help the low-RPM engagement issue.

Another thing to note, 12-valves do have a history of having a slight miss at low RPM and throttle. Both of my trucks have been affected by this and it's a fairly common problem. My theory is the mechanical lift pump might have something to do with it since it pulsates the fuel so much that's being delivered to the injection pump.

Vaughn

 

[ddechris]

Vaughn,

What timing are you running? I sent an email to one of the TST tech guys and he recommended changing the timing from 14 to 15. 5 to "better match the injector. " I might try this first before swapping the injectors.



- Dave