New Here. '94 3800. Bucking. Misfires?

[fordro]

I just bought my second Lumina APV today. Got a good deal on it knowing it needed a tune up. This new van starts right up, idles fine, but within 30 seconds, starts to buck and sounds like it wants to die. All you can smell is gas. The van has 214,000 miles on it. Had the engine rebuilt around 140,000. There was a receipt in the glove box for the TPS, Crank, and MAF sensor in September of 2010.

I am going to do the plugs and wires tomorrow and see if this fixes the problem. Are there any other things I NEED to address while I'm under the hood? Would there be any other things associated with these problems I might be overlooking? Any help would be appreciated. Thanks.

[LMP]

..and what if you get in and start driving the car right away? Too much gas? WOuld it burn it if it was needed. May be an injector stuck open..not sure it would have the effect you describe...but I'd disconnect one injector at a time and see what happens...at least the front 3 are easy to get at. Another way to check for that is install a fuel pressure gauge , start...let it idle until it dies...then check for pressure: it should stay near 40 psi for minutes. If it goes down within seconds, an injector is stuck opened.
Others might come with more ideas...
....check engine light ?????

[fordro]

I have not checked fuel pressure. All you can smell is gas when its running. I just changed the plugs and wires last night, and 2 coils. Funny thing is, it was running just fine after I did the coils then it went back to a sputter while acelerating. No where near as bad as it was before the tune up but never-the-less its still doing it. When I come to a stop, it bucks a little and acts like it wants to die. I watched the voltage gauge and it was low. dropping down to the last line before the "8" on the gauge.

I started to thinl it might be electrical. Some of the waring lights such as "ABS" and the "low oil light" flash and stay on when the van is OFF and nobodies in it. Checked the battery and it was only producing 294 CCA's and the Alternator pulley has a bearing noise. Could it be an electrical issue as well or something unrelated?

When it stops raining, I will put another battery in it and check the alternator amperage. Other then this, I am stumped. My next guess would be fuel but it seems to be getting plenty.

Thanks in Advance.

[LMP]

obviously you have your answer, and I should have suggested it: In fact, I just had the same problem, though I described it differently since I had immediately spotted the voltage problem before the sputter began...so no search except for why I had lost alternator...the exciter plug at the alternator had pulled off.....
http://www.automotiveforums.com/vbul....php?t=1062549

The GM alternator has frequent failures either at the voltage controller or the diode bridge, all built in the alternator but serviceable if you can handle a soldering gun, but test all external connections before.

[fordro]

I put a new battery in and tested the alternator. All was well. I finally figured it out. Cylinders 3 and 6 had a dead misfire. I started pulling the fuel injector plugs and found cylinders 3 and 6 were missing. The idle became better with them unplugged. Then I switched the coils around to see if the miss would change cylinders and it did not. So I bought an Ignition Control Module. Fixed that issue.

NOW, on to the final problem...

When I am driving, the transmission shifts as it should but when it hits 4th gear, it starts to shutter and when Overdrive is engaged, the whole van shakes and vibrates like its on a rumble strip or something. What would cause this? The transmission was rebuilt but no mention of any gear related things being replaced on the bill. Any help could be appreciated.

[LMP]

Originally Posted by fordro

...when it hits 4th gear, it starts to shutter and when Overdrive is engaged, the whole van shakes and vibrates like its on a rumble strip or something...

..4th gear IS overdrive. THe usual sequence is 3rd, then 3rd+TCC, then 4th(OD)+TCC....Slight tap on throttle will drop TCC and you are let in 4th(OD) until stable speed is attained and it gets back into 4th+TCC.

This is a frequent complaint....and I have this problem too ('93 3.8), though seemingly a little less severe than you describe, but I would use similar wording. My transmission is origin but mileage is near 100,000 miles only, and never abused.
GM says this is mostly caused by other causes than transmission, loose bushings, engine mounts, misfires, etc....
www.avigex.ca/xport/tccshudder.jpg
...but I think also the TCC clutch is the problem...except if it did slip, it should show as an RPM increase and pop a code...which do not happen . In fact, GM beefed up the TCC clutch a few years down the line, and that must mean something. FOr a test, I plan to pull the vacuum hose to the transmisison modulator...this will increase hydraulic pressure at normal throttle setting and want to see if it has any effect. www.avigex.ca/xport/modulator.jpg
ANother test is to pull one of the two TCC solenoid wires, either A or D...this inhibits TCC and would let you with a shooth drive....several forums members did so....at the expense of 400 or 500 rpm....and probably 1 or 2 mpg. BUt it is not clear that this corrects the cause or that it hides the effect....

www.avigex.ca/xport/tccconnector.jpg
www.avigex.ca/xport/transaxle.jpg

...to be continued....

[fordro]

Thanks for all the info. I am going to try the modulator here in a few minutes and see what that does. I have a receipt for transmission overhaul at 134,000 miles. The van currently has 214,000 miles on it. It might be possible the TCC clutch or converter is bad. Like I said, it shifts smooth and on time at any RPM up to OD, then once in overdrive, it shutters and vibrates.

Depending on the load I put on the engine, the shuttering can be light and almost un-noticeable or heavy and down right irritating at a moderate to large load on the engine while in overdrive.

[fordro]

I unplugged the modulator vacuum line and it shifted firmer and the shuttering in OD was not as pronounced as it was before but it was still there. I went ahead and plugged it back in for now until we can figure out exactly whats causing it to shutter. I just don't want to throw a bunch of cash at it.

[fordro]

Update***

I have consulted a few mechanics and have continued to look up the problem regarding the transmission shutter and have concluded its the torque converter. I have found a replacement one for about $125 new and plan to replace it next weekend. I can do a write up if needed. Thanks for you help LMP.

[LMP]

Keep us updated with pictures .....

[j cAT]

Originally Posted by fordro

Update***

I have consulted a few mechanics and have continued to look up the problem regarding the transmission shutter and have concluded its the torque converter. I have found a replacement one for about $125 new and plan to replace it next weekend. I can do a write up if needed. Thanks for you help LMP.

disable the TCC see if it is not shuttering.. if it is no longer an issue then the TCC is sticking. this can be in most cases worn..replacing this or disabling the TCC is next. if you use the vehicle under 4o- 50 MPG you will not see much MPG loss.

only get a new converter if it is the converter.

when this work is done flush out the tramsmisssion first then replace the filter fluid using the new dexron VI. do not use dexron III ......

[Jrs3800]

Just curious... How is it going to help him to disconnect the TCC for 4th operation with the shudder... I guess what I mean to ask is how is disabling the TCC for 4th TCC lock going to determine if the TCC is sticking?


A common problem with these is the TCC apply Valve bore, and not being able to hold the TCC as the pressure could be bleeding off.. This can cause a shudder in 3rd and 4th.. And can be viewed on a Scan Tool as TCC Slip RPM's...

I would love to see this van do a test drive with a Scan Tool to view the TCC slip when the shudder occurs... If the slip RPM's are low, say 0-40 or so then I would look elsewhere for the shudder.. Also how does the trans fluid look? Is it Red, Reddish Brown, Brown, Dark Brown or possibly Black ?

Does this shudder happen at all in 3rd gear? Or 4th gear only? And if its 4th gear only does it happen at all speeds or just heavy load situations?

[LMP]

Originally Posted by Jrs3800

...A common problem with these is the TCC apply Valve bore...This can cause a shudder in 3rd and 4th.. And can be viewed on a Scan Tool as TCC Slip RPM's..I would love .. with a Scan Tool to view the TCC slip when the shudder occurs...?

SO would I....There have been so many such cases in those forums....and never had someone come with a single identified fix or definite explanation solving the cause of the problem positively. IN fact, there are opposing facts. MIne DOES have the symptoms..GM says it is not the TCC...but it feels like it is, and I think you said the TCC was beefed up after '97 or so...however, I do "throttle up" in 3rd TCC and in 4th TCC just enough not to drop TCC...and the pull is hard, as this beef of 3.8 is able of doing, and I WOULD detect an actual slip and I have the feel and the ear for such if it happened...and damn, it pulls straight, solid, and yes, shuddering, worse in 4th for the lower RPM than in 3rd , but not a sign of RPM rise...except that going with the increase in actual speed; it acts as if the engine was bumping the mounts metal to metal , and yes, I can figure out this would be much more noticeable in TCC locked mode, and much less conspicuous in torque converter mode cushioning the piston strokes....as GM suggests...but I think the reaction torquing the engine/transmission unit againts its mounts would make that much more noticeable and easy to attain in 1st and 2nd gear...and it is not....baffling....
.... I can't convince myself to pull the transmission down to verify part after part without a cue....I'll go again after the engine mounts...just to convince myself ...
..mmm.. tell me more about the TCC apply Valve bore......and I would love a Scan Tool to view the TCC slip when the shudder occurs

[Jrs3800]

There were some changes for the valve body... Gm changed this several times over the years with The 4T60E.. supposedly 94 was Updated as well, but 95+ seems to be where its at... Thats not to say I have not seen the 91-93 units surpass 250,000 miles...

And then GM changed some of the internals for the 96+ 4T60E, overall these were the best of the 60E'e made..

The torque converter is a strange mix.. Some had a red fiber material for the clutch, but this would be an earlier unit with a straight on off TCC... Supposedly the PWM TCC used a Low Carbon Clutch and almost never burned up... I believe 96-97 was improved... The interesting part is that the older units could use the newer Carbon Converter, but the TCC apply would be a little more noticeable..

On the 94 Buick with the 4T60E he will have a PWM TCC apply... The apply can take as long as 7 seconds... But it will have to apply fully, or he can feel a shudder...

But here is my problem with this, Time and time again I have seen people diagnose a trans issue that was really an ignition issue... This is one of the reasons I would love to see the TCC slip when this happens.. Generally if it was that bad, he could throw a code for trans component slipping... But its hard to say..

He could even have a bad or burnt 4th clutches too.. There are just a lot of things that can cause a trans to slip..

[LMP]

Originally Posted by Jrs3800

...Time and time again I have seen people diagnose a trans issue that was really an ignition issue......if it was that bad, he could throw a code for trans component slipping.....

Thanks for the details. Indeed, no one ever mentioned a slip code with the symptoms, nor did I. ONe funny thing is I kept my TS in the garage for 3 months this winter, winter tires are mandatory for the winter season here and I have another car , and when I went back on the road, the symptoms were almost non existent....almost like the problem "cured" during inactivity, then came back slowly but surely. My '93 has the PWM...and I question this feature....wonder what would be the result if I tested a full ground on the B connector to PWM solenoid...
www.avigex.ca/xport/transaxle.jpg
...thus bypassing the modulation, and switching that "on the fly" only after TCC has applied....