97 stumbles when cruising

[Kevin Callahan]

I had this almost exact thing happening to my Yukon. Do you still have the stock plastic distributor? I replaced mine with a Summit Racing one and the stumble at cruising is gone.
The gear on the original one was sharp and pointy like a knife edge, not square like new. I went under the hood to wiggle the spark plug wires at the distributor cap and the whole thing lifted up. One of the screw bosses on the plastic distributor was broken and cap was only holding on with one screw.

Vortec Distributors SUM-850098​

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As far as I know the distributor is stock but mine is aluminum with a plastic cap. Had the distributor out last year for a misfire problem and thought it was the gear. It looked like new still. Oil has always looked good so I don't think it's tore up the gear in that time

 

[Schurkey]

My 97 tahoe with the 5.7 vortec

As far as I know the distributor is stock but mine is aluminum

If it's aluminum, it's not stock.

 

[Kevin Callahan]

If it's aluminum, it's not stock.

I've never seen a plastic distributor in these. I didn't know that was a thing. Every vortec I've owned had an aluminum. All must have been swapped at some point before me owning them

 

[paule1192]

Sonnax 77754-04K TCC Regulator Valve & Isolator Sleeve Kit , 4L60E 4L65E 4L70E | eBay

This is a primary cause for TCC-related slip code P1870 and overheated converters. Exhausting apply pressure also diminishes line pressure, which can result in burnt clutches. Excess wear at the isolator valve bore reduces TCC apply pressure.

www.ebay.com

Sonnax 77754-R2 TCC Regulater Valve Reamer Tool 4L60E 4L65E 4L70E 4L70 | eBay

Depth Guard to prevent over boring.

www.ebay.com

I can almost promise you this is your issue, I spent months chasing this issue down and no one ever talks about this unless you look specifically at the transmission. The valve in this wears the edge of the valve body down until fluid can get past it and then it can't lock up at cruising speeds. You have to slowly ream it out with a special bit and a rachet, but if you put this in you will be able to lock up again. Make sure you clean the metal shavings out with some transmission fluid before installing the sleeve.

I also did these upgrades to the valve body when I was in there:

Transgo 4L60E SHIFT KIT & Valve Body Separator Plate combo 1996-2000 (21600)* | eBay

TRANSGO SHIFT KIT. TRANSGO VALVE BODY SEPARATOR PLATE. With the 4L60E 4L65E 4L70E 4L75E Transmissions. light & Hard 1-2 shift. Has new design Isolator Valve that works perfect in worn. _______ A Must to remove code 1870 _______.

www.ebay.com

TransGo 2nd Gear Heavy Duty Aluminum Accumulator Piston--Fits 4L60E Transmission | eBay

TransGo--Heavy Duty--Aluminum--Accumulator Piston & Seal--With Legs. TransGo 2nd gear accumulator piston. 4L60E & 4L70E series parts in. Fits accumulator housing with casting. Made of high grade aluminum.

www.ebay.com

Transgo 4L6-FWD 4L60E 4L65E Aluminum Forward Accumulator Piston 93-09 Heavy Duty | eBay

Fits all 4L60E, 4L65E, 4L70E, 4L75E 93-on. Forward Accumulator Piston. Replaces both plastic and aluminum that prematurely break and wear out.

www.ebay.com

I also replaced all the solenoids while I was down there.

I had never touched a transmission/valve body before and this was pretty easy and I have had zero issues, just be meticulous and don't forget the O-ring on the accumulator valve or you get to take it all back apart .

P.S. My transmission had been rebuilt about 50k before this too so don't let that sway you.

 

[Kevin Callahan]

Sonnax 77754-04K TCC Regulator Valve & Isolator Sleeve Kit , 4L60E 4L65E 4L70E | eBay

This is a primary cause for TCC-related slip code P1870 and overheated converters. Exhausting apply pressure also diminishes line pressure, which can result in burnt clutches. Excess wear at the isolator valve bore reduces TCC apply pressure.

www.ebay.com

Sonnax 77754-R2 TCC Regulater Valve Reamer Tool 4L60E 4L65E 4L70E 4L70 | eBay

Depth Guard to prevent over boring.

www.ebay.com

I can almost promise you this is your issue, I spent months chasing this issue down and no one ever talks about this unless you look specifically at the transmission. The valve in this wears the edge of the valve body down until fluid can get past it and then it can't lock up at cruising speeds. You have to slowly ream it out with a special bit and a rachet, but if you put this in you will be able to lock up again. Make sure you clean the metal shavings out with some transmission fluid before installing the sleeve.

I also did these upgrades to the valve body when I was in there:

Transgo 4L60E SHIFT KIT & Valve Body Separator Plate combo 1996-2000 (21600)* | eBay

TRANSGO SHIFT KIT. TRANSGO VALVE BODY SEPARATOR PLATE. With the 4L60E 4L65E 4L70E 4L75E Transmissions. light & Hard 1-2 shift. Has new design Isolator Valve that works perfect in worn. _______ A Must to remove code 1870 _______.

www.ebay.com

TransGo 2nd Gear Heavy Duty Aluminum Accumulator Piston--Fits 4L60E Transmission | eBay

TransGo--Heavy Duty--Aluminum--Accumulator Piston & Seal--With Legs. TransGo 2nd gear accumulator piston. 4L60E & 4L70E series parts in. Fits accumulator housing with casting. Made of high grade aluminum.

www.ebay.com

Transgo 4L6-FWD 4L60E 4L65E Aluminum Forward Accumulator Piston 93-09 Heavy Duty | eBay

Fits all 4L60E, 4L65E, 4L70E, 4L75E 93-on. Forward Accumulator Piston. Replaces both plastic and aluminum that prematurely break and wear out.

www.ebay.com

I also replaced all the solenoids while I was down there.

I had never touched a transmission/valve body before and this was pretty easy and I have had zero issues, just be meticulous and don't forget the O-ring on the accumulator valve or you get to take it all back apart .

P.S. My transmission had been rebuilt about 50k before this too so don't let that sway you.

I ordered a scanner that will tell me if the torque converter is locking up or not. If it isn't this is definitely something I'll look at

 

[SableSlayer]

What are your long term fuel trims looking like?

 

[Kevin Callahan]

What are your long term fuel trims looking like?

I will have to double check but I believe over the weekend they were -.4 or something like that. Both sides were comparable

 

[Kevin Callahan]

Been a while but have an update. After getting the new scan tool the Tahoe has been running great making it hard to track down problems. That is until today. This afternoon it started to run extremely rough and threw a p1345 code. Is there a way to test the cam and crank position sensors? They are both only a few years old but I'd like to check them. The Tahoe has 208k on it and what I've read said if not the sensors then it could be distributor or timing chain. Anyone have any advice for ways to test before I pull the distributor to make sure it's in good shape

 

[WICruiser-97]

If the problem comes and goes it is not likely a sensor as they tend to fail and not recover. Distributor gear wear could easily cause the p1345 code as the range is +/- 2 degrees. However, the code and the problem may not be related.

 

[Kevin Callahan]

If the problem comes and goes it is not likely a sensor as they tend to fail and not recover. Distributor gear wear could easily cause the p1345 code as the range is +/- 2 degrees. However, the code and the problem may not be related.

It now runs like timing us out but only once it's warm. Runs fine cold. Distributor was out last year and looked like new and according to scan tool is set at 0 like it should be