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2004 Sonoma ZR5 SLS crew cab 4.3 4x4
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Discussion Starter · #1 ·
Hi all, new to the forum. I just got a new-to-me Sonoma a couple weeks ago. It’s a 4.3 4X4 crew cab ZR5 with 136k. I’m having an issue with the driveline. Between 1300 and 2000 rpm I’m getting a repeating 200-500 rpm surge when maintaining speed or mild acceleration. This happens at most any speed that I’ve noticed matches that rpm range (45-70 mph). I haven’t noticed it below 40 ish and haven’t driven faster than 80ish. The tach will gain for about a second then lose for about a second and continue this pattern till I have to decelerate or it’s no longer in the rpm range. I tried driving in 3 and it didn’t seem to make a difference. The CEL is not on. It’s an often but intermittent problem. Sometimes it doesn’t happen, but when it does happen, it’s just about constant. it almost seems like a dice roll at start-up. Other than that, it runs very smoothly. Any help or insight on where to start or how to fix this would be greatly appreciated. Thanks in advance!
 

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I'd look over all the vacuum hoses under the hood. There is number of them right in front of the master cylinder.
Wouldn't hurt to put a scanner that can read transmission codes on it.
 
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year stated in his avatar
cool, now knowing he has a 98 up S truck, every single PID in his computer is fully scannable to see 100% exactly what's going on.
Now, he just needs to A either get a scanner, or B go find someone with a scanner and report back with what was found.
 

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91 base=driver, 94 mid engine=build
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Most auto parts will scan for free. You can also rent a fuel pressure tester for next to free/free when you return it.

I would check my compression (you can rent that tool also) if the codes and fuel pressure did not reveal anything.
 

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2004 Sonoma ZR5 SLS crew cab 4.3 4x4
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Discussion Starter · #7 ·
Wow! Thanks very much everyone. I’ve got plans to get HPTuner software but till then I’ll stop by local parts shop to borrow a more capable scanner than the basic one I own. Thanks again I’ll report back with what I find out.
 

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2004 Sonoma ZR5 SLS crew cab 4.3 4x4
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Discussion Starter · #9 ·
Sorry for the late response life has gotten in the way again lately. I’m a little embarrassed to admit this but it was the transmission fluid level was a couple or so quarts low. Maybe someone had replaced the trans filter and missed filling it back up or did partially? Not sure. Either way, I have learned the proper way of checking trans fluid levels and this community is an extremely great bunch of people. Thanks again.
 

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2003 Sonoma SLS ext. cab 4.3L / 4x4
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Sorry for the late response life has gotten in the way again lately. I’m a little embarrassed to admit this but it was the transmission fluid level was a couple or so quarts low. Maybe someone had replaced the trans filter and missed filling it back up or did partially? Not sure. Either way, I have learned the proper way of checking trans fluid levels and this community is an extremely great bunch of people. Thanks again.
Since the truck is relatively 'new to you', you may not have a way to verify how long the tranny was low on fluid, nor under what conditions it was subject to. It would be a good idea to check on it regularly to make sure it all seems to be operating normally and holds a consistent fluid level. Have you checked to make sure that the tranny isn't leaking (like @ the seals/ gaskets)? What color is the fluid at present, and does it have any 'burnt' smell to it?
 

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Sorry for the late response life has gotten in the way again lately. I’m a little embarrassed to admit this but it was the transmission fluid level was a couple or so quarts low. Maybe someone had replaced the trans filter and missed filling it back up or did partially? Not sure. Either way, I have learned the proper way of checking trans fluid levels and this community is an extremely great bunch of people. Thanks again.
Hope it's not toast !
 

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Most auto parts will scan for free.
reading stored codes is NOT scanning or datalogging a vehicle.
Actually hooking up a scanner, and go driving 30 miles, and then having the file of every portion of the drive from start to finish is scanning. To know when the TW conbverotr is locked or unlocked, and howmuch actual slippage is from the engine and the output shaft is crucial for ID'ing slipping, and at what %the tps is when slips occur, what pressure the trans is running at, there is so much i could keep going on with ushc as how much air the engine is eating comparing to what the computer thinks it is eating...no parts store can tell you any of that.
 

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2004 Sonoma ZR5 SLS crew cab 4.3 4x4
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Discussion Starter · #14 ·
I’ll certainly be checking it regularly from now on. The fluid looks pink and doesn’t smell bad/burnt. The problem hasn’t reoccurred since I brought the level to within spec. Maybe dodged a bullet this time but will definitely keep an eye on it. I really appreciate all the info and pointers from this great community.
 
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