2000 Yukon Surging when under lite acceleration

[Yukon2000]

Ok, this truck has been completely stumped on this 2000 Yukon 4x4 with 5.3 V8....anyone have any ideas...first let me say there are no codes in the computer...ran both engine and transmission codes, nothing.
Replaced, MAP, MAF, TPS, EGR, and did plugs and wires. Recently the intake was rebuilt with new gaskets and injector o rings. Fuel pump was replaced and fuel filter.

The scenario is this...the truck runs completely fine and revs up smooth and clean, idles great, no problems until put into gear. In gear it idles great with no issues...give it just a little gas with brake on and the tach will hit about 1100 when the motor will surge like it is dying out and trying recover over and over...will clear up once a little more gas is given...can hard brake it and rev under transmission load up to about 1300 and this problem goes away.

Also, when driving without doing this load test the truck will surge right after every shift under normal acceleration. However, hit the gas hard and the problem is almost compelte gone if not gone...hard wide open throttle and everything pulls great.

Any help would be great.

 

[clkelley]

Welcome to the neighborhood!

I would start with a couple of things, first, it could be your O2 sensors. They do not have to be throwing codes to be on their way out and they can cause tuning issues if they are on their way out. Also, during the maintenance, did you clean your throttle body?

Also, it may pay to take it to the dealer and have them "reflash" the ECM. I know it sounds simple, but with all the changes you have made, the signals to the ECM from the sensors could cause some running issues, if the ECM needs to be reflashed.

Anyway, just suggestions really, to get you started.

 

[Yukon2000]

I did forget those items...sorry. The ECM was just reflashed and the dealer also ran a full diagnostics and did not get any codes or even out of range reports. The entire intake and the throttle body was completely cleaned and even a new idle air control was put on it. The only thing I have not done is the O2 sensors but again it really drives me nuts that it is not throwing a code so it is hard to keep buying more parts even though that has been the only options so far while trying to work through this thing. Also, should note the problem noted originally occurs no matter the temperture outside or of the motor. Also, did even go through a test on the transmission to make sure it was not a TCC issue and no issues there since the transmission was rebuilt about 6 months before this started.

Thanks for the input and I will take the O2 sensors into account and will go look at them more but anything else would be very helpful.

 

[tonymac617]

Shift soleinoids? TechII should be able to test them if they werent part of the transmission test you recently had done.

 

[clkelley]

Have you done all the work yourself? Have you put a data logger on it at all? Tech II or EFI Live?

 

[Yukon2000]

For both the tranmission question and the testing question related to me doing it myself...It has been both to the tranmission shop that rebuilt the transmission about 2 years ago and the dealer for full diagnotics of which neither report anything but the MAF sensor was reporting low out of range...the MAF was replaced. Still the issue continues.

Just as an update...went crazy this weekend and went through and disconnected the O2 sensors to see what reaction I would get from the system. No CEL with them disconnected and the truck ran exactly the same as my original post...lite accelleration and surges...hard on the gas and it runs great. Also shift points caused surging too.

Thanks again everyone for the pointers but I am still not sure where this issue is because it sounds like everything has been checked. About to jack it up and put a new one under it but hate too...it has been too good of a truck up to this point.

On the O2 sensors being disconnected, should those not throw a code?? Never got one even drove it for about 20 minutes...did not want to trash the cat which can happen in some cases if the O2s are doing their job.

 

[tonymac617]

When did the surging start? was there any action that caused the surging? Recent work, etc? This ones got me stumped too!

 

[clkelley]

The O2 sensors should throw a code. Did you replace the MAF just once? I have actually seen them come from the manufacturer bad. DO you by chance have an aftermarket intake and if so what kind?

 

[Yukon2000]

The transmission was rebuilt about two years ago and no issues for that long and then the only thing that was done was the intake manifold gaskets becuase a water leak was found in the tubes under the manifold. That is all that was done but again as mentioned up above that has been gone back through at least 10 times...everything has been replaced on the manifold including a new manifold, the plastic part. New injectors were also put into place, dealer versions. This issue started very shortly after this manifold gasket change but again many checks have been done on it and everythign looks good there plus it ran good for about a week after this change.

Thanks for the questions and input.

 

[Yukon2000]

On the MAF input...that is interesting. I did replace it with an aftermarket one...however we elimenated that by pulling one from another well running truck and same issues...also put the MAF we bought into that truck and no issues.

Regarding the O2 sensors...decided to try something crazy...unplugged the front one on the drivers side and started it and tested, same results. Unplugged the front passenger side and same results from the test. Then unplugged the after cat ones and same results. So, went one crazier step and pulled all four plugs on the O2s. Same results during the tests but one major note...NEVER SAW ANY CODES with the O2s completely unplugged. I would have thought we would have seen the codes at least and also would have had some performance issues but in the drives around the block nothing worth noting other than the surging. I am wondering now if this could be the issue...the O2s being disconnected should have caused some change, right???

 

[Drivinmenuts]

Wondering if Yukon2000 had made any progress on his surging problem. I have a 2000 Tahoe doing the exact same thing. Only seems to happen after torque converter is locked up, surges around 1300 rpm lite throtttle. It will cruise fine but the second I apply a little more throttle, the rpm go up for a second like it wants to move then they drop, then it chugs until I give it enough throttle to downshift into third. If its chugging, I tap the brake to unlock the converter it also does fine. Just did a ride along scan and had no apparent problems and is throwing no codes. Replaced fuel filter, did full fuel injection de carb including throttle body, and new plug wires. Plugs were done 10000 mi ago. I did notice that the upstream 02 sensor is rattling inside, maybe that's it. Dunno. Ideas?

 

[Yukon2000]

Man you do not know how bad this thing is reconfigure me nuts....changed all O2s and still same issue. I went so far as to put the transmission into manual mode by pulling power and same thing. But your right seems to be related to torque converter lock and light acceleration. Get in it and this thing runs like a champ. I have no ideas and had the computer checked again at the dealer and asked them to flash a second time...no luck again. I am starting to think mechanical with cam timing or something....timing chain jump maybe???? Have no ideas other than that. ANYONE HELP??????

 

[Drivinmenuts]

I'm leaning towards fuel/air or ignition. Maybe a bad coil pack. Is there a way to test those? And if one was going bad would it throw a code. My computer had 512 misfire counts but who knows when those happened. Not getting realtime misfires with scan tool hooked up when truck is surging. Did u find out why u weren't getting codes after u ran without o2 sensors?

 

[Drivinmenuts]

Maybe try with a scan tool to see what yout throttle position sensor output is when your truck is surging. The voltage should be steady. I did this test on mine and it passed, but maybe could try that. U could do that at a parts store, no need to go to dealer.

 

[Yukon2000]

Yeah I have replaced the TPS already thinkingng the same thing. No joy. I agree that it seems to be fuel air mixture but something is telling wrong mixture or something. I went down this path with it and did a MAP, MAF, TPS, idle air control, even a new intake manifold and gaskets, new EGR, fuel filter, fuel pump, plugs wires, and even did cam and crank sensors. I am just about out of sensors....thinking on the O2s because it is about the only I have not done. Unless like I said mechanical??? Oh and did a compression check all were within specs and actually within just a few pounds of each other probably tolerences of the guage. Anyway will be interested drivemenuts, if your O2 being replaced might fix it. Are replacing the one rattling one???

 

[Yukon2000]

BTW, it appears I did not run it long enough with the O2s off...that might be the case as it appears they will be declared, log a code, bad after a period of time, not sure how long or after so many tests by the computer. We only ran it down the street and back...then plugged them back in.

 

[Yukon2000]

Sorry about three replies...I have not had any misdirected codes at all on this thing.

 

[Drivinmenuts]

I haven't replaced the o2 sensors yet. I've heard that even though they rattle on the inside sometimes they still work. The tech from the GM dealer didn't notice the sensors acting up, but who knows what he was looking at while I was driving to replicate the problem. I didn't discover the rattle until I had left the dealership. I know the o2 sensors are a little pricy so that's why I've held off. I hate throwing money at sensors just to jump in the car all excited after replacing it and still have the problem. BEEN THERE! On Monday i will ask the opinion of the dealer about the broken o2 sensor and I will be sure to let you know if I make any progress. How is your gas mileage?. I'm at 12 city and 14 highway, which seems a little low. Thanks for responding.

 

[Yukon2000]

Just curious if you got any news on your visit back to the dealer? Still have not done the O2s but let me tell ya I have been a GM guy for a very long time and never had one like this...about to tell the dealer I am buying a Ford.

 

[Yukon2000]

Ok, here is an update...as I posted orginally I did not have any codes on this thing for all the issues I am fighting so it became a symptom based troubleshooting replacing the parts. This weekend took and disconnected the transmission main wiring harness...still an issue. Plugged it back in and drove it a around a bit. No codes same issues with orginally noted. Came back and again unplugged the transmission again of course lots of codes but drove it around the block in fail safe mode for the tranny. Acted very similar but slightly different in that the bucking was always there and the same.

Replugged in the tranny and cleaned all the connections on the tranny which is not easy in the truck but cleaned it up real good. Cleared all codes on the computer. Then drove it around...the thing threw a SES and also an ABS and brake light. Wierd...pulled the codes again and got the P0742 code and while driving got a code for the wheel speed sensor, forget the code. Went through the connected reseat again and with codes cleared and drove again...same codes.

So, went ahead and took the truck to the tranny shop this morning...they found the issue...bad TCC solenoid, and a bad wire in the tranny. They are replacing now and looks like we might have a fix...the wire shorting was the big issue and also the bad connection on the connector which the tranny shop is also replacing. Looks like the connector was a bit over heated from being right next to the cat.

Will update with the final outcome after the tranny fixes. This drove me nuts but this is the best thing I have seen...never thought I would be happy to see a code on a truck.