Huge hesitation, mechanically inclined. Please help

[Chip18]

You can check just about every sensor with a DVOM, you just need to know what the values are?? And dare I say it but a Chilton and or Haynes manual should have that info. And yes you can use carb spray to check for a vacume leak and go ahead and hook up a vacume gauge anyway to see what the motor is doing at idle??

The one sensor I did not see you mention?? Is the IAC ... Idle Air Control motor/valve?? It could have carbon build up on it???

Some info on it

http://www.gmtuners.com/tech/TPS_IAC.htm

Some info on it, if they ran a scan they may still have the data?? Seems like it's a fairly rare failure however?? Looks like it's about a $50 part?? Couldn't hurt to pull it and clean it in anycase.

 

[Brian Wilson]

You guys have been a ton of help. Very Informative member base in this forum.

 

[Brian Wilson]

In other news I finally got a check engine light so my fingers are crossed

 

[02Lightning]

The one sensor I did not see you mention?? Is the IAC ... Idle Air Control motor/valve?? It could have carbon build up on it???
QUOTE]

I didn't think drive by wire cars had a idle air control valve?

 

[Chip18]

http://repairdata.cnlaunch.com/pdf/2013/09/25/91ba623e-0f70-4621-9342-f4c7d469e48a.pdf

I had to edit my original post cause I left out a word.

That is what I found and my buddy at the dealer said the same thing. I'll be driving and all the electronics will shut off and come right back on. The motor has shut off once that I can positively remember. I have a code reader and it throws both the codes in the link. I have replaced the main fuse and and cleaned the easy terminals. I'm thinking next is battery and alternator cables.


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That is seriously messed up!

I didn't think drive by wire cars had a idle air control valve?

LOL ... I'm going off of concepts of operation of Fuel Injected motors in "general."

I'm certainly "Not" an expert on these motors. An IAC is listed as a replacement part but I have seen T-Belt kits for "Nissans" and "Nissans" ... have "Chains" ... not belts, so there is that.

I'm sure one of the "Chevy Gurus" will confirm if these motors have IAC's.

And ... you have a 02 Lighting??? Awesome Trucks, we have a couple out here ... they only show up in the summer time!

 

[Rocket Man]

@Chip18

 

[Tonyrodz]

Lol!!

 

[Chip18]

@Chip18

I don't get it???

 

[Brian Wilson]

Ok, so after all day testing with a snap on modulus 2 and a tech 2, my car is perfectly fine. Absolute 0 problems. BUT, it still hesitating like crazy. All sensors are working correctly and throttle body is not sticking. The only fault I could find is at certain times, the timing would drop to almost 30 degrees retarded. The timing was all over the place. I know the cam position sensor and knock sensors are working correctly. What else can anyone thing of that would retard my timing?

 

[Chip18]

There is also a "Crank Position Sensor," it's job is to determine TDC. If it's off ... it could be sending the wrong info to the "Knock Sensor" whose job it is to "Pull Timing."

 

[iamdub]

You said you finally got a CEL- what was the code(s)? When a code is set, you can get a freeze frame for it with better scan tools, especially a Modulus and TechII. A freeze frame is highly valuable to diagnosing issues such as this.

 

[Brian Wilson]

Unfortunately the CEL was just a p442 evaporated code

 

[Brian Wilson]

I believe we tested the crank sensor as well

 

[Chip18]

OK all those sensors "should" be good then?? Still it would not hurt to check then with a DVOM meter. On my 951 (Porsche 944 turbo S) I refused to belive my newly installed Fuel Pressure gauge that kept reading 0??? Despite the fact that I had installed not one but two new fuel pumps???

Finally I stuck the new fuel pump in a freakin gas can with hoses on the end in and out applied 12 volts ... despite the fact that I could heard the pmp running ... it did nothing???

Just cause the part is "new" does not necessarily mean it works ... apparently???

 

[Brian Wilson]

FIGURED OUT THE PROBLEM!!!
kinda...
Alittle history I assumed was unrelated. I had a brake caliper dragging awhile back on passenger side front. So I replaced it, replaced pads and rotor on both sides and vacume bleed them. The next day it locked up again. So I replaced the flex hose going to the caliper and vacume bleed it. I thought the problem was fixed. This was months ago. Today I jacked the front end up to pull the front differential out to check it out inside. I noticed the passenger side wheel had alot of drag on it when I leaned on it. So I open the bleeder valve and it had pressure. Fed up with it, I replaced both front calipers, pads, rotors again. This time I used a snap on modis 2 auto bleed program to bleed each wheel. Well, my master cylinder decided to go out during the process so I bought a new one. All components used this time were brand new, not remanufactured. Installed and auto bleed again. Thought everything was great. Drove about 2 miles. And noticed the brakes were dragging ALOT. Cracked the bleeder on both front brakes and had pressure. Then drove the truck 21 miles home with no issues and absolutely no hesitation for the majority of the trip. And when I got home just for shit and giggles, I feel the wheels and they are hotter than they should be. Cracked bleeders, pressure but not near as much. Also noticed my pedal feels soft when I first let pressure out but as I use brakes driving, the pedal gets more firm.

So, long story short, brakes dragging was my entire problem that I have been having. Now the problem is why do they keep holding pressure? Brand new master cylinder and calipers and rubber hoses. So it must be in the brake booster or abs pump assembly?

 

[Rocket Man]

Nice to know the cause of the problem, now on to the solution. And I have no ideas as of yet to why that would be happening. Do you have Hydroboost?

 

[Brian Wilson]

I don't know. It's all stock

 

[Chip18]

Ok ... that sounds "Seriously Messed Up" so to be clear ... not an "Engine Issue" then???

 

[Brian Wilson]

It was not an engine problem. I don't have hydroboost. Also, this looks like a very common problem on newer gmc trucks. Most people say pulling the abs fuse fixes the problem. A few say bad brake booster will cause it. I also noticed the rod going thru the firewall to push the master cylinder piston is adjustable. I might need to adjust it in a bit if it is holding pressure on the piston.

 

[Chip18]

Ugh ... "speculating here" and considering the timing being pulled thing??? PCM would be cutting power "Traction Control" so the "PCM" thinks the vehicle is outa control. So that kinda makes sense, disabling ABS is a work around but obviously ... not ideal.

Maybe you have a bad brake line???