6.0 Swap Stumbling Idle

[Rich84]

I have a 2004 Van 6.0 that I put in a 1986 longbed..Idles smooth until you rev the motor. As it decreases idle it stumbles as it idles down.
Exhaust is a little leaky it is just kind of patched together so I can get it to the exhaust shop.
It has 2 codes 135, and 155 for the o2 sensors. If I unplug the MAF it runs and idles perfectly.
Is this happening because of the small leaks in the exhaust? Vacuum leak?

[LeesTruk]

Rich, those codes are heater circuit codes for your O2 sensors. One or both sensors may be bad. Do you have a scan tool that'll give you live data? Unplugging your MAF sensor puts the PCM into a speed density mode (I'm pretty sure) so the PCM may not "look" at the O2s for fuel scheduling purposes

[Rich84]

Do you think there is a good chance that both brand new Bosch sensors are bad out of the box? I did check the fuse for the heater circuit and it is good. I am going to recheck all my grounds to make sure everything is OK.
Any other suggestions would be appreciated.

[Wildkarde]

Those are codes for bank 1 and 2 02 heater circuits. Most likely they aren't being either grounded or fed a power. 2004 would have grounds coming from the PCm most likely, though vans did some wierd stuff. Check and make sure the pink wire in the 02 connectors has power when the key is on.

[truckdude239]

I have never had good luck with bosch sensor i always stick to denso or ac delo for gms

[BR3W CITY]

Are you using a reworked harness, or is it an aftermarket one? The aftermarket harnesses often use a different style plug and matching sensor. The most common one being used was the Bosch 13444. There are other o2 part #'s that will fit that plug but have the incorrect heater circuit wiring, or no heater at all.

You mention new sensors, which part # are they?

[Rich84]

It is a new harness from fuel injection connection. I have had good luck with their harnesses in the past. It’s a Bosch 15284 that he recommends. It does go closed loop and seems to run pretty good but I have not taken it on the road yet. I got the air intake system ironed out so I can rule out any ummtered air getting past the MAF. I suspect a vacuum leak because I also threw a lien code for both banks. I had received this code when the motor was still running in my van.

[BR3W CITY]

Originally Posted by Rich84

It is a new harness from fuel injection connection. I have had good luck with their harnesses in the past. It’s a Bosch 15284 that he recommends. It does go closed loop and seems to run pretty good but I have not taken it on the road yet. I got the air intake system ironed out so I can rule out any ummtered air getting past the MAF. I suspect a vacuum leak because I also threw a lien code for both banks. I had received this code when the motor was still running in my van.

Yea thats who did my harness, tho he had me use the other sensor I mentioned. His harnesses are good so I don't suspect an issue there.

[Rich84]

So I was able to spend a little time with the truck this weekend. The idle seems to have smoothed out a bit. I wonder if there may have been a sticky injector or two. I am still getting the Heater circuit code on the 02 sensors. Probably will end up trying 2 new ones. I will test the pink wire first as stated above. The exhaust is extremely leaky, but that would not have anything to do with theses codes..Correct?

[Trackman101]

Your O2's will be fine. You have to find the wiring issue.

[Rich84]

I got the exhaust buttoned and drove the truck about 40 miles. It ran really strong but it smells a little rich. It still has the heater circuit codes but it does go into closed loop. This weekend I will double check the grounds and test for power.
On a side note the 273's in the rear are going to have to go. 65 MPH it is at 1400 on the tach, and it is going in and out of OD constantly around town. Thinking back Robert at FIC did not ask me about the gearing in my rearend. So my speedometer is off about 30%. The van had 373's. I am using a ScanGauge for a speedo.

[Wildkarde]

You can usually smell a little fuel in the exhaust if you arent running cats.

And if your tuner didnt ask for gearing/tire size then the trans is never going to really shift well. You need to have the vehicle speed somewhat close in the computer as speed is what determines when the thrans shifts for part throttle.

[davepl]

If the exhaust leak is upstream of or not far downstream of the O2 sensor it'll not work well at all. O2 sensors read the amount of oxygen left, as you likely know, and fresh air has a ton, so it'll be all out of whack.

You can't run an O2 sensor in a leaky exhaust. Well you can, but it's useless.

[Rich84]

The exhaust has been fixed. No more leaks.
My tuner says that for some reason the PCM is not "seeing" the 12 volts at the o2 heaters..He has to program out the code.
Looks like I will be shipping out my computer.

Is there any reason that the truck would stumble quite a bit in reverse? It almost feels like it wants to stall. Pop it into neutral and it smooths out. It does not run like that at any other time.

[87chevy.com]

Probably best to wire test the sensor and harness to make sure there isn't a problem turning off a code isn't the right way to go about it unless it's say something you deleted from the harness..

[Rich84]

I have to ask this question again..The problem persists.

Is there any reason that the truck would stumble quite a bit in reverse? It almost feels like it wants to stall. Pop it into neutral and it smooths out. It does not run like that at any other time.

I am getting a PO101 MAF code. I have tried 4 different MAF sensors. I have also replaced the intake gaskets. Also, When cruising at light to medium acceleration there is an occasional momentary hesitation. It almost feels like a misfire. It is for a split second. Seems to happen randomly.

Thanks for your help.

[Trackman101]

Are the O2's working now?

[Rich84]

The O2s appear to be functioning properly. The pcm goes into closed loop quickly. My tuner was not concerned with the heater circuit issue. He made it sound like it was throwing a code due to something he did or did not do with the tune.

Is it correct that the heater circuits are most important at startup to get the system into closed loop quickly ?

[BR3W CITY]

Originally Posted by Rich84

I have to ask this question again..The problem persists.

Is there any reason that the truck would stumble quite a bit in reverse? It almost feels like it wants to stall. Pop it into neutral and it smooths out. It does not run like that at any other time.

I am getting a PO101 MAF code. I have tried 4 different MAF sensors. I have also replaced the intake gaskets. Also, When cruising at light to medium acceleration there is an occasional momentary hesitation. It almost feels like a misfire. It is for a split second. Seems to happen randomly.

Thanks for your help.

If your in neutral and you pop it into drive, does it bog, or is it ONLY in reverse? Did you try the hitting it with starting fluid and looking for idle spikes? There are a few places on the intake (at TB, at EVAP solenoid) that can have annoying leaks, or there is the potential of a cracked intake.

If the tuner you work with has been decent, ask if he'll log the ecm for a short drive. The hesitation you describe would show up on the log and let you determine if its related to a specific context.

[Rich84]

It only runs rough in reverse..Like the idle is to low and I can hear the tensioner making noise.
I have looked for leaks. I replaced the intake with another and checked for leaks at the locations you mentioned. I'm pretty confident there is no leaks at this time.

I don't really have a tuner. Robert from FIC did the programing when I bought the harness from him. So I am on my own.

[Rich84]

I have put about 1500 miles on it so far. I have had to top off the radiator and overflow bottle a couple times. It has taken almost an additional 3/4 of a gallon of Dex-Cool. Looked last night after about a 40 mile trip and the bottle is down another 1/2 inch. No smoke. It's not overheating. Still running rough in reverse when it's at full temp. Still has trouble with warm starts. Starts right up when cold.
I have other things I want to do to this truck, but not if I have to rip the engine apart first.

[Rich84]

Wow that was a quick 2 years..

So I did finally figure out what was going on. The MAF readings were all over the place . The IAT was reading about 30* too cold. I could not find a vacuum leak because i wasn't looking in the right place. I kept checking the intake and found nothing. The throttlebody itself was leaking out around the linkage. The gasket was fine.

So one new MAF and a new throttlebody and she is running like a champ.