Swap Startup: Stumbling
 

I am done with my swap and have asked a lot of questions on here that have helped me along the way so I appreciate the help. This is hopefully my last issue to resolve. The motor stumbles when I press the accelerator and acts like it doesn't know what to do. We hooked a scan gun to it and 1. it says I have a 5.3L 4x4 ECU and 2. it shows a low MAF reading. I swapped out the MAF and that didn't change anything. It is in the stock Silverado location by the airbox as well. I also called BP Automotive who flashed my computer and they said that they flashed it for a 4.8L per the detail I sent them. Any thoughts/things to test?

Side note, I can't actually drive the vehicle until my tires come in as the wheel are too small to clear my suspension.

Re: Swap Startup: Stumbling
 

I may have a vacuum leak as well, I only have 3 vacuum lines connected and from some research it seems there may be more ports than this?

1. Large Rear Nipple - to brake booster
2. Medium Top Nipple - to PCV (this one was already hooked up)
3. Small Side Nipple - to fuel pressure regulator

Re: Swap Startup: Stumbling
 

After fiddling with the MAF for awhile, we pulled the TPS connector off and it ran better and has throttle response. Perhaps this sensor is bad.

Re: Swap Startup: Stumbling
 

Same issue with mine. TPS was the problem. Hopefully this will get you on the road!

Re: Swap Startup: Stumbling
 

The new TPS didn't resolve the issue. I have no codes either. Currently the VSS is unhooked, could this cause stumbling under acceleration?

With the TPS unhooked it can be limped but wants to stall at idle.
With the TPS hooked up, if you press the gas it stumbles badly and does not want to accelerate.

Re: Swap Startup: Stumbling
 

Did you try running it just with the entire MAF unplugged? It should force fail into the VE tables and be able to idle and rev without too much issue.

Re: Swap Startup: Stumbling
 

So the truck stumbles when the MAF is connected but runs good when you disconnect it?
I had the same problem it turned out that to be the intake tube I was using was larger then original so it was getting more air than it thought. I had a spectra cold air intake and the kit I had didn’t have the plastic reducer that fit in the tube around the MAF. As soon as I put that in it ran fine.
What intake are you using? What MAF?

Re: Swap Startup: Stumbling
 

It runs ok when the TPS is unhooked and stumbles when it is hooked up. I tried hooking up the TPS and unhooking the MAF and it just surged over and over (revved up dropped off repeatedly). I am using the stock Silverado intake and MAF.

Re: Swap Startup: Stumbling
 

It actually seems to be running better now with TPS unhooked almost no noticeable issues unless you come off the throttle hard it will die. Not sure why it runs like crap with the TPS hooked up.

Re: Swap Startup: Stumbling
 

Do you have a scanner so that you can actually watch what the TPS is reading?

Re: Swap Startup: Stumbling
 

I don't what kind of scanner would I need for this (assuming more than a normal OBDII scanner)? My fans are not getting any ground either so I would like to activate those as well but may need more than a scanner to do this.

Re: Swap Startup: Stumbling
 

I got a scanner and took these readings, curious as to the difference in the O2 readings but honestly don't know what this is telling me. Also, using OBD Fusion I am not sure what I am looking for to read the TPS. The truck runs pretty good with the TPS unplugged but when I plug it in, it surges and loses power repeatedly like if you dumped the clutch with no throttle.

Re: Swap Startup: Stumbling
 

MAP reading was 10.63 inHg at idle, 02 Bank 1 was 0.93V and 02 Bank 2 was 0.44V. MAF ranged from 0.75lb/min to 1.0 lb/min in the 600 to 700 rpm range, respectively. I have 2 MAF's (junkyard) and 2 TPS (1 junkyard and 1 new one) and switching those out didn't resolve the issue. Let me know if any other OBDII readings may be useful to help diagnose the issue.

Re: Swap Startup: Stumbling
 

There should be several PID's for the Throttle Position sensor, so any OBDII reader and software should be able to identify them. I am most familiar with Torque/Torque Pro but I believe thats Android only.

Once you can find the TPS gauges it should illuminate some. I didnt see mentioned; are you drive by wire or drive by cable?

Re: Swap Startup: Stumbling
 

Cable, the only one I can find is "Absolute Throttle Position" but it only tells you how far open the TPS is which isn't very useful.

Re: Swap Startup: Stumbling
 

So, that actually is useful. What are your readings at idle and with the pedal floored?

With DBC at idle your TPS should show "0%" since you have an IAC to keep airflow correct. With DBW's the TPS won't or shouldn't show 0% at idle because it does NOT have an IAC and the TPS+throttle actuation motor is what keeps the blades open the appropriate amount. If, for some reason, your TPS is showing > 0% at idle then off idle stumble would be expected because it would push more fuel than is needed.

Does that app have calculated AFR or Commanded AFR? With narrowband O2 sensors the most accurate you will get is "rich" or "lean" - the actual numbers don't matter but it might help illuminate some of the problem.


I also noticed that you're running a manual trans. Did BP flash it with a non-electronic trans tune? Occasionally that can cause weirdness, especially on deceleration . Your issue sounds different, but its a thought.

Re: Swap Startup: Stumbling
 

They were supposed to tune it as a manual but honestly they are not doing a very good job of making me feel comfortable about the tune as they didn't even turn the fans on. The TPS checked out ok 0% at idle and 100% at WOT.

It has 02 lambda which always reads 0, 02 voltage which doesn't tell you much, fuel % trim which was 0.8% on bank 1 and 1.6% on bank 2 (no idea what that means), and calculated load value of 2.0% (no idea what that means). I want a AFR reading like 10:1, 12:1 etc but don't see that. I hope that 0.8% is not the real AFR reading.

Re: Swap Startup: Stumbling
 

I am having a tuner come over next Thursday and see what's up, I can't really tell anything from this app thing I have as it seems to say yup sender is working rather than giving any real data like fuel maps.

Re: Swap Startup: Stumbling
 

Yeah, the only ones that will actually pull a tune and show those tables for these GM ECu's are ones like HPTuners with their adapter (there are a few others, just an example) and that would be approx $400 - not worth it unless you want to be able to apply/modify tunes yourself. You could get just the hardware for logging purposes but thats $300 of the $400 to tune it yourself.



Fuel trims of < 5% are normal so don't worry about that - thats just how much the fuel is being auto adjusted to keep it near stoich. The only way you can get an AFR reading like that that's accurate is with a wideband O2 sensor - narrow bands are only accurate at 14.7 (stoich) - other than that, they pretty much only say "RICH" or "LEAN." Depending on the car, and the software you use, you can occasionally get a commanded AFR and a calculated AFR but the only accurate way to get what the AFR actually is, is with a wideband O2 sensor. Factory ones are narrow band.


Let us know what the tuner says - I am invested now!

Re: Swap Startup: Stumbling
 

Well that didn't go as planned. I got a base tune by BP Automotive who forgot to turn the fans on and their Customer Service sucks so I have 0 faith in that.

I had a tuner come over today and he messed with the truck for about an hour. He says the TPS is reading correctly but the ECU cuts out after about 30 seconds and he can't get a reading on HPTuners after that. He says that it could be a bad ECU (wouldn't BP Automotive know this when they loaded the base tune?), an issue within the BP Automotive harness, or a mechanical issue which he doubts as it runs good with the TPS unhooked. He did this at no cost.

He says he will bring a known good computer and test everything for $100 assuming his ECU works. He also said for a tune he needs to buy credits which are $200 (I know they are but I assumed he would have an unlimited pass and not charge the full $200). Then of course the tuning fee once the issue is resolved. Now, there are tuning shops around but I don't know how much this would cost there but he said it could be a rabbithole of expense depending on what is wrong. Advice please? Is the recommendations or cost out of line?

Re: Swap Startup: Stumbling
 

The costs sound reasonable - honestly, even though its a hard pill to swallow, its probably your best bet to write off the BP Automotive tune and let the local tuner work his magic.