three83

iTrader: (1)

Started having problems with my truck back in May. Well we finally fixed some of the problems and have a good idea what is causing the rest of the problems. Problems, Troubleshooting, Solution below.

Problems:
1. Hesitation at WOT launch from idle
2. Hesitation when going WOT rolling 20mph or slower
3. slow to downshift back to 1st when driving 35mph or slower (4 - 6 seconds after gas pedal is on floor board)
4. poor fuel mileage
5. random rough idle
6. stalled 3 or 4 times when coming to a stop (over the last 5 months)
7. Misfires on 6 of the 8 cylinders with 7 and 8 having the most.
8. voltage varies between 12.5 and 14.6.
9. Long Term Fuel Trims went from staying around 0 to +6.

Codes:
Got these codes on Monday, first codes since problem started in May.
1. 1301 - Class 2 Communication Circuit Low Voltage
2. P1626 – Anti-Theft System Fuel enable Circuit
3. P0300 – Random Misfire

Troubleshooting:
1. removed/sold predator programmer
2. scanned/tuned with HP Tuners
3. Changed Plugs - NGK TR5 (NGK recommended .040 gap)
4. Changed Wires
5. Cleaned Throttle Body
6. Checked for vacuum leaks using vacuum gauge (between 20 and 21 in Hg)
7. checked fuel pressure (62psi key on engine off, 60psi idle)
8. Cleaned MAF
9. Swapped coils on Cylinders 7 and 8 with cylinders 5 and 6. No change when coils were moved.
10 Swapped injectors on Cylinders 7 and 8 with cylinders 5 and 6. Misfires followed injectors.
11. Checked/Cleaned fuel rails and injectors
11. tried MAP Sensor from a friends truck
12. had battery and alternator tested
13. checked catalytic converter

Solution for hesitation/downshift problems:
Today a friend of mine took the MAF off of my truck and replaced it with the MAF from his truck (same year/make/model). Went drive my truck and the WOT Hesitation and Downshift issues are gone!!! Going WOT rolling about 10-15mph, it instantly starts spinning thru 1st gear and chirps 2nd.

I think my MAF isn't reporting the correct amount of air coming into the motor but still reporting within normal operating range which is why it there were no codes generated. If the MAF wasn't showing correct air coming into the motor, the air wasn't met with the correct amount of fuel causing a lean misfire.

Problem Remains
Still have the rough idle.....It will idle smooth for a while, then go to idling so rough the whole truck shakes, then will clear up and idle smooth for a while then start the rough idle again. I'm thinking fuel injectors need to be serviced or replaced.

I talked to a friend that is a mechanic at a local dealership to ask about the codes and issues with my truck. First thing out of his mouth before I could tell him everything was "dirty or bad MAF, Throttle Body, and/or Fuel Injectors would be the most common causes."

He said the random misfire code is common but the other two are rare and most likely "False Positive". If they return after being cleared it could be due to the PCM and BCM losing communication. The Anti-Theft System is part of the BCM and when communication is lost between the PCM and BCM it could cause the fuel to be shut off causing random misfires. He said these were most likely "false positive" codes and not the cause of the problems with my truck.

Now I just need to catch up with all the medical bills from knee surgery and being out of work for a month so I can fix my truck.

I hope this helps, it has been a PITA trying to figure out the cause of these problems that happen at random and don't generate a code.

Anyone have issues with the BCM on a 05 Silverado CrewCab?

budhayes3

iTrader: (19)

I wonder if the 1301 - Class 2 Communication Circuit Low Voltage and P1626 – Anti-Theft System Fuel enable Circuit have anything to do with the Predator programmer being in there??

three83

iTrader: (1)

I don't think so because the predator tune was installed in April '05 and removed in May '09. HPT was installed in May '09. These codes didn't show up until a little over a week ago.

The MAF was causing most of my problems. Today I had to drive 130 miles for work, so I checked fuel mileage....19.6mpg. Before I swapped the MAF I was getting between 15 - 16 mpg on highway and as low as 10mpg in the city.

I still have a rough idle and the LTFTs are +9, they were at 0 before I started having these problems. I'm going to buy a new MAF from the dealership and going to bring my stock injectors to a local injector service shop. Once I have a new MAF and know the injectors are spraying good, I'm thinking all will be back to normal.

Just curious as to why my MAF was making my truck run like **** but no codes pointing to a bad MAF. This started after my truck went to a shop for an alignment. A friend thinks the shop swapped my MAF with a bad one then cleared the code. Little bit of a stretch but I guess it could happen.

streetdraggr007

eh I doubt a shop would do something outrageous like that