Need help tracking intermittent problem with 6.0

[sadam_husain]

So, my original question still stands. What can I plug into the ODB ii that will record the ECM so that when it happens again, in addition to seeing if there's a code, I can check what, if anything, happened in the engine parameters. Do I need an HP Live box?

Theres plenty of free datalogging software available off the net you can load onto your laptop and connect to the OBDII port to monitor what's going on with your engine that will let you go back to view and pinpoint exactually what was going on when the engine exhibited problems

 

[workingdog]

So, been able to drive it some more. The behavior does not throw a code. I guess that eliminates all the possibilities that would throw a code. What could make the engine have a sudden loss of power that lasts less than a second? Loss of power or ground to the computer? To the coils? Fuel shut off by the computer because of bad TPS reading (this is DBC, but there has to be a sensor on the throttle body)?

 

[SuperBuickGuy]

delay in the code - DBW and cable style both take the pedal input under advisement, it's possible that the delay that GM puts in there to protect parts is still somewhere rattling around the code. If you had HP tuners, you could go look at whether there's a delay there or not... or ask your tuner if he changed it (he needs to answer "yes" to that question).

 

[workingdog]

I'm not following. If there was a delay, wouldn't that happen all the time, instead of at random times like this is?

 

[SuperBuickGuy]

it depends on the throttle position and/or how rapidly you press the throttle. so if you're already touching the throttle, you get instant response, if not or you're on and off a delay can happen. It is absolutely the most frustrating thing - especially when you're wheeling. I think GM did it to protect the transmission, and I'd like to ask the engineer why - preferably somewhere where his cries for help will be unheeded. The only forgivable thing is, though, it can be programmed out.

With that said, I'm not there - so you're only getting "stuff that's either happened to me or I know of through direct experience" .... at this point, outside of that my next suggestion will be a data logger and after that an oscilloscope (thank you spell checker)... way too often when diagnosing problems we get to the deep end of the pool and find out it was something simple.... a broken wire, cracked plug, etc... in short, good luck

 

[workingdog]

No, that's not it. I'm getting instant throttle response. I can be driving along, steady throttle, flat road, and it will just drop out like the fuel or spark has cut off for a tenth of a second, and then it's fine.

 

[RAYJON]

I am wondering how they got it to work right without a speed sensor?? you can hook it up to EFI live and see how its programed. EFI live can data log it and see what it's doing, There is alot of varying tables in the gm computer and speed is a major one for fuel and spark. The delay super buick was talking about is throttle response and WOT both should be 0, gm has a 60 sec delay on WOT in most applications..

another question what kind of fuel system is in this thing??? if they ran some cheep frame mounted pump with undersized wiring or small tubing it may be overheating and you are loosing fuel pressure. this would explain the low performance and no codes... you need about 55psi at the rail consistantly, fj40 fuel lines are not going to cut it on a 6.0, 3/8 minimum from the pickup to the regulator with no restrictions(crap in the lines causes some real weird s*** to happen due to varying pressure).. and at least a #10 wire to power the pump. If the pressure is good check the voltage at the pump with it running, undersized wire will drop the voltage alot. it needs 13 volts constant for the pump to work well.. also is this a return less system?? return less systems have to use the gm in tank pump and proper wiring to work.. there are ways around it but most just swap to a return style system..


simple stuff first fuel, spark and compression..

 

[workingdog]

Everyone else has started with fuel. I'm on my third pump, this is an $800 pump. It has all new lines, flow from tank to engine was verified. I now have a fuel pressure gauge in the cab and it's holding 50 to 55 pounds all the time, it does not drop when this behavior happens. Also, if it was fuel pressure, I think (I don't know) that it would feel different - more like a stumble with a beginning and end. The way this things goes weird and then comes back is so abrupt is unique.

 

[Mace]

Electrical would be my guess. Do you have a tachometer in it?

 

[workingdog]

Yes, I have a tach off and I use ScanGauge off the ODB ii port.

I agree it feels electrical, but I don't know if I should be focusing on the computer turning the engine off for a second, or some other thing that temporarily disables the engine, just for a fraction of a second.

 

[Mace]

at this point, you just have to work through everything one piece at a time. Does the Tach flutter when it drops power?
If it's a spark issue you may see the tach cut out. If it's fuel, the tach will still spin with the motor..
(obviously there will be some change due to the motor cutting out)

Diagnosing this is likely just going to be a matter of working through everything. Painful..

 

[workingdog]

I agree exactly, so where do I start? Since I'm going to have to diagnose this as I'm driving around town (it won't do it on demand, what can I install in the cab (other than fuel pressure) that will me. I'll keep the RPM up on the gauges and see if it moves. Is there a way to determine if it is the computer making a decision to shut the motor down? Whether to chase the ECM or not seems to be the first decision I have to make.

 

[Mace]

Anytime the computer shuts the engine down it should log an error..

laptop and data logging as was recommended before is a good start.. F'n sucks, but it is what it is with computer controlled engines.

Likely it's either the ECM or the wiring (not much else left) so knocking one out first will matter.

 

[workingdog]

Just order HP Tuner package. Hopefully it will show me something (once it gets here and I figure it out).

 

[Mace]

You have my sympathies.

 

[workingdog]

So ... I put an Android phone and an OBD ii Link MX wireless adapter in the truck (We've had bad luck with the wireless version of these that connect to iOS devices like iPhones. They can't keep a connection. But the Android version uses Bluetooth and it's much more stable.) and one of the oxygen sensors is right at .44, .45, .46 - but the other one is all over the place, almost random between 0 and .9. Could be a bad connection, could be a bad sensor. As I am pondering that, the truck cuts out like it does and the oxygen sensor is reading zero. Every time it does that power loss, the sensor was at 0. I'm sure the ECM is freaking out getting that reading. So I'm going to figure out how to test one and then under the truck to pull the sensor and see what's wrong.

 

[spotcruiser]

I don't know why you're seeing 0 volts on the one O2 sensor, so you might have a connection issue. Seems like it would throw a code, though. The other O2 sensor doesn't seem correct, either. Both sensors (forward sensors, not after-cat sensors) should constantly cycle above and below 0.5 volts (between 0.1 volt and 0.9 volt). Above 0.5 volts is rich; below 0.5 volts is lean. The cycling above and below shows that the ECM is constantly tweaking the fuel injection to maintain the optimum A/F mix.

So ... I put an Android phone and an OBD ii Link MX wireless adapter in the truck (We've had bad luck with the wireless version of these that connect to iOS devices like iPhones. They can't keep a connection. But the Android version uses Bluetooth and it's much more stable.) and one of the oxygen sensors is right at .44, .45, .46 - but the other one is all over the place, almost random between 0 and .9. Could be a bad connection, could be a bad sensor. As I am pondering that, the truck cuts out like it does and the oxygen sensor is reading zero. Every time it does that power loss, the sensor was at 0. I'm sure the ECM is freaking out getting that reading. So I'm going to figure out how to test one and then under the truck to pull the sensor and see what's wrong.

 

[workingdog]

Yes, the other sensor is acting like an after CAT sensor, which it's not.

 

[workingdog]

So, I looked closer at the ODB ii gauage and it was set up to read bank 1 sensors 1 and 2 (which explains the .45 reading) - so I reconfigured to read bank 1, sensor 1 and bank 2 sensor 1 and will go out and see if I'm getting 0 on both sensors at the same time.

 

[sadam_husain]

I don't know if I'd be too convinced your problem lies with o2 sensors they only shift the ECM between open and closed loop mode and trim the fuel they don't have enough control to make the system run as if its in limp mode. I did once have a problem like your having but I don't think its what is occurring with your truck but I had a problem with my fuel tank not venting properly (a carb tank being used for efi) and on longer trips the tank would create too much vacuum and the external fuel pump would cavitate and not generate enough pressure at the rail and the engine would eventually die until you released the fuel cap to remove the vacuum in the tank, I've always run a fuel pressure gauge on the rail since then.