Hey Bill (or anyone else)

Do you have anything showing the splice pack locations? Specifically looking for the common link between the MAF and the TAC module. Having some funky issues with the car ('98 coupe) shutting off while driving and throwing a MAF code, even though the MAF is new. OBD data shows a spike in the MAF signal when this happens and it's also showing a spike in the throttle position data. The only link between these two that I know of is the ground side. Cleaning the lot of them will be on the list, but finding these specific points is first up.

Thanks!
Dave

 

What MAF DTC are you seeing ???....the MAF, TAC Module, and PCM share a common ground which is above the starter (G106). What is exactly "spiking"... MAF and TPS voltage ?????

 

P0101

The reported airflow will suddenly jump to 4-5x the actual value. Not sure what full scale is, but it must be close. At the same time, the indicated throttle position spiked to near 100% as well. Then the car dies.

MAF is brand new since the issue started, throttle body and TAC were swapped with my '01. Not much wiring in common between the MAF and TAC.

 

With the P0101 I'd look at the MAF voltage unplugged...12 volts on the PINK, 5 volts on the YELLOW (signal) and the black/white is ground...I'd also look at the MAP sensor and with KOEO you should see around 14.9 at sea level. You can check both TPS signal voltages ( dark blue and pink wires) with KOEO at idle and WOT...report the 4 voltages you are seeing !!

 

Been travelling, so not much time to fiddle around with this thing.
Driving at 55mph, MAF (via scanner on the ALDL) is 25-30 g/cm3. Throttle position ~17%, Engine load ~17%, Timing advance ~41deg. Manifold Pressure=3.2psi. Everything looks fine.

Then...
MAF jumps to about 98g/cm3, Throttle Position then jumps to 65, then 86%. MAP also jumps to 6.6psi. Engine load jumps to 58%.
As this happens, the engine sputters and dies.
The high values all last for about 6 seconds (which was probably the amount of time it took to reset the code, at which time the engine refired).
Data rates suck, so it's impossible to tell for certain which signal is leading/trailing the others, if at all.

So there are 2 coincidental spikes (MAF & ThrottlePos) which are completely disconnected to each other except through the grounds. Thus the search for the splice packs and ground location. G106 is the battery negative terminal, so there has to be a splice somewhere nearby.

 

Unplug the MAF and see if the problem persist.. What year C5 do you have??

 

It's a '98

Haven't unplugged the MAF, but unplugging the IAT will make it run better, but it will occasionally "cough". Just enough of a stumble to jerk the car before it recovers. On occasion, it'll be severe enough and long enough to lose considerable speed. Need to dig up the data in that condition....

 

Get or obtain a scanner that can read LIVE SENSOR DATA. See what each sensor reads with the KEY ON ENGINE OFF (KOEO) and see what they read with the engine running. Example- That IAT Sensor should read ambient air temp at KOEO and should read close to outside ambient when air is flowing through the intake ducting. The temp reading will rise some due to engine /under hood temps but it should be close to outside temp. Same with the coolant temp sensor. Should be outside /under hood temp at KOEO cold engine and rise as engine heats up.to normal operating temp.

Bill

 

I can read live, it's just a slow update rate. No issues with either the IAT or ECT. IAT goes to -40 when unplugged, as it should.

 

C heck the O2 sensor heater voltage and current.. Make sure its in spec.

BC

 

I certainly can do so. I'm not seeing an obvious link. What are you thinking?

*edit* ran both cars at idle from a cold start. Roughly 50 degrees outside.
On the '98, the sensor cycles between ~150mV to ~800mV.
My '01 does nearly the same, except the low-side is just under 100mV.

 

Should the car be able to idle with the MAF disconnected? It won't. Separate IAT and MAF on the '98, so it's only the MAF being disconnected.

 

I recently purchased a 1998 C5 and it has a long list of error codes that are intermittent. I thought I would have to live with them or spend mega bucks to have modules replaced... This sounds like the place to start!!

 

Buy a brand new battery first! Make sure you charge the battery before you put it in the car, it should have at least 13 volts. That alone will get rid of many problems. Corvettes hate weak batteries! Then do the grounds, easiest ones to start with and that cause many problems are the ones on the frame inside the engine compartment one is below the windshield washer tank, the other ison the other side below the radiator tank. Make sure all corrosion and paint is gone!
Then if you still have gremlins do all the grounds!
Good luck!

 

Thanks for the info! Appreciated!

 

100% DIT DOT CORRECT!! Let us know how the battery checks out.

Bill

 

My 2002 Corvette has been acting up last Saturday after cleaning all thee grounds I lost the radio,fuel gauge,temp gauge and it said low engine power when I got home I check the codes and the BCM had code u1064 lost connection with PCM also had same code at LHDM and RHDM could this be the BCM any help would be appreciated. I hope this is the right place to ask this question???????

 

With what you're seeing plus the U codes (no comms) I'd be thinking you have issues with your serial data bus...is the car a "no start" or "start and stall" ???...were you seeing the fuel gauge go to "E" and the water temp gauge max out and also many DIC messages...i.e. low fuel, reduced engine power, service vehicle soon ????...what's happening is one of cars various modules is losing a power or ground and 12 volts or ground is getting on the data bus where it shouldn't be. if the car is not starting find the 2 splice packs or "Star Connectors" that are located to the left of the BCM (pictured with BCM/PCM jumpered and combs removed)...remove the bus bar or "comb" on the one with the fewer wires that is located on top of the splice pack...squeeze the ends and it should pop off...now see if the car starts...if not you can pop off the other one but you have to take a jumper wire and connect the light green (BCM) to the dark green (PCM)...if the issue is NOT on either the BCM or PCM the car will start...if the car doesn't start it may be on one of those 2 modules...also when you pop off the comb take some emery cloth and clean them until the metal is shiny bright !!...you can start there...a lot of times the driver door module has some wiring issues...when you open the door inside the rubber "accordion" boot is a connection that becomes loose or corroded...you can look there to since the door is opened and closed many times !!...YouTube video enclosed too !!
PS...as in the video you can use a voltmeter to see if you have 12 volts or ground on the data line wires !!...a scope is needed to see the 0-7 volt square wave on a good wire but with a voltmeter you will see less than 1 volt dancing around !!

 

If you want to "edumacate" yourself on the "CAN bus" here are 2 great videos !!...grab yourself a six pack and enjoy !!

 

Thanks for the places to look just to let you know that the car starts and when this happens I disconnect the battery for about a hour and the car is where it was before this happens I drove 200 miles and no problem the next time I drove it home when it happen again about 100 miles and ran ok just no gauges and was saying low fuel reduce eng. power check gauges light was onI have come to the conclusion that the BCM is bad with a intermite problem between the PCM and BCM I am going to change the BCM next week and I will let you know it works out. Thanks for the information I appreciated very much.