[JohnWR]

I have a 2007 Sky Base. A few weeks ago, when I got in it it wouldn't turn over, just clicking. After trying several times, and holding the key in it started, then immediately stalled out. Doing this a few more times, it eventually started to run, but it would lose power every 3-5 seconds, rpms would drop to almost zero and then go back up again. When this was happening, I noticed i could hear chattering from the fuel pump relay. I swapped the relay, no change, same issue. So now I thought maybe I had an electrical issue. Reading around on the forums, i thought maybe i had a bad ground connection at the engine block. I disconnected the battery, disconnected the ground at the block and cleaned everything up really good, including the battery terminals and connectors. After reconnecting, it started to run normally. Problem solved (or so i thought). I had driven it several times after that and all was good, until today. I took it for a ride, just about 4 miles down the road, and on my way back home it started acting up again. It was dropping rpms then going back, dropping again, over and over. After i got home, I thought maybe i had a problem with the actual ground cable, i disconnected the battery again, checked everything out and it doesn't seem to be corroded. Now when i reconnected the battery, it started running normally again. Checking the voltage under load, when it's running normally is showing 12.8 volts from positive to ground on both the battery ground and the engine block ground. I'm now at a loss as to what the issue could be? Could this be a bad battery causing the immobilizer to get messed up? If that's the case, once it's running, shouldn't it just run normally? I.e. why would it cut off and back on again, since the alternator should be supplying enough current?

There are no pending or permanent codes stored. The check engine light does blink when it starts to run rough, but still no codes. Any assistance would be greatly appreciated.

I'm going to say that 12.8 V is too low while running. You should be seeing 14 V +. How old is the battery, and what is the voltage when not running?

I suspect a bad battery or a bad generator.

 

[JohnWR]

Yea, it was only at 11.5V when not running, so I was thinking the battery might need to be replaced. But also thought me starting it and shutting it off over and over might be why the voltage is low. But the behavior seems odd, i.e. disconnecting the battery then reconnecting it allows it to run normally for a while and then it started acting up again while driving, even at high rpms? Though i guess it could be the alternator, and that could be the cause. Do you know how many volts the alternator should put out?

14.4V is nominal while charging, and 11.5V is generally considered to be a "dead" battery.

A bad battery will drag the running voltage down, and continuous use under that condition will burn out the generator.

I would change the battery first, then see what happens. A bad battery will cause some really strange behavior.

 

[JohnWR]

I haven't been driving very often, which is why i originally suspected the battery. But after i disconnected everything, reconnected it, it seemed to run without issues for several short trips. No hiccups at all. I didn't test the voltage of the battery earlier, because my multimeter's battery was dead 🙄. That, and once it started acting normally - my past experience as a 35 year "back yard mechanic" told me the battery was probably fine. However, the computers in these cars sometimes have other ideas. I don't think it's the fuel pump, because when it won't even crank, nothing in the ignition system seems to work and when it's running i can hear/feel the fule pump relay activating and deactivating coinciding with the loss of power/rpms. I will change the battery this afternoon and hope that fixes it. I don't like how unpredictable it is... taking it for a test drive could leave me stranded.

When you run it after changing the battery check the voltages. If you are not getting in the range of 14V you still have a problem, likely with the generator.

 

[JohnWR]

The fusible link failure results in the same voltage running or not, so it probably isn't that.

I would see how the battery tests, and see what the running voltage is with the new battery. Regardless of anything else you should be over 14V running.

 

[JohnWR]

I'm going to say that your generator is okay. With the fuel gauge dropping like that it sounds like a loose wire, fuse, or relay.

 

[JohnWR]

I just wanted to check in and provide a quick update. If you've read all my posts here, you know I changed the ignition switch about 2 weeks ago and immediately had a "no crank" which required me to disconnect/reconnect the battery. Therefore, I assumed the issue was not resolved. However, ever since that time, the issue has not happened again. It has been cranking and starting every time i ask it to. I've driven it on multiple small drives and have started it at least once a day since that time and let it run for a few minutes. I'm cautiously optimistic that the ignition switch was the cause of my problems, but if I have an issue again, I will update this thread. I want to thank everyone who took the time to read my post and offer me suggestions, it was and is truly appreciated.

I hope that you found the problem.

 

[JohnWR]

So today i drove the Sky about 60 miles - 2 separate 30 mile round trips. It ran fine for the first 45 of those miles, but it started acting up on the way home on the 2nd trip. Because i had about 10 miles to go, I decided to run it like it was for a while and see if i noticed any other symptoms/gauges doing anything odd. During that test cycle, the CEL was flashing and the engine was cutting out intermittently. It would run normally for a stretch and then start acting up again. What I noticed was the only thing other than the RPMs dropping/engine cutting out, was the fuel gauge was actually goin up when the engine was cutting out, all the way to full at one point. During the last 3 or 4 miles of the trip the engine started running normally again, and the fuel gauge settled back to what i think was the normal position. The other information seemed to be fine, the speedometer wasn't jumping, the engine temp looked to stay steady, no other flashing lights or odd behavior.

Does this give anyone any ideas?

I think that @agent008 could be on the right track, but the problem could actually be anywhere from the fuel tank to the ECM.

That said, with the CEL flashing there should be a code stored, even if the light is no longer on. Assuming that you still are not seeing pending, live, or historic codes, the only thing I can think of is a problem with the ECM.

 

[JohnWR]

No codes, but I did another test, disconnected the MAF and I got 2 codes, disconnected the camshaft position sensor and got another code. I'm not saying it isn't the ECM, but it does seem to be capable of storing codes. I started the process of removing the trunk liner - this doesn't seem like a very straight forward job. Any tips? Also I have an endoscope and used that to inspect the wiring and connectors on the sending unit, it LOOKS ok, but of course I cannot be sure without getting my hands on it.

It is the fact that you have been able to force codes, but don't get one when the car is running its worst, that makes me suspect the ECM.

The liner mostly lifts out, although you have to fold it in some to do that. It has been at least a decade since I had mine out, but once the top drain tubes are out of the way and the light is snapped out of its hole it was mostly a matter of contortion. I do not remember anyhting "hidden". Obviously you want to be careful that it doesn't spring open at the wrong time and damage paint.

 

[JohnWR]

When I saw the mouse nest, I was actually happy - figuring I found the issue. However, even though there was a lot of debris on top of the tank, the wires looked to be untouched - no chewing anywhere between where the wire is not running through the interior of the car and the sending unit and my very (un)scientific test of wiggling the wires around in that area didn't seem to affect the car at all - How can I actually test that wiring and the sending unit?

@agent008 is part of the way there, but you also have to test the wires for short to ground, short to +12V and short to other wires. I have usually been able to visually inspect the wiring, looking for damage to it or to connectors.

Also, any advice on how to "test" the coils? I can pull the plugs easily enough and check them, though that would really be a head scratcher to have a bad plug and/or coil causing me a complete loss of power to the ignition system? Honestly, even a short on the fuel pump sending unit causing a loss of power on the ignition side would seem odd to me.

Normally, as @sahein stated, a bad coil will result in a misfire code, and that code is usually specific to a cylinder. Finding the bad component (coil, plug, injector, etc) generally involves switching components between cylinders and hoping the misfire switches to one of those cylinders. You don't have a misfire code, so that technique is not available to you.

Does anyone have a pinout diagram for the PCM connectors for a 2007 sky base?

Yes, I can post the ECM pinout tonight.

 

[JohnWR]

agent008,
Thanks for taking the time to post those, but do to my own inexperience I'm not sure how to read the diagrams? Do you know how I translate what's in the schematic to the actual ECM/PCM connector and Pin? I.e. if I wanted to trace the Camshaft position sensor - Exhaust, how do I know which connector to look at on the ECM and which pin? Also, do you have the schematics for the rest of the components in the ignition system?

This may help.

 

[JohnWR]

....... Note that I was able to communicate with the ECM, and then I wasn't - does this communication go through the BCM first?
.......

The high-speed LAN is a two-wire daisy-chain network, and an interruption in any part of it will disable the car.

Physically, the wiring goes:

1. DLC (Data Link Connector)
2. Data Link Resistor
3. BCM (Body Control Module)
4. VCIM (Vehicle Communication Interface Module) (OnStar, if fitted)
5. EBCM (Electronic Brake Control Module)
6. TCM (Transmission Control Module) (If automatic transmission is fitted)
7. ECM (Engine Control Module)