C5 Jeep

From time to time my 04 C5 cranks but won't start. Here is what I have observed.
1. I hear the fuel pump run when the key is turned on.
2. It usually but not always starts when it is cold.
3. It can take up to 15 minutes to start when it is hot but sometimes it starts right up when it's hot.
4. It seems to be getting worse.
5. The only code that might apply is B2723H - Pass key detection circuit. After writing down all the codes I reset them and even after it didn't start, that code did not reappear.
6. I cleaned the VATS pellet, no change. I don't have a spare key but one is on order.
7. The battery voltage measured on the fuse block reads 13.3 without the ignition switch on, 12 with it on, and 8.3 when cranking. My battery is behind the rear end and I have a 2 gauge cable running to the starter.
8. I've had this car for 6 months and it started fine for the first 4 months.
9. I first noticed the problem when I released the key from the start position before it fired up. Then it would take 10 attempts or so to get it started.
Any thoughts?

Bill Curlee

WOW! 8 volts is WAY to low for the PCM and BCM to function properly! I would start there. Each module has a LOW VOLTAGE CUT OFF and that is right at the cut off for the BCM / PCM. You probably have low voltage codes for the LDCM & RDCM also.

Have you ever seen NO COMMS messages?


Have your battery FULLY tested! Check for Cold Cranking Amps (CCA and Reserve capacity and when the battery is fully LOADED, see what the minimum voltage is.

Next: Check for clean and TIGHT connections at EVERY battery connection/connector. If the connections at the battery and any of the connections are not 100% clean and tight, that will present a large voltage drop at that connection.

Battery Ground: How did you ground the battery NEGATIVE terminal and connect that to the engine block? If you used the FRAME at the rear to connect the battery, that could cause a high resistance connection.

Hope this helps solve the issue.

Bill

C5 Jeep

Thanks Bill.
Regarding "No Com" messages, I've always had two no com messages, A0-LDCM - no com and A1-RDCM - no com and I've never known what they meant.
Per your advise, I removed the battery and did a load test with an old Sears resistance type load tester and it passed the 10 second test. I don't have a way to test cold cranking amps and reserve capacity but I can go somewhere and get that done if it still seems appropriate.
The battery is 6 months old with a cold cranking rating of 1000 amps @32 degrees F.
I fully charged the battery and the cranking drop is now to 9 volts.
Regarding the battery ground, it goes to both the transmission and the frame with the bigger wire to the tranny.
I checked all of the connections and they are all tight with no signs of corrosion.
I'm suspecting the length and gauge of the positive lead might be an issue. I checked my paperwork and the positive lead is actually 4 gauge, not 2 as I thought and it is 15 feet long. I ran an online voltage drop calculator figuring a starting voltage of 11 and it came up with 9.2 volts at the engine using 250 amps as the starter draw.
One more test I'll do on Monday (going away tomorrow for the weekend) is to measure the voltage drop while cranking at the battery.
One option that comes to mind is to run a separate power wire from the battery to the computers. Thoughts?
Thanks again for your help Bill.
Bob

Bill Curlee

Bob

BANG,, It just hit me!!! , I think I may have an answer to your issue. Grounding the battery to the transmission, Is a poor path to the engine. You need to get a good direct GROUND path to the engine block.

Do you have a ground wire from the relocated battery to chassis ground??

Measure the engine compartment FUSE BLOCK B+ terminal to chassis ground in the following conditions:

Cold Iron, engine OFF

Ignition switch ON

Cold Cranking the engine

Measure the Passengers Foot Well Fuse block B+ terminal in the came conditions.

What does your IPC Volt Meters indicate with the ignition ON and when the engine running?

What is actual battery terminal charging voltage when the engine is running?

Bill

4DRUSH

When the battery was relocated, did they just connect everything together in the old battery compartment & run it back with 4 gauge?

C5 Jeep

Thanks again Bill. As I said, I'm heading out in the morning for the weekend and will run the tests as you suggested on Monday
Bob

73Corvette

C5 Jeep

Thanks for jumping in 4DRUSH. When I put the Jeepster body on the C5 chassis, the place where the battery should go disappeared so I relocated the battery in the back. The hot lead goes directly to the B+ terminal on the fuse block under the hood with a second cable going from there to the starter. The negative side of the battery goes to both the frame and the transmission at the back of the car.

Bill Curlee

C5 / JEEP

My Son installed a LS2 in a 97 Wrangler when he was in the Army.

Atlas Xfer case, some bad AZZ front and rear axles, Long Arm suspension and a bunch of other stuff..

It pops wheelies and does a pretty quick 1/4 mile for a JEEP!!! LOL!

You know what JEEP stands for??,,, Right?

JUST EMPTY EVERY POCKET!

Bill

73Corvette

4DRUSH

I'd also try 2 gauge welding cable from battery to terminal on front of Jeep

Bill Curlee

LOL

I knew that was coming!!

So,, here's is a You Tube Vid for ya..



Here are some picts:

73Corvette

DDDDamn....what a great way to recycle an LS1

C5 Jeep

I ordered some 2 gauge cable, enough for the pos and neg from the battery to the engine compartment which should raise the cranking volts up almost one volt at 250 amp starter draw. It is due to arrive toward the end of the week.

Do these numbers tell you anything you didn't suspect before?

Thanks again.

Bob

C5 Jeep

What a great looking LS1 project.The video looks like the first start, always an exciting moment.

My Jeepster is at the other end of the spectrum. It's ride height is a couple of feet lower than your son's. It is basically a re-bodied C5 with the same ride height as a C5. It sits on a C5 chassis, has the C5 interior, etc. I'll send some images from my other computer later today.

Bob

Bill Curlee

Bob

What HP level is it at and do you surprise many people???

All I can tell you is,, having the main current path flow through that much aluminum and 4-5 bolted joints, is NOT the proper high current return path for a large current circuit.
Plus, the electrolis that it can cause in your drive train IS NOT predictable or desireable.

Bill

C5 Jeep

The engine a stock LS1 that's been tuned so it's somewhere between 350 and 400 HP and yes it does surprise folks.

I think the best way to see some images is on my website, www.bobpelikan.com where I've posted images of the build as well as some of the finished car.

I drove it some today and it started fine all day. I noticed that the charging voltage had dropped to 13.9 and 14 volts later in the day regardless of RPM from the 14.3 I reported earlier.

Thanks again for your help.

Bob

C5 Jeep

Hi again Bill,
Believe it or not my intermittent no start issue continues. Here's some history since we last communicated.
1. Per your suggestion, I ran a 2/0 cable from the battery in the rear to the engine block post next to the starter. No improvement.
2. I discovered that if I left the key on for 15 seconds or so after a no start episode it almost always started right up.
3. This worked for two months but last week I got stranded for 45 minutes when none of the tricks worked. It finally started just before the tow truck arrived.
4. When I got home I put a volt meter on the red wire (Ignition +12V) going to one of the coils and it is shows no voltage when the car is doing it's no start thing.
5. I left the key on for a few minutes while I was doing this test, heard a click, and bingo I had 12V at the coil and it started.
6. I swapped out the Ignition relay with one of the fan relays and it started 10 times in a row so I patted myself on the back and gave myself a gold star for being such an incredible trouble-shooter. I thought this was the problem for sure because when I first got the car running the Ignition relay had lost it's ground and it chattered a ton while chased down the issue. I figured the contacts were damaged.
7. The next day I loaded my wife into the jeep and headed down the road for a drive down the coast. Less than a mile down the road the stability control warning light came on, it went into limp and died. I cycled the battery disconnect to reset the PCM and it started after several tries only to die again at the next light. I swapped the Ignition relay for another of the fan relays and it started and acted normal. I drove it home, and then around town and up and down the highway for 45 minutes to see if it would quit again. It ran fine and restarted every time.
8. I suppose there is a chance that the second fan relay was defective but the fans have been operating normally all along so I wonder. And what if anything is the connection between the no starting and the Stability control/limp mode thing?
9. The only codes on the DIC have to do with lights, airbags, AC, and the remote control FOB.

Any ideas. I'm at the end of my rope.

Thanks.
Bob

Bill Curlee

I read a few sentances in to your reply and my immediate thought was you have an ignition switch issue OR an issue with an ignition powered relay.

Give that a check...

C5 Jeep

Thanks for the reply Bill. I'd come to the same conclusion on the starting issue but would the Ignition switch/Ignition relay also cause the stability light/limp mode issue, number 7 above?