: 4 cylinder Northstar - 97 DeVille



longisland516
05-30-05, 05:47 PM
This weekend I was driving my 97 DeVille with 125k miles from NY to Atlanta. Close to SC the check engine light came on and the car started to loose power. The code set was P0151 Front O2 Sensor, Bank 2 Lean Shift Monitoring and P0308, misfire in cyl 8. It seems to be missing on more than one cylinder beacsue it has no power. The check engine light started to flash after a whle. I had to continue to drive the car. It was real difficult and took WOT much of the way in second gear. It felt like it was running on about 4 cylinders. The exhaust seemed to get real hot. It still starts and runs, but very poorly.

The outside temp was in the 90’s in some places, but the engine never went above 221 F. It always ran 196 F when moving on the highway. This was the first time the car was in hot temps this year with the A/C on.

Fuel pressure is 45 psi at idle and goes to 50 psi under WOT. Every cylinder has strong spark. Disconnecting the plug wires cause the spark to jump to the valve cover. Raised the fuel rail and every injector fires. Pulling the injector A or B fuse causes the car to run slightly worse. The coils/module, plugs, wires, thermostat, water pump, tires, and fuel pressure regulator have been replaced in the last 15k miles.

I did not do a compression test or headgasket test. The car did hard start cold at times and would sometimes miss cold even after all the above parts were replaced. The car ran excellent after 30 sec and all other times. It also ran 0-60 about 2 weeks ago in less than 7 sec.

Could a crank sensor cause this and would all 8 cylinders fire if bad? Could a headgasket case this? I rented a car to come back to NY, so the car is stuck in Atlanta. Should I have it towed to the dealer down there? Bring it back home to NY? If someone has an idea what's wrong about how much would it cost to fix?

Also thinking of putting it on ebay as-is. It is not worth much so I really don’t want to put a lot of money into it. It still looks great and everything still works (less the engine).

eldorado1
05-30-05, 07:28 PM
Hmm... That's a stumper. Everything's pointing to it's not getting enough fuel for some reason..... Does anyone know if cylinder 8 is in "bank 2"? Was the WOT fuel pressure test done on the road?

Ranger
05-30-05, 08:20 PM
No. 8 is on bank one (left bank).

LCLCLC
05-31-05, 03:00 AM
Badly leaking Fuel Pressure Regulator?

This does not support the 'lean shift monitoring' error?

But this would cause a cold start problem.

Concourson20s
05-31-05, 08:38 AM
If you want to let it go as is, I'm intrested. You can communicate with me if you like: g_vleazquez452@hotmail.com

Ranger
05-31-05, 09:59 AM
Badly leaking Fuel Pressure Regulator?

This does not support the 'lean shift monitoring' error?

But this would cause a cold start problem.
A leaking FPR would be more likely to cause hot start problems rather than cold start problems.

longisland516
05-31-05, 02:51 PM
The car has the problem at idle with the fuel pressure at 45 psi, so I think the FPR is working OK.

The car seems to be stuck in a "limp-home" mode. I think the fuel injectors were firing every other interval when I lifted the rail, but not sure. Is there any condition that could cause the car to enter this mode? Does "limp-home" mode cause the fuel mileage data on the driver display to be off by a factor of 2?

The fuel mileage did not decrease using WOT for the rest of the trip (about 500 miles). The driver information center was reporting around 10 MPG on the highway, but the car was actually doing over 20 MPG. This was really odd. The range indication was also very low, but the real range was much higher. The fuel used display indicated that 36 gals were used on one tank, but I only put in around 17 gals to fill the tank.

One dealer in Atlanta wants $112 to look at the car and $4600 to replace both headgaskets and timecert all bolts- with no warranty. He said they have a 95% success rate.

A dealer here in NY wants $133 to look at the car and $2645 to replace both headgaskets and timecert all bolts. The dealer here said I should see white smoke if the headgaskets are bad. The car never smoked at all at any time.

Ranger
05-31-05, 03:38 PM
Two dealers want to replace head gaskets, and they haven't even looked at the car yet? :rolleyes:

longisland516
05-31-05, 03:53 PM
To be fair to the dealers, I asked how much it would cost if that was the problem. I am trying to decide to fix it and if I do, where. It is much cheaper to have it trucked to NY and fixed here it seems than down South, not sure why. The NY dealer didn't think the head gaskets were the problem after they asked me if I ever saw any smoke and I said I didn't.

The Atlanta dealer thought the head gaskets were the problem after he asked me, "Did the car start hard when cold and run rough for a short period?" I said yes, it has done that for 2 years on and off.

fullserviceman
05-31-05, 04:41 PM
sure doesnt seem like headgaskets from what I hear I would shop repair shops for the answer, Up in Albany its $79 to diagnose at the dealer and prices of independants are cheaper on repairs.

Ranger
05-31-05, 10:06 PM
Since the car is down south, it might be worth the $112 just for the diagnosis. Might be something cheap and easy. Bad news is no other dealer up north will honor their warranty (I don't think). On the other hand, trucking it up north might blow any cost savings. Trucking it north can't be cheap. I think if it were me, I'd pay for the diagnosis and then decide if I could fix it myself or have them do it. You can always make the final decision after the diagnosis.

Concourson20s
06-01-05, 03:43 PM
I personally think your problem is no where near mechanically related. Sounds to me like you have an electrical issue: a PCM or possibly a BCM problem, either a malfunction, poor connection, or insufficient ground. An ignition problem, etc. I would do the diagnostic's systems check. Basically enter diagnostics, and check that all modules are on and active, all communicate with the IPC, all display required information, and obviously that no codes are set. Once thats clear, then begin checking all the powertrain electrical feeds such as loose or broken grounds, shorts, loose corrodided battery cables ect. Thats what I would do with the car in my hands, after i determine that the electrical, fuel/ignition systems are to specs, i will begin pointing a finger at the engine. But to say off the bat it's the heads, replace and thread chase the block is just rediculous. Thats a scam waiting to happen. I say you seek the advice of another repair shop, one that is known for electrical specialty.

longisland516
06-03-05, 10:44 AM
Thanks for the excellent information. The key to this puzzle seems to be the fuel data being off by a factor of 2 and the car running on (I think) 4 cylinders. I am trying to figure out how this could happen. It seems the cam and crank sensors feed into the IC module. The IC module also feeds the ECM with fuel injection control data derived from the cam sensor.

The only non-original electrical part on the car was the coil/IC module I bought on ebay 6 months ago. It was not a direct match for the engine and came with a note not to follow the coil to plug numbers and had a port plugged that I removed. This IC coil/module did not solve my original problem (hard cold start) and I just left it installed.

I sent the original IC module to Atlanta to "gun-shot" the problem. I will know by this weekend if this fixes the problem. If this doesn't work I think I am just going to have the car trucked back North and try to fix it myself.

I am looking at a 2000 STS to replace this car. It has 55k miles. Did Cadillac completely fix the head gasket problem when they redesigned the engine in 2000? I sure hope so.

Concourson20s
06-03-05, 04:05 PM
Yea the head gasket issue is solved however, nothing can protect a headgasket from any overheating issues, which are the headgasket issues we see on current day northstars. Listen I had an issue once with a 01 DHS. It had a very similar problem. Basically the IPC was not displaying the correct information. Fuel display was off by a couple of miles, the fuel sender would only mark to about 12 gallons then it would alert driver of low fuel warning. Also once on a test drive of about 4 miles the odometer jumped 10k miles. In the end I had to replace the bcm (body control module) and re-program. The culprit? A highly corrodied battery cable that ended up breaking the terminal off with the cable. It was replaced a couple of weeks before by me and the car was fine. Car was towed in when that occured. I believe that the poor contact of the battery cable on the battery with the car running caused excessive voltage spike which in turn fryed the BCM.

longisland516
06-03-05, 08:50 PM
“Yea the head gasket issue is solved however, nothing can protect a headgasket from any overheating issues, which are the headgasket issues we see on current day northstars.” How is this possible? I thought these cars could run without antifreeze and not overheat. How do they overheat? Do the head bolts pull through the block like the older Northstars during an overheat condition?

As far as my DeVille goes, the “quick-fix” did not work. I am having it trucked back North. So sad! The odd part about my fuel data is I think the BCM is 100% correct. I believe the car thinks it is firing all 8 injectors, so the very low MPG readout would be correct. Since (and this is just a guess) the car is firing the injectors every other time the real mileage is actually double.

The BCM calculates MPG, fuel used, instant MPG based on actual fuel injector pulse width, not by actual fuel used. In other words, the car thinks it should be using this much gas, but since the injectors are actually firing half as much it is getting double the gas mileage as the computer thinks. The timing diagrams are very complex in and out of the IC module so this may not be easy to troubleshoot. When I get the car in my hands I will do a compression test, check for vacuum leaks, and some other basic stuff first. If I am way off base please let me know!

Concourson20s
06-06-05, 10:10 AM
Let me rephrase that. They do not suffer from overheating issues. However most of the head gasket problems I've seen on the newer northstars has been because the vehicle was overheated. However that is the fault of the owners due to neglect. Because the vehicle warns you well in advance when there is trouble present. And common sense tells you not to drive the damn thing and get it fixed. I have only torn down 2 00+ n* and I did not have issues with the thread being damaged. I have heard of some but they were higher milage examples. One with 161k rental vehicle. I ran a thread chaser only to clean the threads, and of course used new head bolts. Any problems you have just ask, you have my e-mail I will try and help you the best I can.:thumbsup:

Ranger
06-06-05, 11:15 AM
Do a search for head gaskets and read up on what Bbobynski has to say about chasing threads.

longisland516
06-24-05, 06:24 PM
To make a long story short I had the car towed to the Cadillac dealer in Atlanta. The problem was clogged fuel injectors. It seem that I must had gotten bad gas in NC. The dealer tested injector flow and then performed injector flush/cleaning. The car runs great. The only item replaced was the fuel filter.

It took lots of abuse for 500 miles. These Caddys are amazing! A mechanic mentioned that diesel fuel mixed in with gas can cause similar problems after I explained a white grease like substance on the bottom of the injectors.

eldorado1
06-24-05, 06:31 PM
To make a long story short I had the car towed to the Cadillac dealer in Atlanta. The problem was clogged fuel injectors. It seem that I must had gotten bad gas in NC. The dealer tested injector flow and then performed injector flush/cleaning. The car runs great. The only item replaced was the fuel filter.

It took lots of abuse for 500 miles. These Caddys are amazing! A mechanic mentioned that diesel fuel mixed in with gas can cause similar problems after I explained a white grease like substance on the bottom of the injectors.

Good deal. Sounds like it could've happened to anyone.