New to Buick and this Forum, some help please..

[88PA]

I recently started driving my mom's 88 Buick Park Avenue as she had a stroke and will probably never drive again, bless her heart she's a trooper.

I have known that the service engine light was on for a long time and when I would suggest looking into it she would tell me not to worry about that let's have coffee and visit instead. I guess the dealership ran the codes and somehow it was settled that she would just drive the car with the service light on so she has for a couple years.

The car runs pretty well, idle's a little rough and has died a couple times while going from reverse to drive in a parking lot, can feel some jerking at idle. Ran the codes (paperclip style) 13-open ox sensor, 41-cam sensor, 48-misfire. I then cleared the codes, started the engine to idle for about half minute then shut off and rechecked and 41 was the only code that flashed. Logically I would go to the cam sensor, I have heard that the 3800 is notorious for the little magnet coming out of the socket. My question is: Will this engine run at all if there is a problem with the cam sensor? Will it run if the magnet has come out and the sensor is no longer working? I hope it's just a loose wire, I haven't started actually wiggling stuff yet, wanted to get some info first.

Thanks for any help.

[Blue Bowtie]

Welcome Aboard!

First, best wishes to your mother.

As for the question at hand, the '13' will likely resurface once the engine is at operating temperature and the ECM is in closed loop mode. You can (and should) check the connection to the O² sensor, but there is also a chance that the sensor is contaminated or weak. The '88 used a one-wire, non-heated O², and those tend to have a shorter service life. Fortunately for you, if the sensor is weak, a replacement can be had for about $20. The fuel savings alone can quickly pay for that. If you're lucky, it may only be a fouled connection.

You are correct that some of these engines can lose the magnet from the cam sprocket after time. That can be checked reasonably easily with a bi-directional scanner or a reasonably fast voltmeter or oscilloscope, since a missing magnet would mean that a CMP signal would never be generated. If using a scanner, even if the signal is "missing" it is best to verify that with a meter or 'scope, since the scanner is only reporting what the ECM sees, and not a direct reading from the sensor. If the signal is weak or intermittent, that would indicate that the magnet is likely intact. Magnets can be replaced, but that requires removal of the cam sprocket (no fun). An intermittent signal can be caused by contamination on the sensor face, contamination on the magnet, poor connections, or an electrically failing sensor.

The ignition system on your '88 may be the early version of the Buick "Fast Start" system. With this scheme, the engine will start and run with a bad CMP sensor, but usually after protracted cranking. The fuel system will run in batch fire mode as well. With an intact array of sensors, the engine should fire and run within one crank revolution, and usually considerably less.

The misfire error could be related to either the O² or the CMP (or both). Solving the CMP sensor problem may clear that, but probably won't eliminate the '13' error. Lacking an O² sensor signal, the ECM will revert to Backup Fuel Mode, which is typically rich (about 13:1). The ECM may also be limiting ignition timing as a result of a lost sensor signal, causing even less performance and mileage.

[88PA]

Thank you Blue Bowtie for the help! I understand what you are saying I should do by looking at the sensor output using a meter or Oscope but I haven't the foggyest idea where to connect to it.
I did however take the time this morning to inspect for the magnet and it is there, I cleaned it and the sensor up but still getting the 41. I may just go buy the sensor at the zone tomorrow along with an 02 sensor.

Can anyone point me in the right direction for Cam pos. sensor hook up under the dash so I can look at it's out put with a meter?

Is there wiring schematics/diagrams somewhere online?

Thanks

[Blue Bowtie]

The CMP should be wired directly to the Ignition Control Module (ICM), and not the ECM. The ICM conditions the signal and sends it to the ECM. The CMP and CKP can both be tested right at the ICM, out front of the engine. If the sensors themselves test good, suspect the electrical connector on the front/lower edge of the ICM base. It is somewhat prone to moisture incursion after 20 years, and could be corroded.

[Blue Bowtie]

[88PA]

This is a wealth of information! Thanks, I will post back with what I find.

[88PA]

Well, here are the results of my test.
Referencing the above wiring diagram this is what I found using a Fluke 8060.

To check the Cam sensor I used Cam sig. in- M&J at the ICM connector, 136 Hertz and about a third of a volt, Freq. increased with speed.

To Check the Crank sensor, Crank sig. in- M&G 317 Hertz, no voltage even in the MV scale. Sync sig. in- M&H 60 Hz increases with speed, small amount of voltage.

I used sensor gnd M on both.

It seems like I hooked up correctly and that both sensors are working but, I wish I knew what a good reading would be verses a bad reading (any thoughts?). I also checked terminal F with reference to sensor grnd M and had 47 to 55 Hz, small amount of voltage.

I tried to remove the crank sensor to clean it but it wouldn't come loose, do I have to remove the Harmonic Balance wheel to change this?

OK, did I test these sensors right or do I need to do something different? All tests were at idle speed unless I sped up the engine by hand.

Thanks again for all the help!

[Blue Bowtie]

If you use an 8026B, you'd be able to read true RMS voltage (but not frequency). At idle RPM, you should read about 400 Hz at the cam sensor and about 2K Hz at the crank sensor. The P-P voltage will be about 5, but the RMS would be really, really low. You can performs the check about the same way you did, with the POS lead on the BRN/WHT wire (J terminal) and NEG lead on the RED/BLK wire (M terminal).

When checking the cam signal output (F terminal) reference the meter to the K terminal (signal ground).

You should also meter resistance or conductivity between the K, L, and M terminals. The ICM is grounded only through the base, and corrosion and decomposition of the heat sink compound on the base and its fasteners can prevent a good ground, and therefore, good ignition signals. I've had a few of these for which I've had to remove the coil packs, ICM (module), and scrape/polish the base to get a sufficient ground, after which all problems went away. Don't forget to apply a fresh, thin layer of heat sink paste to the ICM/base when you mount the ICM.

And when all is well with the ignition system, you're still likely to have an oxygen sensor error.

[88PA]

The meter is an 8060A and does read Hz but I not sure it will read KHz. I'm going to hook up a Fluke scope meter tonight and see if I still only get 130 Hz on the cam sensor. If so does this mean it's bad?
Thanks

[88PA]

I think I may have a bad cam sensor. I put a Fluke 105 scope meter on M&J and got nothing at all. I went to the crank M&G and had 342 hz. I then checked F with reference to M since there is no K (there isn't a place for it so it was never there) and got a big fat 0000hz.
The magnet is there so that just leaves the sensor.

If a cam sensor don't fix it I'll pull the ICM off and clean it up.

I think the Fluke 8060A I was using was reading some induction from the alternator.

[wrightz28]

Originally Posted by 88PA

.
The magnet is there so that just leaves the sensor.
.

And the wiring (wich is subjected to quite a bit of heat)

[88PA]

Yea, I know. It won't supprise me a bit if after putting a new sensor in I still have the light but my test results seem to indicate a bad sensor OR wire

I guess I will only iliminate a possibility by throwing 20 bucks at it. Who knows, it just may fix it....

[HotZ28]

Originally Posted by 88PA

The car runs pretty well, idle's a little rough and has died a couple times while going from reverse to drive in a parking lot, can feel some jerking at idle.

Before wasting hard earned money on a CPS, disconnect the wiring connector and see if it will start & run. It should, however, injector timing will be out of sequence and will cause a slight stumble & some hesitation. Remember, code 41 can be either the CPS or the CKPS!

[88PA]

Well, I think I found the problem. It was the magnet after all. I went and purchased a new Cam sensor today, put it in and still had the light. I had tried running the car with the CPS unhooked and it made no difference so I assumed it was this sensor.

Baffled, I decided to have another look at the magnet (interupter). I needed a better mirror so I raided the wifes makeup stuff and wound up with a good clear view of the magnet. The holder is there but the magnet is long gone.

I went and got me a new interupter and some JB weld, I'm going to try the easy install. I'll post back with the results, unless I'm incapacitated from the wife discovering her mirror is gone.

[HotZ28]

Originally Posted by 88PA

My question is: Will this engine run at all if there is a problem with the cam sensor? Will it run if the magnet has come out and the sensor is no longer working? I hope it's just a loose wire, I haven't started actually wiggling stuff yet, wanted to get some info first.Thanks for any help.

I had tried running the car with the CPS unhooked and it made no difference so I assumed it was this sensor.

I'll post back with the results, unless I'm incapacitated from the wife discovering her mirror is gone.

I hope you didn’t break her mirror!
BTW, whether you know it or not, you just answered you first question in your post, and confirmed our gut feeling. This is an important contribution! The 1988 model LN3 3800 engine will run without a cam position signal, resulting in stumbling & hesitation off idle. Lack of cam signal, can be either the cam position sensor, magnet damaged, or missing magnet.