how to tell if cam position sensor

[spunger]

I was reading some posts about the cam position sensor and it going out. I was curious, when I hook my autoxray up to it, it goes between not detected and detected. Is that normal? Please let me know.

[spunger]

ttt

[strange_trp]

the cmp is used to synchronize sequential fuel injection. it is a hall-effect sensor. the best way to test hall-effect sensors is with an oscilloscope or other automotive analysis tool with at least 1 channel for DSO and time scaling to at least 500 msec (is okay for cmp. to check ckp you want time resolution of around 50 msec or better). you want to see very regular square waves as the engine is cranking over. if not, verify proper supply voltage and circuit continuity. if sensor ground and signal and supply wires to pcm are intact but you get erratic signal trace on the scope, replace cmp sensor.

other than what you're seeing on your scan tool, is there any reason you think your cam pos sen is going bad/ gone bad?

[spunger]

thanks for the reply

No, my car has a sorta funky idle unless I let it warm up which makes me think it's my o2 sensors. Say if I start it in the morning, and try driving right away, the car surges from 700-1100 rpms and goes back up and back down for a little bit until things warm up, and once they are warm it is ok. I have replaced the EGR (emissions reasos) and the IAC (idle air control) sensors. The o2 sensors haven't been replaced to my knowledge. Just the idle gets to me sometimes.

Thanks again,
Chris

[strange_trp]

what you are describing would not likely be caused by faulty O2 sensors, and its not really all that likely to be caused by faulty cmp sensor based on my reading of your description of the problem.
i would test MAP, MAF (3800), ECT sensors to start with. may also be a problem with canister purge solenoid or vac lines to evap canister but not really likely... hard to say without looking at some scan tool stuff and gathering more info...

hunting idle when cold, goes away when warm... i'd say definately not O2 sensor.

[spunger]

Ok, well I wonder if my vaccum line from the MAP sensor is cracked or retarded. Map sensors aren't much anyways, but any solid way of checking it with my autoxray or voltmeter?

[strange_trp]

you may check map sensor with either. best to check with both to compare results...
got a vacuum pump??? you'll need one to do this test.
apply about 20 inches vac to the sensor with sensor plugged up and ign in "run" (engine off). look at scan tool and MAP value should show about 9-10 in hg or so. as you release vacuum on the sensor, the scan tool MAP value should rise to almost 30 in hg (atmospheric press) with no vacuum at all on the sensor. apply vacuum, you should see MAP value drop at a linear rate.
you may also disconnect sensor and check for 5v ref across the grey and onr/blk wires (well these are the colors for a 99... yours may or may not be similar... just put dvom probes on 2 of the 3 leads and see what you get. you won't hurt anything unless you cross your leads to short the ref voltage circuit... you should get 5vdc across 2 of the terminals)

good idea to check/replace vac line going from intake manifold to MAP sensor.

[ May 09, 2002: Message edited by: strange_trp ]</p>

[spunger]

I will check that sensor out this weekend. I wish I could explain my idle more. It is the weirdest thing.

I got my car in june of 2000 and drove it fine until christmas time of 2000 when the head gasket blew. Everything was fixed and put back, and I have been driving it sense without any problems what so ever. Car works like a charm. Except for this weird idle problem.

I think ever since it was rebuilt this has happened. The idle was too high, and would surge up and down, and idle at like 1200 rpm. The entire time the car would go up and down, up and down while idling. I took my car to get smogged and found that the EGR and the IAC valve were bad. I would get EGR SES lights for a while. Ever since I changed it out I haven't gotten any codes since.

My idle changed down to 700-800 while idle. The computer says "suggested idle" and then accual idle, it is within 10 rpm so I go great, that is good! Once the car goes into drive, it will surge or dip up and down a few hundred rpm's. Sometimes it goes so far as to almost staling, but it hasn't ever done that yet.

If I let the car warm up for like 5 minutes, (no exaderation, full 5 minutes) then it doesn't happen, or if it does it doesn't happen as bad. If I start the car, and a couple minutes later drive, it will surge and dip until it is warmed up. I have thought that my O2 sensors might be bad since my gas milage is starting to bite the dust. I also thought it may be my camshaft position sensor because it reads "detected, not detected" but I dunno if that is the problem. All these sensors are like $30-40 each, so I don't want to go buying too many of them.

I use to think it was when I would apply my brakes the diping in rpm's would happen. Turned out afterwords it was just when it was in drive.

Any further help would be great!

Thanks,
Chris

[strange_trp]

applying the brakes as well as shifting into "D" are both ways of loading the engine. this problem sounds like either bad map, bad ect, or perhaps vacuum leak. possibly also canister purge problem.
what is your map reading at idle?
how does the ect look? watch it warm up from cold idle, then steady off and turn down some as the thermostat opens. as the car just sits there idling, it should reach and remain around 180-210 degf, regardless of what t-stat you have (manual fan switch off, let pcm control fan operation.) watch for significant changes in load sensor parameters, as well as a significant change in the calculated load %.
many things can cause poor fuel mileage, but a bad O2 sensor will not cause what you are describing. unless its just never going into closed loop operation plus you have a vac leak, bad map, ect sensor, etc...
if you have PC Link with your autoxray, record some data for me and email me the file so i can see what is going on.

[spunger]

I have changed that sensor too, the ECT (engine coolant temp) right? I changed that out a while ago and it seems to be working fine. I think I am going to aim and watch the MAP sensor and look for some vaccum leaks. I think that is all I have to look for.

I do not have the PC link for my auto xray, but I will hook it up tomorrow morning and get some readings from the map sensor, try to take notes for like 5 minutes watching it and seeing what it does. I'll also watch some other things and report back.

Thanks for helpin me,
Chris

[strange_trp]

don't mind helping at all, my f-body friend.

best to test a part's operation rather than throwing parts at a problem... measure twice, cut once, my high school woodshop teacher used to say (right before he let us leave campus an hour early... i loved those days [img]smile.gif[/img] )
post as much data as you can, as well as how the data changes as the engine warms up and the idle steadies. i know that on the 99, the "unenhanced" (no upgrade) version of the autotap will give you like 26 values and the gm enhanced upgrade opens up about another 30. some are very useful (watching O2 response compared with ST and LT trim on the graphs with PC Link), ECT, TPS, IAC position, calculated load, RPM, MAP, and loop status. just to name a few. the reason i wish you had pc link is so that i could see graphs over time of how the sensors started responding to things... i could tell you to do A,B and C while logging with the autotap and you could send me the file... oh well, we'll make do with what we've got. post or email me and i'll do what i can to help.
i love this drivability stuff. its what i poured all my attention to while working towards my AAS degree in automotives (walking in May, i'll get the actual piece of almighty paper this august when my credit by exam goes in for my last course.) i love dealing with electronic engine controls, but i have zero opportunity to work with them at my current full-time job (blah... sears auto center... i'm a senior tech there so i can kinda choose what i want to do but the job still sux.) but i teach this stuff at the local comm college part-time at night and this site (and side jobs i do) are really the only chance i get to do a lot of this kind of diagnosis.
it makes it even more challenging diagnosing these problems hundreds of miles away... i love it.
so post or email... if you do post, you may want to email anyway because i sometimes dont get a chance to post all that often... hopefully that will be changing soon... we'll get it worked out. you will need your scan tool, a DVOM (digi volt-ohm meter, and knowledge of its proper use like doing voltage drops, etc... i'll explain if you don't know...) a vacuum pump/vacuum gauge, and some other odds and ends stuff. the tech2 would help us greatly but my only access to one is through the school and i'm not about to shell out a few thousand bucks for a gm-specific tool (although it does a hell of a job with gm diagnostics... shift from 1st to 3rd with auto trans and the line press jacked up to max? i can do that... [img]smile.gif[/img] diagnostic purposes only, of course... )
keep me informed on things, bro... it will be after 10 tonight before i'm back online...

[ May 10, 2002: Message edited by: strange_trp ]</p>

[spunger]

I hooked up the old autoxray and did some testing, about 9 a.m. Probably 60 degrees outside. Started it up and watched the MAP sensor voltage. Started off at like 1.4 volts (ranged between 1.4 and 1.45). When I started driving, and the idle went and did it's dips, the voltage didn't seem to change much. Went as high as maybe 1.55 volts. The barometric pressure stayed at 4.90. While driving the MAP sensor went almost as high as 3 volts, but never got there. Highest I think I saw it jump to was 2.85 volts. Then it would go back down to high 1 volt ranges (1.7-1.89) and all in between. All at this time, the Mainifold air stayed at 66.5 degrees. It went up to a high of 68. When I parked the car, the MAP was at 1.43 volts and going between 1.43 and 1.49. That was just watching the MAP sensor.

I can watch just about any sensor and record back. If I have to get this PC link, no problem, I'll find it and buy it unless it's super expensive.

The entire time, the autoxray reads 13.6 volts from the computer, and fuel pump voltage stays the same (13.6). I was told not to worry as everything is regulated. My battery charges at 14.4 (hehe stereo tells that truth) and even if I use my multimeter at the battery it is charging.

I was just reading through some of those. Idle Air Control valve reads learned 28 steps, and starts off at like 47 and makes it's way down to 28. Engine coolant temp sensor starts off at 66 degrees and works it way up to 160.

If there is anything else you want me to check let me know.

Thanks again,
Chris

[strange_trp]

map values look okay, although they might be just a little high at idle.
check intake manifold vacuum at idle with vacuum gauge or gauge on hand-held vacuum pump.
are you going into closed-loop?