Hotwire

Thanks, I have a vacuum hand pump that I can put on there and read the vacuum. I also heard there was a TSB for intake gaskets that were leaking from the inside. A GM tech on the s-seriesforum (my homeland ) told me to pull the oil fill cap and seal the valve cover w/ my hand to it to see if i had vacuum in the crankcase.

I will try all this along w/ compression test to see what i get. I'm sitting at home w/ a virus, not feeling too well, so I may hold off till this weekend to do everything. I hate pulling the plugs on the beyotch. If my wife came home and found me in the garage... whooooo

Here are the plats that i pulled the other night, they have about 300-500 miles on them. 1,3, and 4 look good, but all the rest are pretty much fouled. but this is also from just idling the motor, no load. i'll let you know what i find. ps, pic is about 800kb.

Injuneer

In closed loop, the O2 mV's should be jumping all over the place. The PCM corrects fuel based on O2 sensor feedback approx 9 times per second, swinging back and forth between slightly rich (14.65:1) and slightly lean (14.75:1) compared to the stoichiometric goal of 14.7:1. As a result, the O2 mV's should be jumping rapidly, with readings covering the range of 0XX-9XXmV. If its sitting relatively steady at 700-800mV, is isn't in closed loop, and its running way richer than its supposed to be at part load.

You are correct, when the sensors are cold, they can not generate any voltage, so you see the 450mV bias that the PCM supplies. As the sensors warm up, and with an AIR pump, the voltage will gradually drop to 00XmV, the coolant will get warm enough to kick it into closed loop, and the timer (2-3 minutes) runs out, and the O2 mV's start cycling.

96ZRDR

Hey guys is it normal to see 140 F on the IAT sensor right at start-up , with engine cold (sitting for more than a day). This seems impossible to me. The air must be cold at start-up, but then again I do live in Hot and Humid TEXAS.

What does your IAT sensor read Hotwire, I believe my ecm adjust fuel in accordance with the IAT sensor tempature. Higher temp, more fuel. Anyone?

Hotwire,

Are you still using your stock #24 injectors? Your plugs look indentical to mine. Are you trowing any codes other than the knock sensor. Fix your knock sensor, I believe it retards 8 to 12 degress at all times if the your pcm does not see it.

96ZRDR

Injuneer,

I dont believe any one of us use has an Air Pump, so is it safe to say that the 0'2 will not cycle down to 00xmv without one. It this safe or part of the problem (not having an air pump) my 0'2 do not cycle down, they cycle up.

Also a longshot but probable,

On my 93, could it be that my ecm forces closed loop conditions even if the sensors are not hot enough to spit out correct information. Or does it somehow read 0'2 tempature? i dont see how, since there is only 1 wire coming from them. Does not the ECM just assume the 0'2 are ready for closed loop conditions once the timer counts down, and coolant temp is hot enough? All I know is that my car will not go into closed loop condition in idle at all, but it happens almost immdiately after I put it on load (on gear).

?????????

thanks

Injuneer

Even without the AIR pump, the sensor voltage will slowly drop as they warm up. Once they are warm, and it kicks into closed loop, they should cycle above and below 450mV, with extremes in the 0XX and 9XX range. This is "normal".

If the ECM sees a steady 450mV, it isn't going to kick into closed loop. It can not measure the temperatures of the O2 sensor, but it looks for "activity".... values departing from 450mV.

Your sensors are not warming up. The one-wire unheated sensors have that problem, when they have been relocated further from the engine. A few of the 93 guys have converted to 3-wire heated sensors to solve that problem.

As far as the IAT, when the engine is "cold" (e.g. sitting over night) turn the key on, but don't start it. Coolant and IAT should be almost the same as the ambient outside air temp. If you see 140degF, there is something wrong with the sensor or the wire.

Yes, in a speed-density 93, the ECM used pressure (MAP) and temperature (IAT) of the air to calculate air density (pound/cubic foot) of the air, then it multiplies RPM X volumetric efficiency X density to calculate mass air flow... then it adds the amount of fuel required to match the mass air flow it calculated.

95 Silver TA

Hmmm. Thats wierd,

Mine cycled up before the blower and 383 Swap but I did not have the airpump on it, and after the Blower and 383 Swap (still no Airpump), I replaced the o2 sensors with 2 new ones from AC Delco and it still does the same thing (cycle up). I got it tuned with the 50# Injectors, and it still does the same (cycle up).

Does it matter?

Thanks,
Claude

Hotwire

Like Fred is saying, mine are all reading ambient temperature. Last night when I fooled with it, it was sitting at 72 degrees. I know if you pull the plug it will read -40, that's where my dtc 15 came from (water pump laying on garage floor).

Check your iat sensor. scan your sensors, watch the iat. it will read 140 degrees, pull the plug, should go below -30 degrees. if so, replace it. if not, check the tan wire back to your pcm for shorts, or could be the pcm. (straight out of 94 helms manual, not me.) Should have about 5 volts on the tan wire w/ the ignition on. hmmm... also check your ground on the sensor to make sure it's getting connection to the pcm.. it is shared w/ the map sensor.... might lead to something...

my tps is reading .68 - 4.65 volts, never hits 100% throttle angle. is this normal, or should I replace it as well?

I have no codes at all, but my ses light is staying on, i have to check my wiring. I have the knock sensor dtc 43 and the low coolant sensor leve dtc 15 stored in the history codes. I know why knock sensor dtc is there, and the coolant dtc is from when i was running the truck when i first got it running w/o the sensor hooked up.

I am running stock injectors, never touched as far as i know.

man, if the truck was running the way it was w/ the ignition retarded that far, can't wait to get it on the road w/ the right knock sensor on there!! Holy #($&(#&$!!!!!!

96ZRDR

Hot Wire,

Let me get this straight, at startup with IAT hooked up it should read 140 off the bat? Without it hooked it should read -30?

If so, then is this bad? 140 is not where is should be I think?

Hotwire

no, it should read the temperature where the car is parked. it's reading the temperature inside the air duct. it's like a thermometer in the duct.

if it's reading 140 off the bat and it's 140 outside, then yeah, it's fine. lol. if it isn't 140 outside, you have problems. do the check like I said above.

if the readin is 140 off the bat, disconnect the iat w/ the ignition on, if the reading changes to BELOW -30 degrees, then the sensor is possibly bad. Also check the voltage on the tan wire, should be +5volts, and black should be a good ground. If power and ground are good, replace the IAT.

96ZRDR

Wow, good information, at least now I got a new lead.

Thanks Hot wire.

I will post my results.

Injuneer

You can test the temperature sensors by measuring the resistance at known temperatures.... e.g. 32degF in ice water, 212degF in boiling water. There is a table of temperature sensor resistance vs. degF in my ScanMaster writeup. Also a lot of info on the "normal" readings from a lot of the other sensors.

96ZRDR

Update:

I checked my IAT sensor tonight, with ignition key on (engine off) it read 150 Degrees Farenheit,.................with the sensor unplugged it read 350+ Degrees Farenheit.

Is this normal????? I pulled out the IAT, and it has the following part number 12110319, is this right for a 93 Lt1? I looked at my buddy's 94 and it had the same part number. I think they are diffrent though.

Anyways, I asked my brother to purchase a IAT sensor from our local autozone but I have not yet been able to test it.

Thanks

Hotwire

That's not right, it should be reading a negative temperature w/ the sensor unplugged. Did you check to see what the voltage was on the tan wire? I'd trace that wire back to the pcm to see if it's getting shorted out to something.

Measure the resistance of the IAT like Fred was saying to see if it's reading right. Man, we have to get out of this plug and play scenario. lol.

have to take my little girl to see hulk tonight.. but will have my knock sensor and intake gaskets ready so in the morning I will do compression test, check for vacuum in the crankcase, and hopefully find a leak or something.

good luck.

96ZRDR

Update:

Hey guys just got done checking the ohms on my IAC sensor. I reads fine, give me about 1650ohms which translates to about 90-94 deg Farenheit. which sounds about right.

I also checked the voltage out the the tan wire from the ecm, and it read 5 volts +/- .10. That seems right also, but when I scan, it show 140+ Farenheit still. When I unplug it reads the same 332 Deg Farenheit as it used to before.

Could it be the ground wire. How do I check that?

Hotwire

Try putting one side of the ohm meter to the engine block, and the other to the ground wire, see if you get any resistance, or a negative reading (voltage on the line). If that looks ok, try going from the case of the pcm to the ground wire. Try both w/ the ignition on and with it off to see if that makes a difference either.

I might have found my problem.. ok, #4 is the cold primary while it's running, right... well, ALL the cylinders I can get to are reading about 198-202 psi on crank up compression (engine cold) even #4, except for #3, it's reading 166 psi. wtf?

I reckon I am just going to bite the bullet and pulls the heads, possibly sell some stock and just build the motor. really sucks, wanted to baseline it before I did anything to it.