Rough Idle

[thunder57]

First off, I put a 91' 4.3L S-10 motor into my 88' full size, the original engine was running on 5 cylenders and ran like sh*t. So I found a good running S-10 that was rotted out and ran good. After the swap I ran into some problems, all the original pieces on the 88 motor I put on the newer motor, and it runs rough. I have already checked the fuel pressure and the MAP sensor. I did this by take my map Sensor off and putting it on my dads truck ('89 full size) and it ran normal. I was told to check the 02 sensor and the CTS and TPS sensors. Could I get some help in doing that? Any other advice? Thanks a lot guys.

Jake Martens

[BlazinLow_inORE]

a little info from..
http://www.kemparts.com/scripts/140.asp

THROTTLE POSITION SENSORS - 141-Series
http://www.kemparts.com/scripts/141-7011.jpg

WHAT THEY DO
A Throttle Position Sensor is a variable resistor with a voltage output of less than .5 volts (when the throttle is closed) and 5 volts (when the throttle is open.) The amount of voltage sent to the computer varies depending on the throttle angle. The TPS is used on both fuel injected and carbureted systems.

FAILURE SYMPTOMS
A failing TPS may trigger a "Check Engine" light and symptoms such as: loss of power; poor fuel economy; hesitation; surging; engine "pinging", and no torque convertor lock-up.

MAINTENANCE/SERVICE
KEM suggests inspection of the TPS every 20,000 to 25,000 miles or at every tune-up. Refer to a Mitchell or OE service manual for test procedures and specifications. If the TPS tests outside of the required specifications, it should be replaced. Check for corrosion at electrical connectors, proper voltage output, smoothness of operation and possible sticking (a sticking TPS can cause the throttle to remain open.) Caution, do not attempt to lubricate the TPS.

LOCATION
The Throttle Position Sensor is mounted on the throttle body or carburetor and is connected to the primary throttle shaft.


OXYGEN SENSORS 138-Series
http://www.kemparts.com/scripts/138-108.jpg

WHAT THEY DO
This sensor detects the oxygen content in the automobile’s exhaust gases and sends a low voltage reading to the computer. This signal varies from 0.1 to 1.00 volts, depending on the amount of oxygen present. A high voltage signal indicates a rich air/fuel mixture, a low voltage indicates a lean air/fuel mixture. The vehicle’s computer constantly monitors this signal and makes any necessary adjustments to maintain the proper air/fuel ratio.

FAILURE SYMPTOMS
A faulty Oxygen Sensor can produce poor fuel economy - gas mileage may be reduced up to 30%, and other driveability problems associated with overly rich fuel mixtures. The “Check Engine” light will be on intermittently.

MAINTENANCE/SERVICE
KEM suggests replacement of the 02 Sensor every 30,000 miles or at every tune-up. It is necessary that the catalytic converter also be inspected - a bad Oxygen Sensor can cause premature converter failure.

LOCATION
The Oxygen Sensor is located in the automobile’s exhaust system.

FEATURES AND BENEFITS
Tailor-made Oxygen Sensors form a weathertight, corrosion-proof termination with prefitted connectors - for easy installation. Platinum zirconia activating tip provides precision-performance and extended service life. Stainless steel protective shell protects the sensor from damaging exhaust stream elements. Roll-crimp sealed components ensures a positive, airtight seal. Universal 138-108 Butt-type connector with heat-shrink tubing forms a weathertight, corrosion-proof termination in minutes - for all single wire applications.



COOLANT TEMPERATURE SENSORS - 140-Series
http://www.kemparts.com/scripts/140-740.jpg

WHAT THEY DO
The Engine Coolant Temperature Sensor (ECT) is a thermister, (heat sensitive variable resistor) that registers varying resistance in relation to coolant temperatures. When coolant temperature changes, the ECT’s resistance reacts and sends the automobile’s computer a varying calibrated electrical signal. The computer uses this information for adjusting idle speed, air/fuel mixture, open-closed loop computer status, evaporation canister purge and injection switching systems.

FAILURE SYMPTOMS
A bad ECT will cause poor driving performance, fuel economy problems and hard starting. Watch for service flag or “Check Engine” Light. Two common causes for failure of this sensor are coolant system overheating or a break in the resistor’s element.

MAINTENANCE/SERVICE
KEM suggests inspection of the ECT every 12,000 to 15,000 miles or when servicing the cooling system. It is necessary that the proper coolant level be maintained to ensure proper calibration of this sensor. Refer to the Vehicle Manufacturer’s test procedures and specifications. If the part tests outside of the required specifications it needs to be replace.

LOCATION
The ECT or CTS is located in the cooling passages of the engine block in most vehicles.

[BlazinLow_inORE]

http://www.wellsmfgcorp.com/counterpoints/counterpoint2_1.pdf#search='how%20to%20check%20tps %20sensors'

^^^ tells how to do a quick check on TPS
(adobe reader required)

[thunder57]

Alright, I'll have to get a multimeter then, how would I test the O2 sensor? would the positive go to the sensor wire then the ground be grounded? How often do TPS sensors go? Thanks for the help.

[Maximus]

If you don't car Blazinlow_inore I would like to use those pics and info and put it in a tech write up.It wouls save me the time of having to wrtie it all up myself and those ore pretty good write ups.I guess the sight they came from should get credit too if used.I might look in to this further.I was gonna just copy and paste from my Mitchell on demand auto repair disks but the pics on it are not to good.I wanna do a write up explaining all OBDI and OBDII systems and sensor theory and operation.But don't wanna inpose on any copy right protection.I know some of the disk info on my Mitchell disks are copyrighted but some are not.I am just gonna think this over more and see what I can do.Anyway thunder57 is the rough idle throwing a code.Is it just a rough idle or a miss at idle and under throttle.I need a little more info on the problem.Did you check the ignition system for any problems too.Like the timing,plug wires,coil,plugs and so on.

[BlazinLow_inORE]

max.... u might wanna check with the site... i listed the link with the info... so i was not being an *** and just saying here... this is my idea of it. lol... i gave credit so check with them

[thunder57]

I have changed the Spark Plugs(Bosh +4), Wires, Rotors, and cap. I have not tried adjusting the timing yet. My truck used to have the SES light on... it stopped recently, put the problem is still there. It only runs rough when it is warm, at stop lights in town it gets realy bad, almost stalls. When I rev it it runs good, and it recently passes emissions... Is this wierd or what?

[Matt 4.3 TBI]

First of all, I would recommend using stock AC Delco spark plugs. I tried the +4's a few years back and they fouled after about 3 weeks on a stock engine. In my experience the AC Delco CR43TS and RapidFires perform the best (I haven't tried any of the iridium plugs, though).

Your symptoms sound like mine after the rebuild, but I can blame it on the cam! If it runs rough when it's warm, it sounds like a closed loop problem. I'm suspecting the O2 sensor. Is it running rich or lean? If you have it parked and idling, it's pretty obvious from the exhaust smell if it's running rich.

You can check the O2 sensor by putting positive to the sensor lead, and negative on the sensor body (it is grounded through the exhaust) or any good common ground. TPS may not be bad, but it may be out of spec. The older sensors with the flat three-wire connector are easy to adjust, but the newer round-connector units need some cutting with a dremel or Xacto before you can adjust the output.

Make sure you check the timing, if you haven't already. Don't forget to unplug the ESC connector (it's under the passenger side dash in S-series, not sure about the fullsize). If all else fails, you may want to adjust the idle. There is a Torx screw in the front of the TBI unit right in front of the throttle lever. Let me know if you get to this point, I'll post up info on how to adjust it.

[thunder57]

Well first I thought it was a vacuum ball problem, because the full size engine that was in there used that spot for the transmission. So I ran it warmed and had the hole half open, it ran quiet a lot better. So I guess the vacuum leak was causing it to lean out, so it is running rich? Alright I'll check these sensors soon, thanks for the help so far.

[Matt 4.3 TBI]

Voltage for the O2 sensor is between 0.1 volt (high oxygen, lean mixture) and 0.9 volt (low oxygen, rich mixture). Keep in mind it won't produce proper voltage until the sensor has been warmed up by the exhaust. While idling it should be betwwn 0.35 and 0.55 volts, and it will bounce back and forth from rich to lean. Trouble is when it stays more toward one end of the scale (bouncing from 0.8 to 1.0 volt (rich) or 0.08 to 0.2 (lean).

[thunder57]

Well I tested my sensor today, I unpluged it from the wire and stuck the positive wire from the multitester and grounded the other wire. My reading were from .179 to .22 and sometimes .357. So should I just jump in and change the sensor... or should I check some other stuff so the new one doesn't just "foul out." Is there any way to "fix" the old one?

[Matt 4.3 TBI]

It's reading 0.1-0.3 volts? What range did you have your multimeter set to when you tested it? When I was tuning it would peg so rich it would struggle to keep running, and it was only at 0.1 volts.

Go ahead and pull out the sensor and look at the tip. Thick black soot will indicate a rich condition, dark brown indicates burning oil, white or red can be bad fuel additives (**** oxygenated gas) light tan deposits are coolant leaks.
You may want to replace it, as OBD1 one-wire sensors aren't too expensive (about 30-40 for a Bosch replacement), but I would hold off until we're sure what's causing the rich condition.

[thunder57]

The multimeter was in the DCV range and was on 2, I can take a pic of it if you wish. I'll pull the sensor tomarrow and see. If it is running lean why would it use so much gas? It uses at least if not more then my Dad's '89 305..

[thunder57]

Well I took it out, it looked black, maybe you could tell by the picture. But anyways the sensor is from when I had my old engine in there, it burned a lot of oil because the engine was gone and only had one bad cylender, so that might make it go bad?