Daily driver issues

34ford · August 05, 2011, 07:47:38 PM

My wife's 1993 Chevy Lumnia Z-34 does not want to keep running when started. It starts then quits starts then quits. She was stranded the other day and when I got there it started up right away. Thought it might have been vapor locked cause it was very hot that day. It has never vapor locked in the 15 years we've had it.

So today she calls me and says it's doing it again. I tell her to turn the key off and push the accelerator pedal 5 or 6 times. Tries to start it and it startsand runs great.

Could this be some type of sensor in the throttle body or another type of sensor

Has the 3.4 DOHC motor.

thanks in advance

wayne petty · August 05, 2011, 09:42:36 PM

could be carbon on the throttle body bore..

could be carbon in the idle air control passage...

could be a worn out idle air control motor..

could be the throttle position sensor..

do you have access to a OBD1 scan tool to plug into this system..

i have some chart that might help..

you might also have a problem with the air flow meter..

all these can be sorted out my looking at the live data stream...

after a visual inspection for vacuum leaks.. including loose plastic hoses..

and a possible bad power brake booster.. they can leak massive amounts of air and cause the engine to stall.. and the next push of the brake.. it might work ok..

wayne petty · August 05, 2011, 10:04:32 PM

after inspecting the throttle body bore for carbon on the throttle blade.. and in the bore.. and cleaning it out..

brake cleaner sprayed on a towel and the throttle held open and wiping it out..

sensor voltage to look for...

TPS.. Under 1.0 volt at idle.. above 0.35 volts.. a smooth sweep to about 4.5 volts when the throttle is slowly opened and back to the closed setting exactly.. one thing.. the TPS voltage has to come back to the EXACT same voltage . everytime the throttle is closed.. when the throttle shaft wears. the throttle blade can close to a slightly different angle.. causing the TPS to read different each time it closes.. fooling the computer that the drivers foot is still on the gas pedal when it actually is NOT.. this keeps it from reverting to the idle program.. and making problems.

next look at the IAC... idle air counts.. 20 to 50 at idle is proper..
this is how many steps back from closed the idle air control motor has positioned itself ..

if you get higher than 50.. or lower than 20.. you might have something wrong..

look at the coolant temp sensor readout.. on the scan tool... not the dash board... same as ambient with the engine stone cold.. 190 to 228 with the engine running .. the cooling fan cycling on and off..

with the engine up to temp.. look at the MAF.. 0.6 grams is a normal place for it to idle at.. it also should have a smooth read out as you raise and lower the RPMs slowly.. there have been problems with some models when too much oil on K and N air filters are used.. i don't know if your model is effected or not.. yet.. ((( or it that 0.06 grams at idle..)))

wayne petty · August 05, 2011, 10:09:31 PM

you will want to print this chart... read it one line at a time...

use the scan tool to read the sensor values.. and write them on the printed copy of the chart so you can see if they are within spec..

if you don't have a scan tool that will work on this...

you will want to read a post over at corvette fever...

http://forums.corvettefever.com/70/8585187/c4-corvettes/which-used-scan-tools-for-82-to-94-corvettes-with/index.html

wayne petty · August 05, 2011, 10:17:15 PM

this is the rolls royce of scan tools..

http://lincoln.craigslist.org/tls/2487378584.html

here is another..

http://omaha.craigslist.org/tls/2506761531.html

but they are both expensive.. but both probably worth the money..

it all depends on your pocket.. and how often you are going to work on pre obd2 cars... both will do OBD 2 cars... and more stuff than you could ever imagine... they are both PROFESSIONAL MODELS.. not little whimpee consumer models..

the first one was about 1500 to 2500 new..

the second probably in the 2500 to 3500 ...new..

both could be well over 5 grand with all the cables and cartridges..

warning.. individual parts and cartridges for these can be REALLY EXPENSIVE if it does not come with everything you need..

wayne petty · August 06, 2011, 12:09:04 AM

component locator for the emission and fuel injection system..

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/06/7e/8b/large/0900c15280067e8b.gif

the what is that called and where it is chart...

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Throttle position sensor.. for the 3.4

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/06/7e/3a/medium/0900c15280067e3a.gif

OPERATION

The Throttle Position Sensor (TPS) is connected to the throttle shaft on the throttle body. It is a potentiometer with one end connected to 5 volts from the ECM and the other to ground.

A third wire is connected to the ECM to measure the voltage from the TPS. As the throttle valve angle is changed (accelerator pedal moved), the output of the TPS also changes. At a closed throttle position, the output of the TPS is low (approximately 0.5 volts). As the throttle valve opens, the output increases so that, at wide-open throttle, the output voltage should be approximately 4.5 volts.

By monitoring the output voltage from the TPS, the ECM can determine fuel delivery based on throttle valve angle (driver demand).

testing the TPS

For all engines except the 3.8L, backprobe with a high impedance voltmeter at TPS terminals A and B .

For the 3.8L engine, backprobe with a high impedance voltmeter at TPS terminals A and C .

With the key ON and engine OFF, the voltmeter reading should be approximately 5.0 volts.

If the voltage is not as specified, either the wiring to the TPS or the ECM may be faulty. Correct any wiring or ECM faults before continuing test.

Backprobe with a high impedance voltmeter at terminals C and B .
With the key ON and engine off and the throttle closed, the TPS voltage should be approximately 0.5-1.2 volts.

Verify that the TPS voltage increases or decreases smoothly as the throttle is opened or closed. Make sure to open and close the throttle very slowly in order to detect any abnormalities in the TPS voltage reading.
If the sensor voltage is not as specified, replace the sensor.

REMOVAL & INSTALLATION

See Figure 6

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/06/7e/3c/medium/0900c15280067e3c.gif

Fig. Fig. 6: Throttle Position Sensor (TPS) mounting

Disconnect the negative battery cable.
If necessary, remove the air cleaner assembly along with the necessary duct work.

Unfasten the TPS attaching screws. If the TPS is riveted to the throttle body, it will be necessary to drill out the rivets.

Remove the TPS from the throttle body assembly. If equipped, inspect the TPS O-ring and replace if necessary.

WARNING
The throttle position sensor is an electrical component and should not be immersed in any type of liquid solvent or cleaner, as damage may result.

To install:
With the throttle valve closed, install the TPS onto the throttle shaft. Rotate the TPS counterclockwise to align the mounting holes. Install the retaining screws or rivets. Tighten the retaining screws to 18 inch lbs. (2.0 Nm).
Install the air cleaner assembly and connect the negative battery cable.

~~~~~~~~~~~~~~~~~~~~~~~~

idle air control valve

OPERATION

Engine idle speeds are controlled by the ECM through the IAC valve mounted on the throttle body. The ECM sends voltage pulses to the IAC motor windings causing the IAC motor shaft and pintle to move in or out a given distance (number of steps) for each pulse (called counts). The movement of the pintle controls the airflow around the throttle plate, which in turn, controls engine idle speed. IAC valve pintle position counts can be observed using a scan tool. Zero (0) counts correspond to a fully closed passage, while 140 counts or more correspond to full flow.

Idle speed can be categorized in 2 ways: actual (controlled) idle speed and minimum idle speed. Controlled idle speed is obtained by the ECM positioning the IAC valve pintle. Resulting idle speed is determined by total air flow (IAC passage + PCV + throttle valve + calibrated vacuum leaks). Controlled idle speed is specified at normal operating conditions, which consists of engine coolant at normal operating temperature, air conditioning compressor OFF, manual transmission in Neutral or automatic transmission in D .

Minimum idle air speed is set at the factory with a stop screw. This setting allows enough air flow by the throttle valves to cause the IAC valve pintle to be positioned a calibrated number of steps (counts) from the seat during normal controlled idle operation.

The idle speed is controlled by the ECM through the IAC valve. No adjustment is required during routine maintenance. Tampering with the minimum idle speed adjustment is highly discouraged and may result inPremature failure of the IAC valve.

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/06/7e/05/medium/0900c15280067e05.gif

TESTING

Disengage the IAC electrical connector.

Using an ohmmeter, measure the resistance between IAC terminals A and B . Next measure the resistance between terminals C and D .

Verify that the resistance between both sets of IAC terminals is 40-80 ohms. If the resistance is not as specified, the IAC may be faulty.

Measure the resistance between IAC terminals B and C . Next measure the resistance between terminals A and D .

Verify that the resistance between both sets of IAC terminals is infinite. If the resistance is not infinite, the IAC may be faulty.
Also, with a small mirror, inspect IAC air inlet passage and pintle for debris. Clean as necessary, as this can cause IAC malfunction.

Disconnect the negative battery cable.
If necessary for access, remove the air cleaner.
Detach the electrical connector from the idle air control valve assembly.
Unfasten the retaining screws, then remove the IAC valve assembly from the throttle body. Clean the IAC valve O-ring sealing surface, pintle valve seat and air passage.

WARNING
If the IAC pintle has been in service, DO NOT push or pull in the valve pintle. The force required to move the pintle may damage the the threads on the worm drive. Do not soak the valve in any liquid cleaner or solvent, as damage may result.

Use a suitable carburetor cleaner (be sure it is safe to use on systems equipped with a oxygen sensor) and a parts cleaning brush to remove the carbon deposits. Do not use a cleaner that contains methyl ethyl ketone. It is an extremely strong solvent and not necessary for this type of deposits. Shiny spots on the pintle or on the seat are normal and do not indicate a misalignment or a bent pintle shaft. If the air passage has heavy deposits, remove the throttle body for a complete cleaning.

To install:
If you're installing a new IAC valve, you must replace if with an identical part. IAC valve pintle shape and diameter are designed for the specific application.

If you are installing a new IAC valve, measure the distance from the motor housing to end of the cone. If it is greater that 1 / 8 in. (28mm), use finger pressure to slowly retract the pintle. The force required to retract the pintle of a NEW valve will not cause damage to the valve.

The IAC valve pintle may also be retracted by using IAC/ISC MOtor Tester J-37027/BT-8256K. Do not soak the IAC valve in any liquid cleaner or solvent as damage may result.

Install the new idle air control valve and tighten the retaining screws to 27 inch lbs. (3 Nm).
Attach the IAC valve electrical connections.
If removed, install the air cleaner assembly.
Connect the negative battery cable.
Reset the IAC valve as follows:
Turn the ignition ON (engine OFF ), for 5 seconds.
Turn the ignition OFF for 10 seconds.
Start the engine, then check for proper idle operation.

wayne petty · August 06, 2011, 12:15:52 AM

The throttle body is integral with the intake plenum on the 3.4L engine

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/06/7f/29/medium/0900c15280067f29.gif

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/06/7b/ff/large/0900c15280067bff.gif

the big list...

http://www.compnine.com/index.php?u=1&year=1993&artnbr=MW00-030&artsfx=W&supplgroup=60&catcode=15W&modelcode=W&makecode=C&modelseries=WA&uid=1&modelid=1147577251&capuid=1&majorgroup=00&grouptype=B

close up view of the TPS and IAC on the throttle body/manifold

http://www.compnine.com/index.php?u=1&year=1993&artnbr=GM03-239&artsfx=W&supplgroup=NULL&catcode=15W&modelcode=W&makecode=C&modelseries=WA&uid=1&modelid=1147577251&capuid=1&majorgroup=03&grouptype=B

Mikej · August 06, 2011, 10:21:12 AM

Fuel pump?

34ford · August 06, 2011, 12:50:46 PM

Wow Wayne,

That all makes my head spin. I probably will let my mechanic check the codes. Will check for some of the easy stuff I can do. You must be a really fast typer to post all that. Like 2000 words per minute

Mike I don't think it's the fuel pump cause you can hear it pressurize the system when you first turn on the key.

It's did this twice in the last 3 weeks.

rooster · August 07, 2011, 01:26:11 PM

Quote from: "34ford"Wow Wayne,

That all makes my head spin. I probably will let my mechanic check the codes. Will check for some of the easy stuff I can do. You must be a really fast typer to post all that. Like 2000 words per minute

Mike I don't think it's the fuel pump cause you can hear it pressurize the system when you first turn on the key.

It's did this twice in the last 3 weeks.

Put a fuel presure tester on it!

Hearing to pump come on for a few seconds , is a timed thing! It could come on for afew seconds and only pump 15 pds or 40 pds.

You can get codes read at O'Rilles auto parts for OBD1, you have to leave a deposit on the reader.

I had same symptoms as your car! It was a intermitent fuel pump fault!

34ford · August 07, 2011, 04:25:15 PM

Denny,

Does the low fuel pressure set a code???

rooster · August 07, 2011, 04:39:15 PM

Quote from: "34ford"Denny,

Does the low fuel pressure set a code???

NO! Not that I know of!

I all so got codes on mine! po341 (cam crank error) was one of them,

Something else you might try is " when the car wont start, have someone beat on the bottem of tank with a malet, while you crank engine" Thats how I found the pump probel on my truck.

Something else comes to mind is to remove fuel pressure regulater hose and smell for gas. shouldent be any!

Leon · August 07, 2011, 04:50:47 PM

I had one that didn't set any codes but would start and run for a bit then shut off. I found the ignition signal from the computer went to a transistor to feed the coil. If I hit some freeze mist on it to cool it the car would run, point the heat gun at it and it would die. replaced it (Chevy called it an ignition module) and car ran great. They had it in the shop for two weeks and because it didn't throw any codes they couldn't figure it out. I towed it back home and found it in a couple hours of troubleshooting.