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Tim's Auto Repair
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1988 chev, truck hard to start why

Customer Question

1988 chev, truck hard to start why
Submitted: 7 years ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 7 years ago.


please explain yor problem the best you can


Customer: replied 7 years ago.
I t dosent matter if the truck is cold or warm it will crank over untill you begin to think that you are going to kill the battery and then it will start. I will crank it for a while turn the key off and then crank it some more.
Expert:  Tim's Auto Repair replied 7 years ago.


does itrun good after it starts?look at the injectors obove the throttle body,let me know if you see fuel comeing out of them...also see if it will start easy with starting fluid....let me know


Customer: replied 7 years ago.

it will run good after it starts as long as the check engine light stays on or off, I have replaced the plugs the wires the cap the rotor est box with the 5 wires going into it. the ecm box and the fuel relay switch, but it seems to be flooding out and it will back fire going down the road. yes it starts good with starting fluid. and I had the timming set on it.

Customer: replied 7 years ago.
some times it cranks so long that the starter over heats
Expert:  Tim's Auto Repair replied 7 years ago.


sorry i've been offline

tell me the codes you are getting from the computer

Customer: replied 7 years ago.
Customer: replied 7 years ago.
code 13 and 42
Expert:  Tim's Auto Repair replied 7 years ago.


you may have a bad ignition module ore distibuter pic-up coil....also you have a bad conection to the o2 sensor or it is bad.....use the code charts to hpin point your problem


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DTC 13


Code 13 Open Oxygen Sensor Circuit

Code 13 Open Oxygen Sensor Circuit




4.3L "B & G" SERIES

FUEL INJECTION (TBI) Circuit DescriptionThe ECMsupplies a voltage of about .45 volts between terminals "D7" and "D6". (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volts).
The O(2) sensor varies the voltage within about 1 volt, if the exhaust is rich, down through about .10 volt, if exhaust is lean.
The sensor is like an open circuit and produces no voltage, when it is below 360 degrees C (600 degrees F). An open sensor circuit, or cold sensor, causes "Open Loop" operation.

TEST DESCRIPTION Numbers below refer to circled numbers on Diagnostic Charts.


  1. Code 13 WILL SET:

Engine at normal operating temperature.
At least 2 minutes engine run time after start.
O(2) signal voltage steady between .35 and .55 volts.
Throttle angle above 5% (approx .3 volts above closed throttle voltage).RPM above 1600.
All conditions must be met for about 60 seconds.
If the conditions for a Code 13 exist, the system will not go "Closed Loop"

  1. This test determines if the O(2) sensor is the problem, or, if the ECM and wiring are at fault.
  2. In doing this test, use only a high impedance digital volt ohm meter. This test checks the continuity of CKTs 412 and 413. If CKT 413 is open, the ECM voltage on CKT 412 will be over .6 volts (600 mv).

Diagnostic Aids: Normal "Scan" voltage varies between 100 mv to 999 mv (.1 and 1.0 volt), while in "Closed Loop". Code 13 sets in one minute, if voltage remains between .35 and .55 volts, but the system will go "Open Loop" in about 15 seconds.
Verify a clean, tight ground connection for CKT 413. Open CKT(s), 412 or 413 will result in a Code 13. If Code 13 is intermittent,

DTC 42


Fig. 040 - Wiring Diagram for Code 42 Electronic Spark Timing. VIN Z





Circuit Description: When the system is running on the Ignition Module, that is, no voltage onthe bypass line, the Ignition Module grounds the EST signal. The ECM expects to see no voltage on the EST Line during this condition. If it sees a voltage, it sets Code 42 and will not go into the EST mode.
When the rpm for EST is reached (about 400 rpm), and by-pass voltage applied, the EST should no longer be grounded in the ignition module so the EST voltage should be varying.
If the by-pass line is open or grounded, the ignition module will not switch to EST mode so the EST voltage will be low and Code 42 will be set.
If the EST line is grounded, the ignition module will switch to EST, but because the line is grounded there will be no EST signal. A Code 42 will be set.

Fig. 039 Chart - Code 42 Electronic Spark Timing

Test Description: Numbers below refer to circled numbers on the diagnostic chart.


  1. Code 42 means the ECM has seen an open or short to ground in the EST or bypass circuits. This test confirms Code 42 and that the fault causing the code is present.
  2. Checks for a normal EST ground path through the ignition module. An EST CKT 423 shorted to ground will also read less than 500 ohms; however, this will be checked later.
  3. As the test light voltage touches CKT 424, the module should switch causing the ohmmeter to "overrange" if the meter is in the 1000-2000 ohms position. Selecting the 10-20,000 ohms position will indicate above 5000 ohms. The important thing is that the module "switched".
  4. The module did not switch and this step checks for
    1. EST CKT 423 shorted to ground.
    2. Bypass CKT 424 open.
    3. Faulty ignition module connection or module
  1. Confirms that Code 42 is a faulty ECM and not an intermittent in CKT's 423 or 424. Diagnostic Aids: If a Code 42 was stored and the customer complains of a "Hard Start", the problem is most likely a grounded EST line (CKT 423).

The "Scan" tool does not have any ability to help diagnose a Code 42 problem.
A PROM not fully seated in the ECM can result in a Code 42.

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