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Started. Won't start. OBD1 reader won't connect.

V

vtraudt

CEG'er
Joined
Nov 17, 2009
Messages
214
We re-installed the engine, did a quick test start (without drive belt, power steering pump, etc.). Started right up and ran nice.
Installed PS pump, belt, motor mounts, etc.
Cranks, but won't start/fire.
Connected OBD1 reader: error connecting/reading.

Where to start looking? Since the reader won't connect at all, I think I should follow the ECU signal/power path?

Any suggestions?
What could
a) Prevent the engine from starting (after it started with one turn)?
b) Prevent the OBD1 reader from connecting (always did all test all the time)?
c) Where does the ECU gets its power from?
 
It has spark.
But when pushing the shrader fuel pressure valve, nothing comes out (no fuel pressure).

We checked:
- PCM memory fuse
- PCM relais
- fuel pump fuse
- fuel pump relais

We took the PCM out. Checked:
- Ground
- 12V on one of the pins (8 I think)

Can the PCM module have gone bad?
When putting the the belt and pump on, installing the battery, we had short short between the plus pole and the upper intake (brief spark). The short would have gone from +12V to Ground (through the intake), so no fuses etc. should have been in the path of the short.
 
vtraudt said:
We re-installed the engine, did a quick test start (without drive belt, power steering pump, etc.). Started right up and ran nice.
Installed PS pump, belt, motor mounts, etc.
Cranks, but won't start/fire.
Connected OBD1 reader: error connecting/reading.

Where to start looking? Since the reader won't connect at all, I think I should follow the ECU signal/power path?

Any suggestions?
What could
a) Prevent the engine from starting (after it started with one turn)?
b) Prevent the OBD1 reader from connecting (always did all test all the time)?
c) Where does the ECU gets its power from?
Click to expand...

I did it before (for other reasons) on the 2.5 Duratec: If I run the fuel pump by connecting 12V (bypassing the PCM), would the engine run (has spark and fuel)?
If so, could it be damaged?
Obviously, this does not solve the problem of the PCM not connecting to the OBD reader, but my further narrow done the error search (to PCM related issues).
 
Mega Fuse: Its tough to get to it. Before I start the process: Isn't the Mega fuse in the plastic duct on the back side of the engine only in the path from the
alternator-MegaFuse-Starter-+12V BatteryTerminal?
If so, a blown MegaFuse only prevents charging, and has nothing to do with the engine starting/running/PCM/fuel pump, right?
 
Check for the presence of your +5 Vref at the TP sensor and see if the CEL illuminates when the ignition switch is in RUN. Both are indications as to whether or not the PCM is properly powering up.
 
projectSHO89 said:
Check for the presence of your +5 Vref at the TP sensor and see if the CEL illuminates when the ignition switch is in RUN. Both are indications as to whether or not the PCM is properly powering up.
Click to expand...
With the ignition on (engine not running), there is no 5V on any of the TP connector pins.
Turning the ignition on, the CEL does NOT come on, nor stay on.

==> PCM not working properly.

What now?

How easy does a PCM module go 'bye bye'?
With the brittle/insulation cracking and falling off wires we had to deal with in the engine bay, I would more suspect that the wiggling of wires/connectors during installation of power steering pump may have created an issue.

Can an error (wires or PCM) be traced?

Other checks to perform to get to the bottom of the problem, for example bad PCM module or wiring issues?
 
Verify that the PCM power Relay energizes when the ignition switch is in RUN or START.

If the relay is energizing, check PCM connector pins 37 & 57 for battery power when relay is energized.

Also, check for proper ground on PCM pins 40 & 60.
 
projectSHO89 said:
Verify that the PCM power Relay energizes when the ignition switch is in RUN or START.

If the relay is energizing, check PCM connector pins 37 & 57 for battery power when relay is energized.

Also, check for proper ground on PCM pins 40 & 60.
Click to expand...

The PCM relay engergizes when key is turned to run.
When on, pin 37 and 57 show battery voltage.
Pin 40 and 60 have ground.

ALL other users (wiper, horn, blinker, headlights, etc.) work.
All fuses in the engine bay power box have been checked and are good.

Should I try another PCM? Does anyone here have a PCM module for a 1995 Contour GL (OBD1!) that I could use for testing?
 
Definitely try a new PCM sooner than later, I replaced all my sensors just to find out it was my PCM causing a no idle issue on my '95. I got it for $50, it would have saved me well worth that in my own time if I tried it right off the bat. My code reader would only randomly connect to the PCM, it was probably the only real direct indication it had a bad pcm.
 
As a last test, check to make certain the Vref line at the TPS is not shorted to ground. If it isn't, go for the PCM replacement.
 
1995 Contour GL 2.5 V6 auto - PCM (OBD1)

1995 Contour GL 2.5 V6 auto - PCM (OBD1)

I am troubleshooting a 'non responsive' PCM.
To find out if it is a bad module or other (wiring?) issue, I would like to install a known, good PCM.
What years/models/PCM specification will fit my car?

take it to the classifieds.


Thanks.
 
Last edited by a moderator:
again, as we have covered before, there is no need to start a new thread on the same topic.

keep the classified posts to the classifieds.

to answer the question, you need the same year and car configuration .... so you need a pcm with the same code, or a code from the same series. well the same series works for the SVT since they where all equiped the same. I would stick to the same exact code, then you know its a direct swap.
 
projectSHO89 said:
As a last test, check to make certain the Vref line at the TPS is not shorted to ground. If it isn't, go for the PCM replacement.
Click to expand...
I went to the local junkyard and picked up a PCM module from the same car.
Plugged it this afternoon: same problem. The OBD1 reader comes back with "can't read data", no CEL when turning ignition on, no fuel pump priming.
So it is not the PCM (unless the one I picked from the junk yard has the same problems).

What wire connections should I check that are the most likely to 'disable' the PCM or preventing it from (for example) turning the fuel pump on?
 
projectSHO89 said:
As a last test, check to make certain the Vref line at the TPS is not shorted to ground. If it isn't, go for the PCM replacement.
Click to expand...
Which pin/wire of the TPS is the "Vref"? Measuring from the TPS on the engine against ground, or from the connector to ground?
I assume I need to measure resistance from that pin/wire to ground (should not be a short), right?
 
At the TP connector, I measured the following, all against ground:
With ignition on:
Botton Brown/Yellow: 27.7 kOhm, 294 mV
Middle White: 0.44 MOhm, 56 mV
Top Brown/Yellow: 347 Ohm, 60 mV

With ignition off:
Botton Brown/Yellow: 0.9 Ohm, 0 mV
Middle White: 330 kOhm, 2.3 mV
Top Brown/Yellow: 0.7 Ohm, 0 mV
 
projectSHO89 said:
Please tell me you didn't try taking resistance readings with the power applied to the circuit....
Click to expand...
Yes I did. The internal resistance of modern voltmeters/multimeters is in the 250 MOhm range, the amps at 12 Volt flowing are therefore 12V/250,000,000Ohm = 0.000000048 Amp or 0.000048 mA.
 
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