89 Escort LX 1.9L CFI -- Fuel delivery is out of wack

To add to my last post, I just checked all the wiring from the distributor to the computer and all four wires check good for continuity. I am getting spark at the coil so I will assume for now that I am getting pickup signal to the computer.

One wire has an 'ignition suppressor resistor' in series between the distributor and the computer and it reads 22,000 ohms.

So now I want to check the TPS.

Mike, if you know of any other conditions outside of a faulty computer that might result in no grounding of the fuel injector when the engine is cranked, please, by all means post them.

Here's what I know with a very high degree of certainty.

1. The injector works.

1. The fuel pump and pressure regulator are working.

2. There is no voltage to the injector at startup.

1. The injector wiring is sound.

2. The distributor wiring to the computer is sound and I am getting spark at the coil.

1. The wiring from the TPS and the MAP sensor to the computer is intact.

2. Disconnecting the TPS and MAP sensors does not enable the injector. I may be wrong, but with my limited knowledge I can only conclude from this that the TPS and MAP sensors do not play a part in the failure of the computer to ground the injector circuit.

I am looking at a *complete* failure of the grounding of the injector at startup. Nada, zero, zilch. I have managed, to my satisfaction, to eliminate all known (to me) possibilities that might cause this problem with the exception of the computer.

If the computer is good,

If there is proper fuel pressure to the injector,

If the injector and its circuitry are good,

If the coil is firing and the wiring from the distributor to the computer is intact,

If the MAP, TP, ECT, ACT and O2 sensors are disconnected,

Then the computer should be grounding the injector circuit at startup.

From everything that I know so far, the computer is faulty

OR

Something that I don't see is interfering with the computer's ability to ground the injector at startup.

I have been adding to this post all morning. See the one just previous to this one to aarcuda it has the very latest.

Only thing I can add is make sure the puter has a good solid ground. I suspect that it does otherwise you'd have more issues, but it's easy enough to check - run a test lead from the puter case to a known good ground and try again.

nate

Thanks nate, I used two different tests to confirm good ground.

I fired the injector through the computer wiring harness while it was unhooked from the puter. I shorted the injector signal wire directly to the ground wire in the puter harness and turn the key on. The injector fired.

Then I ran aarcuda's test of backprobing the ground wire with the positive lead of a digital volt meter while connected the negative lead to battery ground while the harness was connected to the puter and then running the KOEO test to check for any voltage drop. There was none.

Now I'm waiting for the battery to recharge enough to continue.

And thanks to all for the help...

Components that I know or feel strongly are good... and why

1. *Fuel Pump and Fuel Pressure Regulator* Both work to keep fuel pressure within specs, 13 to 17 psi, after brief cranking for the alloted time of 60 seconds.

1. *Fuel Injector* The fuel injector will spray fuel continuously when hooked up to the battery, and fuel pressure is maintained.

2. *Fuel Injector Wiring* Fuel injector works as described above when the current is routed through the fuel injector wiring that is used by the computer. With the wiring harness disconnected from the computer and the injector signal wire shorted to the ground wire at the plug and using the red +12 volt wire to the injector, when the key is turn on, the injector fires.

1. *Wiring from the Distributor to the Computer* These wires were tested for continuity with a a digital ohm meter and found to be intact. The coil is firing a strong spark when the engine is cranked.

2. *Computer Ground Circuit* This circuit was tested by backprobing the ground wire at the computer with the positive lead of a digital volt meter and attaching the negative lead to battery ground and running the KOEO test. There was no voltage drop. The procedure in #3 confirms that the computer grounding circuit is good.

1. *Throttle Position Sensor* I checked the TPS as per the Chilton manual with the following results: VREF = 5 volts Voltage range was from .76 volts at fully closed to almost 5 volts at full opened, measuring across the appropriate terminals. The TPS wiring to the computer is intact as measured by a digital ohm meter.

2. *EGR Valve* I removed and inspected the EGR valve. It moves freely when 5 to 10 pounds of vacuum is applied. All vacuum lines are intact. I did *not* yet check the valve that opens the vacuum line to the EGR valve as the engine warms up.

1. *MAP Sensor Wiring* The MAP sensor wiring to the computer is intact as measured by a digital ohm meter. I have yet to test the MAP sensor itself.

Today, at different times, the injector both fired and did not fire when cranking the engine. At one point I used a #194 bulb to check the injector harness and the bulb pulsed as the engine was cranked. At another time the injector was hooked up as I cranked the engine and the engine started, albeit with a heavily rich mixture. But mostly the injector would not fire when the engine was cranked. After going through all this, I pulled codes and found that the computer set Code 95 again, 'Fuel pump secondary circuit failure', although the fuel pump worked flawlessly when grounded through the FP test terminal at the test socket, and when turning the key on and turning it off, the latter only if pressure below a certain level.

Things I should check:

MAP sensor values Coolant temp sensor values Fuel pump relay

At this point, even though they rarely fail, I am becoming very suspicious of the computer. But before I take that step I want to exhaust all other possible causes so please feel free to add to the list.

I notice on the wiring diagram for the computer that an 'EGR vacuum regulator' is hooked up to the computer. It appears to be an electromagnetic solenoid, but it's function is unclear. Just looked it up. It is analogous to the EGR port on a carb. Basically tells the EGR valve when to open. Appropriately named.

I don't know how this computer is programmed to control gas flow through the injector and how any given failure in any given sensor or component might cause the computer to shut down gas flow by ceasing to ground the injector. aarcuda explained how malfunction of the TPS could cause the computer to issue a 'clear flood' command at idle which would shut down the injector, but the TPS sensor and its circuitry tests out okay.

Make sure the ecm is getting a pip signal.

Steve,

I checked all the wires going from the distributor to the ECM They are all intact and the coil is producing spark. I guess I should check all the wires to make sure that none are grounded or shorted to any other wires in the computer harness. If the wiring is in good shape and I am getting spark, it seems like there's a pretty good chance I am getting PIP signal to the computer.

How much more sure can I get with a digital automotive meter with dwell and duty cycle functions? I also have an analog meter. I would think that I should see some indication of a signal if I hooked up the analog meter to read volts across the signal wire and ground.

There are four wires going from the ignition module at the distributor to the computer. One is going through what the wiring diagram in the Chilton manual refers to as a "shorting plug".

Another wire goes from the ignition module through a 22,000 ohm "ignition suppressor resistor" to the computer. This wire also connects the ignition module directly to the coil. The other two wires are direct connections from the ignition module to the computer.

I don't know which of these wires carries the PIP signal, so I will check them all for any sign of life while cranking the engine.

1. *Ignition system* The ICM is new and the ignition system produces spark under all conditions that I have described so far. All I know for sure at this point about the wiring from the ICM to the computer is that it is not open.

Steve,

Confirmed getting PIP signal to PCM.

I was able to identify the PIP signal wire coming out of the ICM wiring harness following the link below. It's a link to a .doc file which asks whether you want to open it or save it to disk. I had to download Word Viewer 2003 from Microsoft but it was exactly what I was looking for. It pinpointed the location of the PIP signal wire coming out of the ICM module going to the computer. I disconnected the coil wire and backprobed that wire at the PCM harness. I used an analog meter set to

25 volts DC and measured across the PIP signal wire and ground while cranking. The needle on the meter went up to 5 volts and pulsed there as the engine cranked.

megasquirt.sourceforge.net/extra/doc/ford-Ignition-tfi-edit.doc

1. *PIP Signal to PCM Confirmed* I disconnected the coil wire and backprobed the PIP signal wire at the PCM harness. I used an analog meter set to 25 volts DC and measured across the PIP signal wire and ground while cranking. The needle on the meter went up to 5 volts and pulsed there as the engine cranked.

(This is all being done to diagnose why the PCM is apparently not grounding the injector signal wire at startup.)>

I just checked the MAP sensor and got the following results:

VREF is 5 volts

Signal voltage as measured across the SIG RTN and MAP/BARO SIG (designations from Chilton manual) *is stuck at 2.5 volts*, from atmosphere all the way up to 20 inches of vacuum.

So now the question is, which of the symptoms this car exhibits is could be caused by this condition.

The two symptoms are:

1. Sometimes (most times, lately) the injector does not fire at startup.

1. When the injector does fire at startup and the engine starts, the fuel mixture is exceedingly rich at idle.

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The reason why I put off testing the MAP sensor is because of the perceived difficulty (at the time) of accessing the wires with the harness connected. The wires to the plug exit from the bottom and it is very difficult to access the backprobe needles with alligator clips.

I solved this by soldering three 12" pieces of small gauge insulated wire to three sewing needles. The wires came from a defunct computer power supply and I was able to use different colors.

I would not condemn the MAP sensor yet. The readings you got are typical. The MAP sensor sends a variable frequency to the ECM - not variable voltage. The symptoms you describe sound more like a bad ECT sensor. The ECT has a variable resistance depending on engine temperature. IIRC, it is mounted on the intake manifold on that one. I hope I am remembering the right one!! It has been a long while since under the hood of an Escort.

Lugnut

As soon as I eat something I will test the ECT.

I can't imagine that it would be the reason for the injector not firing while the engine is cranking at startup though.

What you wrote concerning variable frequency jibes with what I have just read elsewhere. The info in the Chilton manual seems to be wrong, then.

The manual says to access the appropriate terminals with a DVOM and with the sensor connected to the harness and a vacuum pump attached, turn the key to on and apply vacuum.

"If the DVOM voltage varies with the varying vacuum, the sensor is functioning properly."

I just checked the ECT. It checks fine for cold. No way at present to check it hot without yanking it and putting it in boiling water, but if it checks out okay cold, then it is not the problem.

1. *MAP Sensor* Map sensor replaced with new one.

1. *ECT Sensor* ECT sensor checks out okay for resistance and voltage while cold. Since the problem is with starting, no reason to check it for warm at this point.

This is getting down to any wiring that I haven't checked yet and the engine control computer. Everything else of any consequence checks out okay.

The computer only fired the noid light once in the 3 or 4 times that I used it. This behavior is consistent with the behavior of the injector lately.

The fuel pressure is right on specs. I check the fuel pump only and it was 14.5 psi. System pressure with the the fuel pressure regulator involved was 14 psi.

I have checked every component that could possibly be involved in this behavior except the engine computer and some of the wiring associated with it.

Everything that I tested so far is included in the post:

"Re: 89 Escort LX 1.9L CFI -- WHAT I KNOW SO FAR"

posted at 4:10 PM today

Does the computer always fire your noid light? If it fires your noid light but not the injector, you may have too much fuel pressure.

A large part of diagnosis is determining what is working correctly.

Newer entries at the bottom

Components that I know or feel strongly are good... and why

1. *Fuel Pump and Fuel Pressure Regulator* Both work to keep fuel pressure within specs, 13 to 17 psi, after brief cranking for the alloted time of 60 seconds.
2. *Fuel Injector* The fuel injector will spray fuel continuously when hooked up to the battery, and fuel pressure is maintained.
3. *Fuel Injector Wiring* Fuel injector works as described above when the current is routed through the fuel injector wiring that is used by the computer. With the wiring harness disconnected from the computer and the injector signal wire shorted to the ground wire at the plug and using the red +12 volt wire to the injector, when the key is turn on, the injector fires.
4. *Wiring from the Distributor to the Computer* These wires were tested for continuity with a a digital ohm meter and found to be intact. The coil is firing a strong spark when the engine is cranked.
5. *Computer Ground Circuit* This circuit was tested by backprobing the ground wire at the computer with the positive lead of a digital volt meter and attaching the negative lead to battery ground and running the KOEO test. There was no voltage drop. The procedure in #3 confirms that the computer grounding circuit is good.
6. *Throttle Position Sensor* I checked the TPS as per the Chilton manual with the following results: VREF = 5 volts Voltage range was from .76 volts at fully closed to almost 5 volts at full opened, measuring across the appropriate terminals. The TPS wiring to the computer is intact as measured by a digital ohm meter.
7. *EGR Valve* I removed and inspected the EGR valve. It moves freely when 5 to 10 pounds of vacuum is applied. All vacuum lines are intact. I did *not* yet check the valve that opens the vacuum line to the EGR valve as the engine warms up.
8. *MAP Sensor Wiring* The MAP sensor wiring to the computer is intact as measured by a digital ohm meter. I have yet to test the MAP sensor itself.

1. *Ignition system* The ICM is new and the ignition system produces spark under all conditions that I have described so far. All I know for sure at this point about the wiring from the ICM to the computer is that it is not open.

2. *PIP Signal to PCM Confirmed* I disconnected the coil wire and backprobed the PIP signal wire at the PCM harness. I used an analog meter set to 25 volts DC and measured across the PIP signal wire and ground while cranking. The needle on the meter went up to 5 volts and pulsed there as the engine cranked.

1. *MAP Sensor* Map sensor replaced with new one.

2. *ECT Sensor* ECT sensor checks out okay for resistance and voltage while cold. Since the problem is with starting, no reason to check it for warm at this point.

1. *PCM Wiring Harness* I unplugged as much as I could and checked each and every wire going to the engine computer for being shorted to ground and for being crossed with every other wire. Results were negative.

So now I am down to:

The PCM, the Powertrain Control Module The ECC, the Engine Control Computer The ECU, the Engine Control Unit The EEC, the Electronic Engine Control

or, as it is commonly referred to...

The *Brain Box*

I'm with you on that. To paraphrase:

When you eliminate everything that is working, whatever is left must be broken.

The ECT, as I posted elsewhere, is measuring good while engine is cold. I just came in from testing the PCM wiring harness. I disconnected everything I could get my hands on and tested each wire at the PCM plug (unplugged) to see if it was shorted to ground or crossed with another wire. I thought I found something when I came across an orange wire that was shorted to ground. I came inside to look at the manual, but the orange wire is a ground wire.

Everything came up negative for short to ground and crossed with another wire.

At this point I'm looking at a failed computer.