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

A bad ECT is usually open or shorted. IIRC a reading in the

7-10 Kohm range cold should be a working one. The FSM and some others have a temp chart for reading accuracy. It seems I had a couple of 4 bngers that had a broken (intermittent) connection inside the boot of a sensor connector that would give this behavior. Those can best be found with a wiggle test. A fellow named Probst had a book out a few year back on Ford Fuel Injection that had good info on the systems and how they worked or didn't work. In any case, the wiggle test are usually done from the connector to the ECM with a DVOM connected to each pair of feeds. You will need to ID the ECM wiring diagram to put the pairs together for a circuit. From there, you basically track the harness of each circuit flexing it and all the connections while looking for a change. There are circuit signal gens that make this easy for a fair amount of cash. Home centers like HD and Lowes sometimes have an inexpensive one.

Lugnut

Reply to
lugnut
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Ahh... the wiggle test. You could wiggle yourself into a strait-jacket with this stuff. I have nothing but goodwill for this car and I am on its side, BUT... I draw the line at wiggling. For tonight, anyway.

I got a computer coming from a junkyard in Philly. 40 bucks delivered. If that don't fix it, I'll start wiggling things.

I would love to get my hands on that Probst book. There's one up for auction on ebay:

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I bet that with that book and about $500 in tools I could set up shop. I'm thinking O-scope, signal generator and a few other goodies. I could go mobile.

Reply to
Simpson

You could add two zeros and still not be close.

Reply to
aarcuda69062

Guess I'll just have to tick with brains and paper clips

Reply to
Simpson

Today I checked all but two wires in the computer wiring harness for continuity between the computer and the the component it is connected to. All the wires I checked are good. The only two that I could not check without going totally bonkers were a wire to the fuel pump and one to some part of the air conditioning system. I am not concerned about the wire to the fuel pump because I think it only senses a condition and it doesn't play an active role in operating the FP. The wire to the FP relay checks out okay.

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

Newer entries are at the bottom.

  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.

  2. *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.

  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.

  2. *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.

  2. *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.

I check every wire in the PCM wiring harness for continuity from the computer to its final destination. All wires are good.

Reply to
Simpson

After I checked all the computer wires for continuity I put the freshly charged battery back in and did a KOEO test.

I got Code 22 -- 'MAP sensor input out of test range.'

This is with the old MAP sensor installed. For those who have not been following this story with bated breath, I did the Chilton manual test of the MAP sensor yesterday. The voltage across two terminals was suppose to change from zero volts at atmosphere to Vref of 5 volts at 20 pounds or so of vacuum. Well the old MAP sensor showed 2.5 volts at atmosphere and didn't budge at 20 pounds of vacuum, so I ran out and bought a new one.

I brought it back and stuck it in and tested it the same way and damn if the damn thing didn't read that same damn 2.5 volts at atmosphere and the same damn 2.5 volts at 20 pounds of vacuum and I felt like I just threw 70 bucks down the crapper. I pulled it off the car without trying to start the car with it and put it back in the box and figured I could try to sell it on ebay if Kragens wouldn't take it back.

So today, after checking all the wires and installing the battery and running the KOEO test and getting Code 22 -- 'MAP sensor input out of test range', I put the new MAP in and the computer liked it and gave it a big thumbs up and then I thought, "Oh, god... maybe it'll start!"

And it did, just like that. I checked the spray at the injector and it was fine and delicate like it should be at idle. The engine ran for 10 to 15 seconds and I shut it off, wanting to savor the moment and not wanting to push my luck.

The test procedure in Chilton's must be pretty much the same as in the Ford manual. lugnut hipped me to the fact that frequency plays a part in there somewhere. Whatever the proper procedure is for testing the MAP sensor, I may never know, but someone screwed up when the Chilton manual was written. Whether it's the same in FSM, I don't know.

But anyway, there it is. Now I have to clean up and test drive it and see if all the problems were caused by this one MAP sensor.

Reply to
Simpson

Did you buy the MAp before or after Lugnut explained that the Chilton book was dead wrong ?

Bad info yields bad results.

Actually, the Ford manual procedures are nothing like the (seemingly endless) erroneous test info given by Chiltons.

Is there no local library where you might reference and/or check out serious repair information?

Here's what you saw; the MAP sensor is fed a 5 volt reference voltage by the ECM, the output signal of the MAP sensor is a varying frequency of that 5 volt reference at 50% duty cycle. (Viewed on an O-scope, it is a square wave.) Your DVOM showed the 50% duty cycle of the 5 volt signal as 2.5 volts. Had you had a meter that is capable of measuring frequency, you could have merely switched to that function and read the KOEO and KOER frequency output and compared them to spec. (or simulated with your vacuum pump)

See my last paragraph. (when I sold O-scopes for a living, I used a Ford MAP sensor powered by a 9 volt battery during trade shows to demo the labscope functions of our product)

Yes they did. Not even good for a wheel chock. You screwed up when you didn't follow what Lugnut explained about the MAP sensor's output signal.

Even though the car may now be fixed, it is important that you understand all of the distinctions involved because frequency output devices are much more prevalent on newer vehicles.

I assure you, it is NOT.

Fingers crossed...

Reply to
aarcuda69062

lugnut offered knowledge about the role of frequency in the operation of the MAP sensor. He didn't "explained that the Chilton book was dead wrong".

But to satisfy your thirst for knowledge, I bought it as soon as I ran the questionable Chilton tests and before I read lugnut's post.

There's an old saying where I come from:

"Dumb luck and dogged determination beat a full house every time".

Easy to say when you have umpteen thousand dollars worth of test equipment and your talking to a man who relies on a cheap DVOM and paper clips... and gets results.

Okay...

I did what i could with what i had. The library was closed that day.

Thanks... one day, I'll have to look that up.

Like I said, one day, I'll have to look that up.

You seem bound and determined to come off as an asshole.

Quote what lugnut said to back up that last comment or dry up and blow off.

Well thanks...

Reply to
Simpson

There's an old saying where I come from:

Test don't guess.

Not easy to say and it doesn't have anything to do with how much I have invested in equipment. Thirty two bucks at Sears will get you a meter that will measure frequency (and AC-DC volts, resistance, current, duty cycle, etc.)

Tell ya what Homer, when it's time for that quad bypass surgery, don't be a bit concerned if the surgeon comes at you with a butter knife, a little "dumb luck and dogged determination" is all he needs.

"That day?" You've been at this for more than one day.

The starting point to any auto repair. Or do carpenters not bother to look at the blueprints until after the house is built?

Here ya go; In article , lugnut wrote: " 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. "

Even though you have no less then nine threads started on this one shitbox car, there it is.

Okay, you win. I'll blow off. Good luck with your auto repair ventures. A number of posts back, you wished for electric cars. It left the impression that you understood a few basics. My mistake.

Reply to
aarcuda69062

aarcuda69062 wrote in news: snipped-for-privacy@news.chi.sbcglobal.net:

I've been following this thread with interest, my own electrical understanding being less than great.

Honda also uses MAP sensors in most of its cars. I have several Honda factory repair manuals. In all of them, MAP sensor troubleshooting is officially done using voltages, not frequency.

Why would this be?

Reply to
Tegger

Why does one company favor voltage and another favor frequency? Design choice.

I think the advantage to using frequency is that it gives greater scaling.

Why does the troubleshooting specify voltage instead of frequency? Because that is the correct measurement unit.

Reply to
aarcuda69062

Different type of sensor

Reply to
Steve Austin

aarcuda69062 wrote in news:nonelson- snipped-for-privacy@news.chi.sbcglobal.net:

Combining yours and Steve Austin's posts, this is what I'm comprehending:

All MAP sensors do not require to be diagnosed using the same unit of measurement.

If it says in the factory FSM that a particular MAP sensor should be tested using voltage, then that's the correct unit to use for /this/ specific MAP sensor. If the FSM says to use frequency instead, then that's the correct unit for /that/ specific MAP sensor.

Reply to
Tegger

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