2.9 v6 problems continue

Tedybear · Jul 18, 2014

Okay. This is getting rather annoying. As much as I like driving the wife's Beetle? I need to get this Bronco II back in good shape.

Intake leak cured. Small amounts of white smoke when the truck starts up after not being run for a few days. Figure it's the usual condensation burning off.

Issues: Starts HARD! Spins rather quick and seems to want to 'catch'. After several tries it finally starts--and then stalls out like the idle dropped to zero.

Does this a few times and finally will start and run. Here's the rub: The RPM on a stone cold start---about 750-800 RPM. It's acting like the computer is commanding the system to enter "closed" loop upon start up and not giving the engine a chance to warm up.

The fuel pressure and such as been tested over and over and over. It's fine. Spark seems to be strong. (jumps a very large arc when tested)

The fun part? After the engine finally warms up? Runs pretty good! I ran it on a 30 mile round trip and worked the day lights out of it. Goosed it several times, 0-60 heavy throttle. Once it's there, it's great.

This truck has always had an issue with cold starts. Leave it alone for a day or two and it used to start---stall---start and continue running. Seems what ever is causing that issue? Has worsened.

I'm planning on doing a full tune up on it in the near future. I've inspected the plugs, wires are in fair shape, cap and rotor pulled and inspected. Fairly good shape.

It's just like the truck 'thinks' it's already warmed up and in closed loop.

Does anyone think the coolant temp sensor for the computer may have tossed it? If it's reporting the engine is at temp, or 'hot'...even when stone cold? Could it be commanding the system to run "leaner" and at the lower RPM?

Looking for some direction on this one. Due to being almost out of $$ for these projects (and needing to do the service on the wife's car...oil change and manual trans fluid change..that's not cheap for all the syn. fluid it calls for)

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ab_slack · Jul 18, 2014

It's just like the truck 'thinks' it's already warmed up and in closed loop.

Does anyone think the coolant temp sensor for the computer may have tossed it? If it's reporting the engine is at temp, or 'hot'...even when stone cold? Could it be commanding the system to run "leaner" and at the lower RPM?

Well, yeah, of course.

If it is "just like the truck 'thinks' it's already warmed up and in closed loop" then check out the engine coolant temperature sensor.

I recently did a diag on mine. Other than being a PITA to get at the contacts when unplugged, it is a simple measurement.

http://www.therangerstation.com/forums/showthread.php?t=151049

Tedybear · Jul 18, 2014

Interesting information. I'm wondering if a way to test this theory would be to unplug the sensor..It would then have max resistance. (Now that'd be a coldddddd engine) and seeing if the engine starts normally.

Or just saying screw it and hooking up a resistor into the socket. Nice thing about my job is I have access to resistors for the electronic repairs. Just throw in a resistor rated at about 47k-50k..And see if the engine fires up like it should. Have to shut it down afterwards, can't unplug a sensor in some cases without throwing a code or such.

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ab_slack · Jul 18, 2014

Well it occurred to me that you could fake the resistance that way and see how it does but decided not to mention figuring odds were you didn't have resistors. So, yes that be an easy test and easier to establish connection to wires than get in that socket (tho it isn't the easiest to unplug.

Only challenge I see is the resistor lead (unless high wattage) may be a bit thin to get reliable connection but then again with a leaded resistor bending the lead over may give the thickness. I can't remember if the sensor had round pins or spades. I think it was round which is why diameter may be an issue. But it is a good way to test.

Pulling out the sensor will change things for sure. If it recognizes sensor is bad it will probably go into some open loop default which will be better than thinking it is all warmed up. At least it seems logical approach.

But you know what they say about logic...it is a great way to F up with confidence.

Tedybear · Jul 19, 2014

I'd say the heck with it and just change it out. However the replacement sensor runs about $30ish or so from our local stores. That's about the cost of 1/2 of the oil change and the transmission service the wifes car is long overdue for.

It's a rough call, I've never really had the coolant sensors give out. Most 'Resistors' when they fail, will open the circuit..not short out.

It's all I can think of for this oddball issue. Considering how well the engine runs after it's warmed up..

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Tedybear · Jul 19, 2014

Minor update:

Pulled the pig tail before I went into work. The truck started right up with no issues. The idle spike high to 1500RPM..and about 3 seconds or so later? Nose Dived back to barely able to idle 700-800rpm. And of course the check engine light kicked 'on' when it figured out the sensor was unplugged.

I shut the truck down and plugged it back in. The trucks started up with low idle..and the CEL was shut off.

I'll have to dig out the meter to ohm it out, but that's kinda odd that it would spike high idle...and then go into what could only be described as a flaky limp mode...

Odd....

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RonD · Jul 19, 2014

This is a good page to bookmark for EEC-IV computers: http://www.auto-diagnostics.info/ford_eec_iv

You can test the ECT(engine coolant temp) sensor while in place.
The ECT sensor has TWO wires, it looks similar to the 1 wire sender that the dash board temp gauge uses.

With key on engine off, use a sewing pin to pierce 1 wire on the ECT sensor, with voltage meter set at 20vDC ground the black probe and put the red probe on the needle.
If it reads 4.5v to 4.9v then that is the "power" wire from the computer, pin 26 "sensor reference voltage"

Switch needle to the other wire, 68degF = 3.1V, 104degF = 2.2V, 212degF = 0.5V

You need to test BOTH wires, there could be a problem with the reference voltage, either from the computer's 5v regulator or in the wiring, if reference voltage is only 3volts at the ECT sensor then computer would think engine is warm all the time.

The 5volt reference voltage is also used on the TPS(throttle position sensor), and the IAT(intake air temp) sensor, so if ECT sensor shows less than 5v, test TPS for 5v, and IAT sensor for 5v.
Also unplug each sensor and test for 5v, it could be one of these sensors is drawing down the voltage on the other 2.

Tedybear · Jul 19, 2014

I'll give it a whack. I've watched YouTube's "Scanner Danner" enough to keep my noggin up to date (somewhat) on these issues.

I've got push pins for back probe of wires and gator clips for the meter. Be nice if all this was--just a dirty contact somewhere easy to find. LOL. (Yeah, like that's my luck)

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Tedybear · Jul 19, 2014

Interesting.

This gets better and better. I think I'll need popcorn and a soda for all this entertainment I'm getting.

4.6 volts for reference. Not uber great...but it's fair enough. Took a while to get the flippen lead into place.

While running, the reference voltage kicks down dramatically.

The return/signal voltage? Hovers around (get this....) 062.4mv If I rev the engine up? The voltage goes up slightly to 71.0mv. The engine was warming up during this. The plug is also starting to fall apart. (getting crispy) The contacts where secure for this test.

The voltage never enters signal digits. It stays in the millivolt range while warming up.

So that's where it sits. Plugged in and "Working" the feed voltage goes from 4.6 and tanks down. While that's interesting? The fact the return/signal line refuses to enter anything above the millivolt range. pretty much isn't good news. Unless I'm doing this test wrong. Black meter lead clipped to battery ground. Red lead backprobed into the end of the connector plugged into the sensor.

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RonD · Jul 19, 2014

Reads like the resistor in the ECT sensor is open, broken, if I am read what you wrote correctly
62.4mV = .0624volts

You can test OHMs between the two ECT pins to confirm, it should read N/C(no connection) or super high number, infinite, if ECT is bad

The mv change with RPM is just the alternator, the return wire to PCM will have mv reading because it is a circuit inside the PCM, so there is no voltage passing thru the ECT sensor IMO.

Tedybear · Jul 19, 2014

That's about how I read it. I'll go ahead and read across the harness. Nice thing about this truck-- The main harness connections are in good shape. So if I unplug all 3 "Trunk lines" it will leave one half of the circuit "open" so I can do the test without pulling it apart.

It makes sense, if the coolant temp sensor is telling the computer the engine is well over 100c....Yeah, that would create some havoc with the air fuel mixture when it's stone cold.

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Tedybear · Jul 19, 2014

Question that has been bothering me.

The CEL did come on and the computer commanded the truck to hit 1500 RPM when I first disconnected the sensor and then started the truck.

If the sensor was "Open Circuit"---shouldn't that also trigger the CEL?

Just a bit confused.

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RonD · Jul 19, 2014

If CEL came on when you disconnected ECT then yes you would expect your readings to also trigger the CEL.

Tedybear · Jul 20, 2014

This just gets funner and funner.

Okay....

Did a backprobe at the connections at the "Trunk" (aka, main harness) Took a bit to figure out which wires went to what....

The line with the 4.66 volts.

And the other line with the MV settings....

The line with the 4.66 volts? That's the line changing state when the engine runs. The voltage slowly and in a very steady fashion slowly dropped to less then a volt with the engine warming up.

The other line with the MV? (the milli volt range) Didn't change or move around at all. Fairly steady.

Now I do not pretend to know everything about electronics....But shouldn't the supply voltage remain at 4.66vdc...and the other line...shouldn't that be the one doing something? Cause it looks like I have the supply line dropping the voltage to 3.3ishvdc when I first start the truck up, and it slowly drops as things warm up. (and everything in circuit...out of circuit with the sensor unplugged? I have 4.66) The other line seems to do nothing?

This kinda blows my mind away. On the flip side? again--once the truck is warmed up---she runs fantastic....

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RonD · Jul 20, 2014

That could be correct readings on your engine and year.

The Light Green/red stripe or Light Green/yellow stripe wire would have the voltage going lower as engine(ECT) warms up, pin7

The MV wire, Black/white strip or Gray/Red stripe, can appear as a ground, pin46 Signal Ground

That is according to this diagram: http://www.therangerstation.com/tech_library/EDiagrams/files/Diagrams_ElectronciEngControls2_9_2of3.JPG

2.9 v6 problems continue

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