Ford 5.0 EFI problem and a question

[32 Chevy]

My wife and I just returned to the Northwest after a 6,234 mile jaunt from the Seattle area to chicago, down a route 66 to Albuquerque NM and then north through he national parks in Utah, Colorado at al. We drove our 56 ford 2 door Ranchwagon powered by a 1991 5.0 HO mustang motor with AOD.

It was a great time - basically the car ran great (22.5 mpg overall average) and it was lots of fun talking to folks from all over the world who admired the car. There were a couple of routine repairs - wheel bearing and pinion seal - but not really unexpected because those parts were originally boneyard stuff anyway.

But there is an unresolved issue with the fuel injection. It's going to be hard to find because it is sporadic and ONLY occurs when the ambient temperature gets into the 80's while doing stop and go driving ... Idling at a light, light throttle, idling at the next light.... Then it suddenly runs rough, stumbles, dies. Then after it sits for 5 to 15 minutes it starts right up and runs fine again. Frustrating, especially during the Springfield parade to the show! If this was a carbureted car I'd suspect vapor lock but EFI isnt susceptible to vapor lock, right?

I checked the codes - 51, 67, 81, 82, 84, 95, 29 came up. Of those the one that caught my eye was 51; ECT sensor out of range. So I changed the sensor but no difference. I had also heard that the module on the distributor can cause hesitation / stalling when warm so I also changed that with no difference.

Codes relating to pollution may not be pertinent because I don't have an air pump nor cats on it. Code 95 - fuel pump secondary circuit fault may or may not be pertinent because I'm running an external pump. Code 84 - vacuum circuit failure - hmm.

Searching the mustang boards it appears this isn't a rare problem with OBD1 fords but solutions are equally rare. So, I'm coming to the RRT community hat in hand hoping someone can shed light where to look. Thanks!

[kb426]

What are you using for a wiring harness? Did you eliminate the egr circuit? One of the codes is about vss. Are you using the vss? How many grounds do you have and where are they connected? Is this the first long trip where the car was at full operating temp for a couple of hours? Do you have an inline or intank fuel pump? Is the tank vented well? How does it idle before it's hot? That's plenty of questions to get started.

[32 Chevy]

What are you using for a wiring harness? Did you eliminate the egr circuit? One of the codes is about vss. Are you using the vss? How many grounds do you have and where are they connected? Is this the first long trip where the car was at full operating temp for a couple of hours? Do you have an inline or intank fuel pump? Is the tank vented well? How does it idle before it's hot? That's plenty of questions to get started.

Ok, here we go....

The car has been running for about 10 years. We drive a lot but mostly in our cool Northwest weather. This is the first time  in slow traffic in continued 80+ ambient temperature. The only other time there is a miss is occasionally when warming up, driving at low acceleration it may cough or backfire briefly then run great.

Wiring is an original harness. It came out of a jeep with 5.0 so I don't know if anything was changed or deleted in the egr circuit. Grounds are as provided on the wiring harness and all look solid.

No vss.

The 56 tank is real wide and flat so to prevent starvation I have a low pressure pump to a pony tank that furnishes constant flow to the high pressure pump. The pony tank is sealed - return line goes to the pony tank, not the 56 tank. The 56 tank is vented but the pony tank is sealed. (Pony tank is actually a large fuel filter housing)

[wayne petty]

first step...     print and perform this 6 part voltage drop test..

http://i.imgur.com/WMDprhm.jpg

it took me a LOT of years to assemble the six steps.. and prove it works..

please perform after the first six... a modified test 4 between  the engine and the pair of wires coming out of the wiring harness near the ecm connector..

you may also want to verify that the wiring connection at the starter solenoid is clean and tight..  wire brushing both sides of each ring terminal there then reinstalling.. them... depending on how its set up.. you perform test 5 between the positive battery post and the threaded stud out of the starter solenoid..

does your car still have the EECIV main relay and a fuel pump relay...

and you might want to .. if you have some jewelers headgear.. remove the computer and pull it out of its case.. closely examine it for cracked solder joints on the circuit board..

do you know what those look like?

[32 Chevy]

Hi Wayne, thanks, I was hoping you would chime in.

I will run those tests this weekend. I know just enough about EFi to be dangerous, but I'm glad to learn. I took about a perfectly good carb setup and replaced it with EFI partly so I could talk with the young bucks.

So clue me in about the EECIV relay - I believe the computer is in line to a fuse not through a relay. The fuel pump runs through a relay although it is an after market (bosch?) not a ford relay.

[kb426]

Your pony tank makes me nervous. Not having the vss can cause some idle issues but because you stated that it took 15 minutes before it would restart, it makes me think it is heat related. The coil, the tfi module, and the supply of fuel are the items that come to mind as being affected by heat. To answer the question about egr, if those items have been removed from your intake manifold, there is a aftermarket plugin that can be put into service that will tell the ecu that it's ok. If you find a block of relays that have more than 1, you should have relays for everything. Have you ever checked codes before this happened?

[32 Chevy]

Wayne,

I did your test and here are the results,:

Battery voltage, engine off after lights on for one minute= 12.4. This is a good, recent fully charged Optima blue top battery. Note that a blue top is a deep cycle battery not a starting battery.

Engine running, lights on:
Negative to positive battery voltage 13.6

Negative battery to block .01

Negative battery to body .025

Negative block to body .04

Positive battery to starter relay .04

Positive battery to yellow / white alternator wire .21

Positive battery to green / red alt wire .48

Positive battery to black / white alt wire 6.48.

Now what does that tell you?

[32 Chevy]

Your pony tank makes me nervous. Not having the vss can cause some idle issues but because you stated that it took 15 minutes before it would restart, it makes me think it is heat related. The coil, the tfi module, and the supply of fuel are the items that come to mind as being affected by heat. To answer the question about egr, if those items have been removed from your intake manifold, there is a aftermarket plugin that can be put into service that will tell the ecu that it's ok. If you find a block of relays that have more than 1, you should have relays for everything. Have you ever checked codes before this happened?

I agree that it must be heat related.

The coil is good quality Accel unit mounted on the fender well away from engine heat- I don't see any signs of spark tracking or cracking.

The TFI module is new - that was the first thing I changed when the stalling occurred.

What are your concerns about the pony tank?

Searching the  interweb there was a sugestion a bout the PIP in the distributor causing irregular performance when overheating. Any comment about that?

Dave

[wayne petty]

I checked the codes - 51, 67, 81, 82, 84, 95, 29 came up. Of those the one that caught my eye was 51; ECT sensor out of range.

51    ECT sensor signal is greater than the Self-Test maximum of 4.6 volts.

67   Neutral safety circuit failure. OR  A/C circuit was on during KOER Self-Test.    

81    Air management 2 circuit failure (AM2/TAD).
    OR MAP sensor vacuum was not greater than 2 in-Hg (7 kPa) during normal vehicle operation.

82     Air management 1 circuit failure (AM1/TAB) .

84    EGR Vacuum Solenoid circuit failure.

95    Fuel pump secondary circuit failure. The EEC senses infinite resistance to ground from the fuel pump on the Fuel Pump Monitor circuit.


29    Insufficient input from vehicle speed sensor.



lets look at how code 51 and the ECT sensor works..

one wire is grounded to the PCM.. the other wire has 5 volts on it..  the ECT sensor varies the resistance to change the amount of voltage on the 5 volt wire..  the device in the computer putting out the 5 volts is current limiting.. and the computer monitors how much voltage is left out of the 5.0 volts. this is what it uses for temp calculations..  with the code 51..  disconnect the ECT sensor and read the resistance..   plug the sensor back in and disconnect the ecm and ohm the pair of wires in a loop.. please be very careful to NOT damage the connector pins  in the ecm connector.. have a friend wiggle the harness at the ect sensor and make sure you are not having any changes.. ford wiring can get brittle after decades of wiggling..

normally.. we clear the codes.. disconnect the ECT..run the KOEO test..
see if it will set the code 51.. above 4.6 volts..  hook up the sensor and clear the codes..

key off.. disconnect the ECT sensor..  jump the pigtail perhaps using the pins from the previous ect sensor you have broken open to extract them.. and see if you can set a code 61 with the koeo..  this proves the wiring may be good..


PIN 46 is ground..  connected to the  ECT, ACT, TPS, EGR position sensor, both oxygen sensor, and if you have the EECIV test connector with the pair of cavities UP.. it will be on the short end of the connector..\


pin 7 should have the 5.0 volts on it.. that is variable as described above..
i usually just ohm the wiring harness while wiggling.. i do have 2 EECIV breakout boxes.. and stacks of manuals.

[wayne petty]

Wayne,

I did your test and here are the results,:

Battery voltage, engine off after lights on for one minute= 12.4. This is a good, recent fully charged Optima blue top battery. Note that a blue top is a deep cycle battery not a starting battery.

Engine running, lights on:
Negative to positive battery voltage 13.6

Negative battery to block .01

Negative battery to body .025

Negative block to body .04

Positive battery to starter relay .04

Positive battery to yellow / white alternator wire .21

Positive battery to green / red alt wire .48

Positive battery to black / white alt wire 6.48.

Now what does that tell you?

those all look great.. within spec...  and for those wondering.. why the bottom number is 6.48..  that is the stator voltage.. should be half the output voltage of the alternator..

[2rods]

Is the new TFI module aftermarket or Ford? I have had no luck at all with aftermarket and most mustang guys will say the same.

[enjenjo]

With the pony tank that small, I see the possibility of hot fuel returning to it to be hot enough to vaporize, making the high pressure pump receive only vapor.

I would suggest rerouting the return fuel to the big tank to give it time to cool before it goes through the system again.

[32 Chevy]

Ah, that is a great idea about the pony tank. I did notice that when I opened the hood after the engine stalled the underhood temp was real hot. The  water temp gauge was about 210 degrees but under the hood felt hotter. That could have overheated the gasoline in the return line.

I'll switch the return line back to gas tank and let you know if the problem goes away next summer.