Car won't stay in closed loop, getting my but kicked

[Ranchero5.0]

A little history... Car ran fine until I tore it down over Xmas except it blew the head gaskets all over the place. Found the exhaust valves got in a fight with the pistons because AFR didn't hone the guides right when new. Fixed that and put it back together after finishing the port work on the lower intake. Electronicly it was ok, now it's dropping out of closed loop after it heats up, or sometimes it just doesn't go closed loop. When in open loop it idles around 1300 and the A/F stays slightly rich, plus it'll surge when cold. Coded it and fixed everything that came up (mostly EGR's EVP not reading correctly). When I tore it down I left the ten pins connected and just draped the harness over the cowl like I always do. Twice while KOER coding it it was running in failure mode (open loop), but didn't have codes. You get a failure mode indication when the cylinder ID mismatches on the scanner while testing.

So far I swapped the EGR system (valve, EVP sensor, solenoid) and plugged the ECT into a spare sensor. I have to pop the upper off to swap the ACT out. I'm going to do that today and look for damage under the upper intake with the wiring. I'm good at isolating these problems, but this one is really kicking my behind.

I have to swap out a water pump on a customers '95 lightning today (need a break from the stang). The ranchero is sitting next to stang so I can swap parts back and forth, but I'm running out of ideas or reasons why it's acting up.


Jamie

 

[PRO50SC]

What do you mean by you plugged the ect into a spare sensor?
I'm under the impression that your ect is hooked up to a spare sensor and just hanging aimlessley under the hood somewhere. If this is correct, this would be the reason for no closed loop and why the car is running rich. The ecm can't read engine temp and still thing the engine temp is cold therefore creating the rich mixture and the open loop. More info needed.

 

[rd]

A little history... Car ran fine until I tore it down over Xmas except it blew the head gaskets all over the place. Found the exhaust valves got in a fight with the pistons because AFR didn't hone the guides right when new. Fixed that and put it back together after finishing the port work on the lower intake. Electronicly it was ok, now it's dropping out of closed loop after it heats up, or sometimes it just doesn't go closed loop. When in open loop it idles around 1300 and the A/F stays slightly rich, plus it'll surge when cold. Coded it and fixed everything that came up (mostly EGR's EVP not reading correctly). When I tore it down I left the ten pins connected and just draped the harness over the cowl like I always do. Twice while KOER coding it it was running in failure mode (open loop), but didn't have codes. You get a failure mode indication when the cylinder ID mismatches on the scanner while testing.

So far I swapped the EGR system (valve, EVP sensor, solenoid) and plugged the ECT into a spare sensor. I have to pop the upper off to swap the ACT out. I'm going to do that today and look for damage under the upper intake with the wiring. I'm good at isolating these problems, but this one is really kicking my behind.

I have to swap out a water pump on a customers '95 lightning today (need a break from the stang). The ranchero is sitting next to stang so I can swap parts back and forth, but I'm running out of ideas or reasons why it's acting up.


Jamie

Sounds mostly like the computer is not getting one of the signals it wants to go closed loop. Temp sensor would be my first guess, then perhaps the egr stuff. I have 96, 97, and 02 Fords, and every one of them has had the DPFE sensor fail. A thermostat staying open will do this. Just getting into the computer stuff, as I got the scan tool for Christmas. Can you check the sensor inputs while it is running to see the values, regardless of code status. That seems to help me. It almost has to be a lack of sensor input.

 

[jrichker]

Looks like it's time to probe the voltages from the ECT and ACT at the computer.
Check the following:
Pin 26 = Vref should be +5 volts +/- 5%
Pin 25 ACT signal in. at 50 degrees F it should be 3.5 volts. It is a good number if the ACT is mounted in the inlet airbox. If it is mounted in the lower intake manifold, The readings will be lower because of the heat transfer. Here's the table

68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .8 v
194 degrees F = .61

Ohms measures at the computer with the computer disconnected:
50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 Kohms

The ACT & ECT have the same thermistor, so the table values are the same
Pin 7 ECT signal in. at 176 degrees F it should be .8 volts

 

[Ranchero5.0]

Pro, just plugged it into a spare to see if it would change the symptoms.

RD Puter doesn't seem to care about temp. Does it cold or warm after idling or on starup, cold or warm. I monitored the Vref last night as the motor warmed up hoping something would load it down, but it stayed rock steady at 4.99vdc. The grounds are fine. Puter seems to have problems with the o2's in closed loop, really slow to sweep and drops off the gauge lean for a second or two in closed loop. Never did that before. I'm going to swap the A/F over to the other o2 and see if it's acting the same. I don't expect anything major because when I put the A/F gauge on six months ago one of the o2 leads was broken in the harness and the puter still ran fine on one o2.

I did run almost a half tank of fuel out of it troubleshooting it, very bad. Finally noticed the fuel pressure dropping off and had to beat feet to the gas station with the motor cutting out. Did run ok until I got home and it seemed and stuffed it into the garage and away it went.

Jamie

 

[Ranchero5.0]

J, thatnks for the tables, PITA to pop the puter out for back planes though. One thing that I did play with on this rebuild was the 1262's don't have EGR provisions so I drilled a 3/8" hole in the gasket. Wondering if it isn't enough or if it would even make a difference. I have to run some errands later so I'll go scan it again for S+G's

Jamie

 

[Ranchero5.0]

Ok, today I swapped out the distributor and even put a C+L 73mm meter on and it stayed the same. Tonight I ran down a set of used o2's and swapped them out and it seems to have went away. I remember taking them out of the headers so they wouldn't get banged around when the heads came off. Unfortunently they sat under the car and got drenched in antifreeze when the heads did come off. o2's hate antifreeze... My own brainfart may have done me in. The A/f is responding much better now and the car seems happy. Perhaps it's a case where the sensor wasn't telling the puter what was actually going on and I thought the sensor was saying the truth.

Jamie