Code Trifecta 31, 41, and 91

[TecNickal]

1990 Town Car w/5.0L

ON A COLD ENGINE.
Ran the codes for the car - received codes 31, 41 and 91.
31-EGR position sensor below minimum voltage
41-Lean Bank 1 per O2 sensor
91-Lean Bank 2 per O2 sensor

So I cleaned the EGR valve of carbon. no change :-/

Then I noted that I heard a HISSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS under the hood for 15 second near the brake booster. And I remembered that its grunts when apply the brake pedal. Typically 1990 model w/factory booster = it's bad.

So...due to the large vacuum leak from the bad booster, I received these three codes because the EGR valve is not opening properly, causing the car to run lean!.

How about that for diagnosis!

[gadget73]

31 usually indicates a bad sensor. It means its too-shut, which doesn't happen from vacuum leaks. About the only real way it happens is either the internal bits of the EGR valve have eroded away and the pintle is too far into it's seat (unlikely), or the sensor is dinked and the ECM has no idea what to do with it.

41 and 91 though, yeah, thats possible.

[TecNickal]

But 31 is just saying low voltage or out of range for the position sensor of the EGR...

[gadget73]

right, its low voltage out of range on the position sensor that bolts to the back of the egr valve. When the EGR valve is closed, voltage is low, it increases as it opens. When the output of the sensor is too low, it means the valve has physically shut too far, or the sensor is just bad. The ECM looks for a certain range of voltage to indicate that the valve is closed. If its not in that range it spits out an error code and disables egr function. Basically it operates like the TPS.

http://www.grandmarq.net/oldfuelinjection/page35.html

The EGR system is not as refined as later models. It has absolutely no clue whether the egr is really working, it can only tell if the valve opens or not based on output of the position sensor.

[TecNickal]

I don't buy that the sensor has closed beyond the threshold - I didn't loose metal. Unless somehow the pingle on the EVP has worn down? - I would believe it going bad. Unfortunately, my issue is actually at idle.

And I know there is supposed to be 0 EGR action at idle, so as long as the pintle is closed, it should be fine. Unless it's sticking too, causing additional air to enter. The car indicates it's running lean per EGR, but the car has richened the mixture to compensate for the lean.

Yesterday I worked with a good friend of mine doing some diagnosis on this car. The thing can't hold an idle when starting. You'll crank, it'll start, then die. You have to hold your foot into it.

Vacuum line for the MAP sensor is fine. Rubber is good and uncracked. Thinking I have a bad MAP, or an IAT that is coated in carbon, or a TPS that is not acting right. While cruising at just tip in throttle only like going 38 or 45 mph, the car will buck like anything. If the car sits and heat soaks, it's hard to keep the car running at idle at a stop light.

So I'll start swapping out the IAC, MAP, ECT, IAT, EGR w/EVP, and TPS after work from the 89 or the 87 and see what happens.

[DerekTheGreat]

...Thinking I have a bad MAP, or an IAT that is coated in carbon, or a TPS that is not acting right. While cruising at just tip in throttle only like going 38 or 45 mph, the car will buck like anything. If the car sits and heat soaks, it's hard to keep the car running at idle at a stop light.

So I'll start swapping out the IAC, MAP, ECT, IAT, EGR w/EVP, and TPS after work from the 89 or the 87 and see what happens.

I didn't buy it when the dudes on here said I messed up the timing on Ashley's car but they were right

Your car and my car are doing similar things yet at different extremes. When my car is cold and sometimes when hot the car will stumble when taking off or resuming throttle, and I mean if I just toe in the gas a smidge. Sometimes if I can hold that exact position it will do that for two seconds or so, all stumbly. I get the same stumble effect by applying vacuum to my EGR valve and based off of the code (I forget which one) it had something to do with the EGR, that it wasn't opening. It took well over 15inches of vacuum to get the thing to open and it doesn't do it smoothly. I've got a new one I'll be throwing on soon so we'll see if that changes anything. As for your situation, I'd futz with the EGR before I started throwing sensors and stuff at it.

[TecNickal]

So how's this for an oddball resolution.

The friend of mine helping me is a Ford mechanic from the 80s and early 90s. He said to toss on a known good MAP sensor first.

I'll be damned - the car started on the first turn, and it drives BEAUTIFULLY now. It's better than when I bought it, holy crap!! Exhaust smells fine. No check engine lights. Passes all OBD-1 tests. It runs GREAT now wow.

EGR and IAC cleaning I can see as regular maintenance. TPS replacement can make sence if there's a worn spot on it not sending signal to PCM. So now with a clean IAC, EGR, and all us taken care of - this car can head to the paint shop this week

[DerekTheGreat]

I'll be damned. No stumbling or anything? Did you swap out everything all at once or one at a time?

If my car still does the stumbly dance after the new EGR goes on I'll change out the map too. TPS can be checked by yourself if you've got some wire and a volt meter. I don't have the range in front of me but it most likely starts out very low, like 0.5 volts (there will be a range that's deemed acceptable at idle) and will steadily increase as the throttle is opened. If it twitches or goes erratic then that points to a toasted sensor. I'll post the ranges later if my troubleshooting manual has them.

[TecNickal]

Nope did things one at a time. Cleaning IAC I did before issue happened.

Cleaning EGR I thought would
Help, but did not.

So before I started just swapping every thing out, started with map. And voila worked on the first try. It does 0-60 perfect. No tip in stumble, no farting, no bucking. Nothing . Drives properly.

[DerekTheGreat]

That's awesome. I never thought anything would get this stumble to go away, I just wrote it off as old electronics showing their age and what not but if this works...

[TecNickal]

Tip in stumble can also be from a broken vacuum line hidden under the plastic sheathing had fixed a couple of cars from
This

[DerekTheGreat]

Locations?

[gadget73]

hm, usually when the MAP is bad, its so bad that it barely runs. Most of them run pig rich at idle just like if you'd pulled the hose off the sensor.

[DerekTheGreat]

Alrighty, so I'm digging through the "bible" Ashley sniped from ebay.. I've got tons of stuff like this in it (1988 Ford car/truck service manual) and if it's already been posted somewhere then someone can spank me. Or if you guys need specifics I think I can provide them but without further ado:

EGR position sensor:
D shaped plug, voltage reference pin (Vref) is the right most pin. Manual states you need to connect a vacuum pump to it and apply vacuum up to 10 in.-Hg (33kPa) while an ohm meter is attached to measure the resistance, which should gradually decrease from no more than 5,500 ohms to no less than 100 ohms and vacuum is gradually applied.

Engine coolant temperature sensor:
Upside down "Q" looking plug. With pins facing you the signal is the upper pin and the return is the lower one. Manual states that to pass the test the engine temp must be either: 1) key on, engine off with coolant between 50 & 240 degrees F 2) engine running, coolant between 180 & 240 F.
Using an ohm meter typical resistance between the two pins is: @50F: 58,750ohms , @65F: 40,500ohms , @180F: 3600ohms , @220F: 1840ohms.

MAP sensor:
Reverse facing "D" looking plug. Three pins, bottom is Vref & top is signal return.
Approximate altitude (Ft) of 0, the voltage output from the sensor should be 1.59v, +/- 0.04v. This voltage will decrease by 0.03v per every 1000ft above 0.

Throttle position sensor:
Two connectors shown here, I think mine is the "Q" shaped deal. Upside down Q connector's Vref pin is the leftmost one, with the top pin being signal return.
Manual doesn't state a range but states that with the engine off, key on the voltage at the sensor should be between 4 & 6 volts.

Hopefully this helps somebody

[TecNickal]

This thing couldn't hold an idle normally. It would buck, snort, die etc.

With a over 2 decade old car - anything can happpen I seem to end up with the odd cars...

And I will make a video showing common places to look that cause the tip in stumble on a 302.