intermittent check engine light

[marq89]

I just bought a 1989 Grand Marquis, this is my first Ford family product.

the check engine light comes on (flashes, never stays on solid) when i press the gas. Never when decelerating or at idle. Otherwise, the car runs fine. No misfires, sputtering or loss of power. Smooth idle and power.

Is there a way to check the codes without a reader? I am in Canada, the local garages all want to charge (about the same price for me to buy my own reader) to check the codes, $ is tight for the moment.

I know the TPS sensor was replaced by the previous owner, and i had to adjust the TV cable as it was shifting too late and way too harsh.

Do these cars have a pressure sensor in the gas tank?

Thanks,
Shane.

[1987cp]

You can check for stored codes (on a 5.0 SEFI car, anyway) by using a jumper wire at the EEC-IV connector located behind the coolant overflow tank and then sitting inside and counting flashes. Each sequence of flashes correponds to a code number, which you can easily look up in a Haynes manual (or ask someone on here to do it).

Some later box-body cars had two check engine lights, one to denote a stored code and one that's just connected to an low oil pressure switch and a high coolant temperature switch. The second one just tells you if you're overheating or your oil pressure is low. Can't hurt to toss a cheap coolant temp and oil pressure gauge on the car to make sure of what it's doing.

What do you mean by a pressure sensor in the gas tank? Are you thinking of some of the newer evaporative emissions systems that actually pull a slight vacuum in the fuel tank?

[marq89]

Hi, thanks for the info on the codes. I have 2 lights on my dash. One that looks like a picture of an engine (which i think is the oil pressure and engine temperature warning light) and one that actually says "check engine". It's the second one that lights up.

for the pressure switch, i have read that some cars will throw a code if the gas cap is loose or defective. As per info on ALLDATA.com for my car:

SEALED FILL CAP
The sealed cap incorporates a build-in pressure-vacuum relief valve. Fuel system vacuum relief is provided after approximately 0.50 inches vacuum is reached inside the tank. Pressure relief is provided when pressure inside the tank builds up approximately 2.2 psi. Under normal operating conditions, the fill cap operates as a check valve preventing vapors from escaping the tank through the cap.

I thought it might be that becasue the car manual says when unlocking the gas cap to hold the key for a second to relieve pressure in the tank. but mine doesn't work, i can unscrew the cap without unlocking with the key.

[marq89]

I've seen the connector before, which terminals on the connetor do i jump?

[marq89]

nevermind. I found the info on www.troublecodes.net/Ford

[gadget73]

That works, or http://fordfuelinjection.com/?p=6 has the info as well.

[1987cp]

Great, we shall await the results of the code reading (counting?) .....

Thain, any idea what he means by this locking gas cap routine? I hadn't though any Panthers came stock with a locking gas cap.

[gadget73]

not familier with a factory locking fuel cap, but it may have been some option I wasn't aware of. Possible it was available as a dealer part or something.

[marq89]

Well i went to go count the flashes last night after jumping the EEC (key on engine off), but nothing hapenned. I heard noises from the engine, i'm guessing the computer doing a self-test of the relays, solenoids, etc... but no flashes on the dash. the MIL actually went out, but wouldn't flash. Maybe i just didn't wait long enough.

Anyways, i'm going to bite the bullet and buy a code reader tonight ($50 CAD). Like I always say, "work smarter, not harder".

[1987cp]

I do seem to recall the light coming on for a period of time, then off for a pretty good stretch before it started flashing. But a code reader would definitely be more easier.

Sucks that you guys don't have parts stores that pull codes for free like we do.

[marq89]

OK, so I bought a code reader and hooked it up.

No codes in the KOEO self-test.
only 1 code (31) in the CM self-test
no codes in the KOER self-test.

code 31 is the EGR sensor.
With the engine running at idle I applied vacuum to the EGR which made the engine want to stall. As soon as vacuum was removed, the engine returned to normal idle. With the engine off I hooked up a vacuum pump to the EGR and it will retain vacuum for several minutes. So the EGR itself seems to be functioning properly.

But I don't know how to test the EGR sensor. I'm getting the proper 5volts refence to the sensor, but other than that i don't know what to look for.

Any ideas?

[88grandmarq]

http://www.grandmarq.net/vb/showthread.php?t=31462

code 31 is for the EVP sensor circuit being below minimum voltage.
even though you have 5v going to the sensor, the sensor is not reading correctly and sending an incorrect reading back to the ECM.

I would replace the EVP sensor.

[marq89]

Before I go and throw $80 at a new part, is there a way to test the one I have? I don't want to change it if turns out to be a wiring problem.

[88grandmarq]

http://www.fordfuelinjection.com/index.php?p=35

[gadget73]

Define "no codes". Do you mean literally no codes, or just the "11, all OK" code ? You should not have a no code at all condition, if all is well, it gives an 11.