Engine light on dash flickering when revs drop low?

[Maj]

A little advice please.

1984 302ci Grand Marquis

What sensors would the engine warning light be hooked up to? I'm trying to figure out why it's started flickering at low idle.

Appreciate any suggestions

[1987cp]

Most likely the oil pressure at idle is a little low. You can hook up a real gauge to make sure of exactly how low it's dropping.

[gadget73]

Prob low oil pressure as mentioned. if you can verify it with a gauge, try a thicker grade of oil. Not much to be done for it though, most likely the main bearings are wearing out. Keep oil in it, and don't worry too much about it. They run a long time like that.

[88grandmarq]

change the engine oil ... use some 10w40 or a 15w40. might even try a bottle of Lucas oil stabilizer.

[Maj]

Thin oil sounds like a likely answer, on turning off the motor I can hear oil dripping back down the block and is sounds like water. I did have it changed quite recently though, maybe it was low grade and has broken down already or just not viscous enough for this motor, it is 10W30.

Just to confirm guys, my GM has both an "engine" warning light and a "check oil" light, does the check oil light only sense the oil level? And low oil pressure is shown by the engine light like it's doing now?

I've got a tin of oil stabiliser, I'll try that today after I've given her some new plugs, leads and dizzy cap with rotor arm which I've been looking forward to doing all week

Thanks for the advice guys, it's great being on forum where people are so helpful

[marquisman]

the oil pressure is linked to your check engine light. the low oil light is hooked up to a sensor that is on the oil pan that tells you if your oil level is low in the pan. the check oil is an orange caution light where as the check engine is a red warning light.

[Maj]

the oil pressure is linked to your check engine light. the low oil light is hooked up to a sensor that is on the oil pan that tells you if your oil level is low in the pan. the check oil is an orange caution light where as the check engine is a red warning light.

Thanks again! I learn something new each time I'm here

Are there any internet sources for an owners handbook for the Grand Marquis '84? That might save me bothering you guys with some of the more simple questions.

[marquisman]

you can try to buy one from e-bay or a private site.

[1987cp]

I got mine for my '87 from a Ford dealer. That was in about 1999, though. Honestly, there isn't that much useful material in the owner's manual; it's most useful to look good to go with the car.

[91waggin]

the oil pressure is linked to your check engine light. the low oil light is hooked up to a sensor that is on the oil pan that tells you if your oil level is low in the pan. the check oil is an orange caution light where as the check engine is a red warning light.

To avoid confusion, I thought I'd point out that the red light is labeled simply "ENGINE". The "CHECK ENGINE" light is yellow and appeared on our cars in 1989 as an engine computer malfunction indicator.

[Maj]

OK then, finally got some GMN time for an update!

After changing the oil for some thicker stuff and the problem still being present i did some serious GMN searching. It seems I have a common problem: Car runs beautifully when driving but at idle it's rough as a bears ass. It idles perfectly for a few seconds then stumbles and shakes a bit before smoothing out again for a few more seconds. It is definitely missfiring on a number of cylinders when it does this. It is very rythmic too: 'stumble-smooth-stumble-smooth-stumble' and it only does this when it's warmed up. I've checked for air leaks, checked it's not over heating, replaced the plugs, leads, dizzy and rotor arm and I've cleaned all the wiring connectors. Problem still there!

The old plugs were all in good condition with good colour BTW suggesting the cylinders are all in good working order and the problem appeared overnight not gradually.

Yesterday I bought a new ignition pickup, Oil pressure sender, water temp sender, coil and an ignition control module. I'll start out by installing the sender units and ign pickup and see if that helps then try the new coil. While I'm under there I'll see if I can spot the 0xygen sensor which I will also try before the ICM because I can't return the ICM unit if I've used it and it was expensive. I'm not sure if the 02 sensor was removed when the propane system was installed though so can anyone tell me where to look? '84 Grand Marquis.

I'll let you know how it goes

[gadget73]

Oxy sensor will be on the passenger side, threaded into the back of the exhaust manifold.

Is this a CFI car or a carb car? Canadian models are slightly different, usually they had carbs where we got CFI in the states. If its CFI, I'd suggest checking for codes. You may also have a sloppy timing chain. The early models had plastic teeth on the cam gear, and it would get really sloppy. Pull the distributor cap off, and rock the crankshaft back and forth with a breaker bar. You should get nearly no movement. If you can rotate the crankshaft noticeably before the rotor moves, I'd be leaning toward replacing the timing chain. Its been known to fix wierdo CFI problems in the past. CFI cars get real cranky about slop in the chain.

[Maj]

CFI or Carb?

Neither Propane regulator, but originally carbed.
I am going to be working on the dizzy today so I will check the timing chain slack.
Thanks for pointing out another possible cause

[marquisman]

my 81 merc would do the same thing when i got off the hiway then stopped at a light. did it for years,i just got used to it.

[Maj]

My mechanical sympathy won't let me ignore it! Wish I could but when something ain't right on my car/truck/bike I just have to fix it