91 Grand Marquis start then stall

[HATNINJA]

fresh meat i checked the map hose and replaced the map and thats a good idea bout the dist you suggested but i replaced the mod and pickup. i have the puter about out ran out of day light im gonna replace it then if it dont fix it ill look for shorts. man we are gonna be alot smarter when we figger it out then ill take pics for yall.

[Freshmeat]

Dig to the back of the lower intake manifold. There is a ground bolted to the rear driver side bolt of the lower intake. If that is shorted out it can overload your ECM in no time. Even if it's only slightly broken, I'd put a new fitting on the end.

Also, on the battery ground there is a black connector on a ~12ga wire. Cut out that connector and splice the wire back together without it. Those are the two main grounds. See if either of those help.

[HATNINJA]

ok ill check those out in the morn
thanks dude

[HATNINJA]

hey man do you know where i can find a pic of the ground on the intake will it be visible or is it buried

[Freshmeat]

I JUST got mine going after it sat for four years. If not for the guys here it would still be sitting in the weeds. If I can think of anything else to check I'll post it up.

The one behind the manifold seems hardly likely but it gets weak, then you put one good tug on the PCV hose or O2 connector and BOOM, it's done. It can generally ground elsewhere in the system, but it can also just as easily short out something else, like the ECM.

Have you checked your TPS voltage? At KOEO orange should be around 5v and green around 1.00 - 1.15v. As you open throttle to WOT (car off) the green should climb to about 4.9x - 5.00v. If it doesn't, disconnect the TPS and check the feed plug to make sure the wire feeding the orange is putting out the ~5.00v. If it is, replace your TPS. If it isn't, replace your ECM.

[Freshmeat]

You can see it. Use a flashlight, but it shouldn't be buried. If you don't see a wire attached to the lower intake it may have broken off. Dig around the harness laying across the top of your bellhousing and see if you see a lone wire hanging out not attached to anything.

[marquisman]

its just weird that his car will run if you hold the throttle open a bit...

[HATNINJA]

yes it is frackin wierd

[Freshmeat]

Also... and this may be a long shot being that you can at least get it to start... pull a spark plug wire at the plug, stick a screwdriver (plastic or rubber handle) into the boot, and hold it against the alternator bracket while someone spins the motor over. See how far the spark can jump. It should literally be able to jump about half an inch, and per Thain, it should be a blue spark. Yellow/Orange spark is weak. If it can't jump about half an inch it's too weak and you need a new coil. That ended up being the final problem in my puzzle.

Just because it'll spark 1/4" or so in the atmosphere (outside the motor) doesn't mean it'll spark under correct compression.

[gadget73]

the yellow and red wire sounds like the fuel pump relay. Don't jump that. It tests the fuel pump, but it won't test the wiring from the ecm out to the relay. Grounding that pin in the self-test connector will test the relay and the ecm wiring. It should give the same result though.

I'd like to see a fuel pressure test. That would tell you if the pump has crapped out, or if something is massively clogged. Since it starts and dies in a couple seconds, that sounds like its running out of fuel even with the fuel pump hotwired. If you haven't replaced the fuel filter, that may not be a bad thing to try.

It may also be a bum TPS causing the ECM to think you're in flooded start mode. That will give the engine no fuel, so it won't start. If you have a voltmeter, check from ground to the green wire. Use a paperclip or something to backprobe the connector. You should see around 1 volt with the key on and throttle closed. That should increase smoothly to around 4.6 volts with the throttle wide open. If it doesn't do that, then the TPS has bailed out on you.

[Brandon]

I know this is a rare thing to happen, but could a faulty fule injector cause this? Or would it still run but run very weak?

And yeah the fuel filter wouldn't be a bad idea to change out.

[86VickyLX]

I know this is a rare thing to happen, but could a faulty fule injector cause this? Or would it still run but run very weak?

And yeah the fuel filter wouldn't be a bad idea to change out.

Depending on how it failed, t would cause an extended crank issue, a drop in fuel pressure and a drop in MPG.

[gadget73]

one injector won't cause that. I have purposely unplugged a single before though and it makes almost no difference. If you ever run a cylinder balance test with the ECM, it shuts off one at a time and you can barely tell unless you listen close. A leaky injector would show up as running rich and one or two wet black plugs. Would probably still start and run, but crappy.

[HATNINJA]

Well guys i just ordered a puter off ebay be a few days cross your fingers. hey gadget i did ground the wires on the self test connector also it was before i tried the other way i grounded the two wire terminal and it didnot run the pump does this mean that it probably is the puter or a wire to the puter?

[Freshmeat]

Did you check your voltage at the TPS?