'87 Colony Park, stutters, bucks, and stalls. Help Pls!

[jaywish]

It would be typical for the engine to run worse when this in unplugged so I suggest trying that.

IIRC it could be a vacuum leak, bad harness or bad sensor.

On another concern, the car does not pop back into the intake?

[sly]

Yeah... if the hose to the MAP sensor is crap, replace it. That could be the entire issue. If disconnecting the MAP does nothing or it runs better, the MAP sensor is toast.

[jeff97062]

sensor, yes. firewall, above and behind the passenger side valve cover usually.

I have had one go bad, and the engine ran extremely rich. Oddly it ran normally when unplugged. My best guess is the diaphragm inside broke and for whatever reason the position stuff sits in with vacuum and working is approximately the same position it sits in with no vacuum and broken.

Okay, will check that out. I thought mechanic changed the MAP. But that's the downside of doing some with mechanic, some by yourself. You don't always know for sure.

Thank you for the advice!

[jeff97062]

One final thought on fuel pressure though, the issue is, even at WOT its still around 30. Shouldn't it be close to 40?

[jaywish]

After simple check of Map,

Does it backfire through the intake?

Check the throttle base setting.
Check firing order is NOT HO.
Make sure ECM is NOT HO.
Are you 100% sure the engine is not an HO? Could it have been changed in the past?

[jeff97062]

No, I have no idea if it's HO or not. Model is 1987 Mercury Grand Marquis Colony Park LS. The WINis 2MEBM79FXHX656764. Most of this is obvious, but not sure what you want to see to know if it's HO. Here's what the specs say on a VIN check:

Displacement(CI): 302
Other Engine Info: Cental Fuel Injection
Displacment (L): 5.0
Engine Power (kW): 111.8550
Engine Configuration: V-Shaped
Engine Number of Cylinders: 8
Engine Brake (hp) From: 150
Displacement (CC): 4948.893328
Engine Brake (hp) To: 160
NCSA Model: Marquis/Monterey (car version; for van version 2004 on see code 444)/Grand Marquis

[jaywish]

Ho (high Output) Motors, available in mustangs and Lincoln mark VII are very similar same size engines that are sometimes swapped into panthers. They have different internals and heads. perhaps most significantly here the camshaft requires a different firing order. And a different engine program in the ecm. So there are two 5.0 liter ford motors in the same years with two different firing orders and ECMs. I have seen people use the wrong order when installing new wires. Just something to check. If it is the original engine it requires the Non-HO firing order.

[gadget73]

If the fuel pressure jumps from 30 to 40 when the vac line is removed, the reg is fine. At WOT it may not actually show an increase at peak fuel demand, depends on how healthy the rest of the system is. Either way that won't be why it idles badly.

[jeff97062]

You know, now that you mention it, the mechanic said he changed the firing order. He may have mistakenly changed it to HO, assuming it was same as foxbody 5.0 mustang. So today I'm going to check the following:
1) MAP and MAP line - disconnect and see if if run different.
2) Review firing order through dizzy into cylinder, make sure it's set for NOT HO

Hey, GrandMarq gang, thanks again for all the info on my beast! This is exactly why I buy project cars, to try new stuff (to me) and learn!

[jeff97062]

I don’t know what u mean by pop back in the intake manifold. Do u mean are both end connected? Sorry for dumb question

[jeff97062]

I disconnected MAP hose and it died. MAP was definitely replaced also. Doesn’t mean it isn’t failing, just stating it as a fact after inspection.

[jaywish]

The opposite of a backfire. Small engine explosions into the intake.

[jaywish]

When installing wires make sure they particular ones are crossed as shown if you look very closely at diagrams.

[sly]

Looks like the MAP sensor is fine. It did what it should have done. We can probably rule it out as an issue.

[gadget73]

yeah if it didn't magically start running like normal, the MAP isn't dead. Normally when those are unplugged the fuel goes super rich and usually it dies, or at least runs completely horrible.
They rarely fail in some sort of not-dead manner. There is a way to check it with a tachometer to verify frequency output is within spec but if its already been replaced and didn't change how it runs, I'll vote "not it".

personally I'm not much for throwing parts at a problem without diagnostics, but it sounds like thats what has happened here. At this point its hard to know if the original problem remains or if there are new problems introduced.

[jeff97062]

I replaced the vacuum tube into the MAP, to no difference. but then I got out the multimeter to check wiring to the MAP. It's got 7 volts going to it, when I believe it should have 5. The rating of ground to signal is supposed to be 1.4 to 1.8....and it's 2.05. Could bad wiring be the source of the issue? My fuel injection was rewired by the shop because mice ate the wires through them. When they replaced that, is it possible that jacked up my wiring to the point it did this? I have a new motorcraft MAP coming in tomorrow, in hopes the Duralast MAP they put in is just crap....but not convinced it will solve anything.

[gadget73]

what were you using for a ground connection?

[jaywish]

The map test you did indicated probably good as sly and Gadget mentioned.

Did you check the fire order?

The injector wiring could also be an issue but first check the fire order.

BTW could you send a pic or two of the engine?

Also does it pop back through the intake?

[jeff97062]

Yes, I checked firing order is SO 5.0. I tried both(HO and SO) to be sure even, but SO works.

See pics, as you requested.

Lastly, how would I check to see if it’s firing back thru the manifold?

[jeff97062]

having trouble posting image...