MAP issues (P0108)

[Nad_Yvalhosert]

Dorman 90449 Vortec Distributor Repair Plate Compatible with Select Models https://a.co/d/bpmpFWs

 

[454cid]

Dorman 90449 Vortec Distributor Repair Plate Compatible with Select Models https://a.co/d/bpmpFWs

You found it.... and for not as bad of a price as I was thinking, either.

 

[mudpie]

For the sake of anybody searching in the future, best I can find is that the original cap screws (GM part #10475922) can be replaced with an oversize screw (GM part #10457666). I would assume that just makes the problem bigger at some point. If the distributor holes stripped with small bolts, they're going to strip with bigger bolts. I see that as a temporary fix, though it might be several years worth of temporary, until the next time you need to unscrew the cap.

The Dorman part looks promising, but damn...somebody is making a fortune stamping those out in China, and getting 20 bucks a pop. And if I need it today, $30+ at my local parts stores. I've also seen it suggested to put 2 small studs in the distributor, with various combinations of Loctite or epoxy (JB Weld?), and never have to deal with it again. I can get a couple little studs at ACE hardware for probably 27 cents.

For now....zip ties to the rescue

 

[mudpie]

Cleaned the plugs, tightened up the cap, still runs like crap.

So it idles ok, but I've also come to realize that if I hit the throttle slowly I can get the RPM's up to 3 or 4k no problem. And if I mash the throttle at 3k, it'll jump. But if I mash the throttle at idle, it dies. That's got to be a vacuum leak, right?

 

[Schurkey]

if I hit the throttle slowly I can get the RPM's up to 3 or 4k no problem. And if I mash the throttle at 3k, it'll jump. But if I mash the throttle at idle, it dies. That's got to be a vacuum leak, right?

No.

That is, maybe it's a vacuum leak, but it wouldn't have to be.

1993 Lumina, 1600 miles from home. Holiday weekend in a minor mountain range--heavy traffic, lots of boats-on-trailers clogging the uppy-downy-twisty-turny highway. Runs at steady 70 mph with the most gentle misfire. Hardly noticeable--but terrible throttle response to anything other than steady throttle. Anything below 40 mph, and the engine almost always stalls. Hard to re-start. Damn miracle if it will move the car at all without stalling. IF I can get up to highway speed...runs at 70 mph with only the slightest, hardly-noticeable misfire.

Took me 8 hours to drive the final 130 miles to Dear Old Dad's house. Most of that time, stalled on the side of the road, trying to re-start and roll, only to stall again.

The folks who fixed the car, told me the fuel pressure was down from the spec of 40+, to about eight psi.

So, again, what is your fuel pressure, and how old is the fuel filter?

I'd also connect a scan tool, verify all the sensors but especially look at IAC, coolant temp, short- and long-term fuel trims, and MAP.

Have you tested coil output by using a spark-tester calibrated for HEI? Heavy and/or sudden throttle opening increases fuel demand, and also demands increased spark voltage. A weak coil will stall an engine when the throttle is popped open.

 

[mudpie]

I pulled the hose off the brake booster and it was holding a vacuum. I presume if I had a vacuum leak, the vacuum in the booster would have bled off, right?

 

[HotrodZ06]

Have you checked the crank sensor pigtail to see if the insulation is off the wires possibly making an intermittent signal loss?

Not sure but something else to check.

 

[mudpie]

I haven't. I will.
It's getting to the point where it barely runs now, so I'm checking every plug on every sensor. It won't rev now, and idles for maybe 4 or 5 seconds and dies. I keep getting the P0108 code (MAP sensor), but I've swapped in 4 MAP sensors with no change. They're used, but I can't believe all 4 are bad.
It's about time to put brakes on the Ford and drive that, but I don't wanna...

 

[Schurkey]

I pulled the hose off the brake booster and it was holding a vacuum. I presume if I had a vacuum leak, the vacuum in the booster would have bled off, right?

If the BOOSTER had a vacuum leak, the vacuum in the BOOSTER would bleed off.

A vacuum leak anywhere downstream from the booster check valve would have zero effect on the reserve vacuum held inside the booster.

You have zero vacuum in the engine/intake manifold when the engine is shut off. Think of the throttle blades at curb idle as being a huge vacuum leak. But the brake booster should hold vacuum for days.

It's getting to the point where it barely runs now, so I'm checking every plug on every sensor. It won't rev now, and idles for maybe 4 or 5 seconds and dies. I keep getting the P0108 code (MAP sensor), but I've swapped in 4 MAP sensors with no change. They're used, but I can't believe all 4 are bad.

Stop screwing with "codes" and start looking at live data. What is the MAP sensor showing when the engine starts 'n' runs, vs. when the ignition is on but the engine is not running? Does the thing show changing vacuum levels? Is the sensor signal flat-lined like the wire harness is damaged?

What is the service-manual procedure for your vehicle and a P0108 code? Service manuals can be downloaded for free from this site.

 

[Pinger]

mudpie@ read post #15. That's the direction of travel you need to be on.