I was referring to the A4LD vac. mod. in the pre 96

my 96 has the CC vac. servo.

the extreme under hood temps on these Aeros contribute to the short life of the vacuum lines. I've had the fiberglass hood so hot on mine that it burned my hand trying to open it.

the floorboard sauna is the main reason we dumped it as a tow and vacation rig.

 

Most of those plastic vacuum lines break in the engine compartment, as that's where all the heat originates. So I would look for breaks there. But not knowing any more, plugging any broken or cracked lines you come across would be a good first step in diagnosis.

Those that have vacuum lines going to the transmission and cruise control will use rubber lines that are far less vulnerable to heat cracking than those plastic lines. But it's a good idea to check them anyway.

In my van, I had a line and cap pop off of the vacuum tree at the rear of the intake plenum due to backfiring. It caused rough running and lit up the check engine light. I have since replaced two of those caps with a line looped from one nipple to the other, and one of those connection is very loose. When one of those caps popped off, it was impossible to find. But when the next backfire pops off the loose end of the line, I can push it back on with little effort and be on my way.

 

Shoot; nothing conclusive learned by bypassing the 3-way vacuum tee which appears to branch off to the A/C system as well as the heater system. It won't even die consistently now when turning the heater control with line connected and engine warm. I think it died once when bypassed; several times it did not. I haven't looked at the tranny vacuum line yet. There is a line loose that should go to the cruise control but it has a check valve in it, and it doesn't draw any vacuum.

I finally ran the engine warm with MAF disconnected; no noticeable difference, including at higher revs. This suggests problem with MAF, yes? I'm pretty sure it's the wrong one for the vehicle based on the P/N.

92

 

Update; took it for smog. Failed, HCs through the roof. Recommendation from my trusted smog guy; run a compression test first, paying close attention to plug condition, then look at other ignition parts. Told him about the likely wrong MAF and he said yes, possibly. I'll hit it hard Wednesday and report progress,

92

 

running too rich.
MAF
or
front O2 sensor

 

UNBELIEVABLE. I went to run a compression check yesterday and neither of my 2 gauges would thread into the plug holes. So I decided to check plug condition at least. First 4 looked perfect. Went to pull #3 (rear of engine, pass side) AND FOUND THE PLUG WIRE DANGLING! NOT ON PLUG! GOOD GRIEF. From condition of the wire where it contacts the plug, it had been this way for awhile. Of course the plug had oil and no normal white color. Replaced both plug and wire; now no part throttle shake and you don't gag to death if you're anywhere near the tailpipe.

Man, it never felt or sounded like a dead miss. It drove like a complete pig but I figured I'm used to a 2007 FWD 4 cyl Nissan Sentra, so what do I know? It ran pretty smooth at both idle and around 2500 RPM; only that part throttle flutter was noticeable. And the HCs through the roof. I guess the fuel injection and engine management system compensate as best they can. Not like my old tired Mopar 440 that would periodically and sequentially oil foul the plug in the same two cylinders over and over; THAT was noticeable. I just carried a couple extra plugs and when I felt/heard the thing miss I would swap the plug and go.

So it's a bit embarrassing but I gotta come clean and let people know 'cause this is all about learning. And lesson learned; don't take anything for granted on a complex system. Now it's back to smog for re-test and hopefully good news. --

92

 

Always check the basics first...

 

True 'dat. Just brought it back from re-test; PASS! Let me rephrase that; EPIC PASS...HCs WAY under the limits now...NOX went up a bit, guess it's normal when you change something. Runs great now; idle just needs to come down a bit now that all 6 cylinders are contributing. Has a water leak, I think the water pump. We'll see.

I want to thank all who helped me with this; all steps taken were necessary and much learned. Hopefully my adventures help somebody else, especially the ECT stuff. VERY happy that I don't have to replace the MAF. And one more Aerostar saved instead of scrapped, which is where it was heading. These Vulcan engines aren't bad. --

92

 

Yah, dangling impossible to see Aero spark plug wires are like sex in the dark, gotta do alot of reaching touching and feeling.