I started having this problem about a week ago, maybe a little bit longer, but I didn't hook up my laptop until then.

Anyway, when I rev my motor the MAP value spikes to where it should be then starts to taper off. It seems like it takes longer under load, but it goes down really quick with the car in neutral or park. I used to hear a slight sucking sound which I figured was a vacuum leak [I traced it to an uncapped AIR fitting after the work].

It does this all the time since about a week ago. I figured I had a vacuum leak somewhere because of the PO completely rigging up the EGR and EGR solenoid. I've had it disabled in my PROM for a couple of months, so I figured it was finally time to get rid of the EGR completely.

I took off the plenum and runners, switched to 16k mile take off LT1 injectors since the stockers had 160k miles on them, made an EGR block off plate [which seals well, no leaks], cleaned the carbon out of the plenum and runners [ran out of time to port them], then buttoned everything back up with new gaskets.

Off the farthest back vacuum line on the pass. side I have the MAP sensor, next is the line for the AFPR, then comes the line for the Cruise/HVAC line. All seal well. I also capped off the vac. fitting for the EGR behind the throttle body and the brake booster is hooked up as well.

After taking it for a test run last night I figured that it must be the MAP sensor since I was still getting the same results. I ran over to CarQuest today and picked up a new MAP and am still having the same problem.

The car still runs well even with this problem, I might even say it feels stronger then before, but the butt dyno has been known to lie. The main problem it causes is my knock went from ~25 counts in a 15-30 minute period, to about 250-400. It's just frustrating because I didn't have this problem before and I know this isn't how the car should work. FWIW, I'm running a slightly modified Super AUJP bin.

Sorry about writing a book on it, but I didn't want to leave anything out. Any help is greatly appreciated.

PS- I posted this in DIY PROM because the only reason I noticed this was the problem is because I did some datalogging.

 

Ideally, the MAP should have it's own fitting, a short copper line, and be close to the vac fittting. Just sharing a fitting with something else can dampen the signal it needs to see.

If you do that, and have not other problems, then what you see is what you got.

Thou, vac leaks can be a major grief causer.

 

I think I've written up two posts now that I've forgotten to actually click send on.

I'm not sure how or why, but it seems like my vacuum leak has gone away. I did rotate the tubing connected to the MAP, so that must've done it. Very annoying though.

I guess the knock I'm getting now means I just have to re-tune. I'm almost positive I had a runner leak now. The load values seem to be at least 5-6kPa lower at idle now, and the throttle can cause much smaller changes then before. Maybe it's a combo of fixing the leak and a new MAP.

Anyway, I was always so fixated on the knock counts, retard, and load values that I never bothered to look at my TPS voltage. It maxes out at 1.72v, definately in need of a recalibration or replacement. I guess that'll happen after 160k miles.

Thanks for the advice, Grumpy, but my line is only about 3" long, it's thick wall vacuum tubing, and it's the only item on that port. I highly doubt the line is collapsing.

I do agree with vac. leaks being a PITA though.