Vacuum gauge readings- need help

[fireguy12117]

ive been trying to troubleshoot EGR codes for a little bit now and i seem to have taken one big step backwards on it all.

i have essentially rebuilt the whole EGR system by now, the last thing being the EGR valve itself. driving home today i got another CEL: 0401, 0455, and 0800. i cant find anything on 800, so i'm ignoring it for the moment.

i had a vacuum gauge on the truck for 2 days. i noticed very little vacuum being produced at highway cruising. 20in when idling, dropping to zero fast when shifting through the gears. the thing just runs like crap too, feels like misfires, bucking in low speed...

i've been chasing my tail for a vacuum leak. there isn't one. what am i missing?

i thought i read something about a plugged up CAT causing similar symptoms. i guess what i am saying is for the life of me i cant find a vacuum leak yet i keep getting codes on systems requiring vacuum and when i put a gauge on the motor, i get nearly no vacuum while driving- so i wondering if i am going about this wrong. im stumped

 

[modelageek]

you are talking about your 98 correct?. my book says the p0800 is a transfer case issue?....sounds like you have a vacuum leak. do you have any other issues that might be vacuum related?

 

[kimcrwbr1]

Is the vacuum steady at an idle if so you have no vacuum leak run the engine in neutral at 3500 rpm it should read around 20 also and let off the throttle quickly it should go up around 25 to 28. If your losing vacuum at higher rpm it could be either egr opening too far plugged exhaust or valve lash sticking lifters. http://www.therangerstation.com/Magazine/Summer2003/VacuumLeaks.htm click on this link it shows you how to read a vacuum guage. GL

 

[kimcrwbr1]

To check the exhaust put your hand over the tailpipe and have someone give it gas the gasses coming out should increase in relation to the throttle position you will notice the difference if it stays the same you have a plugged cat or muffeler you can take it to any muffeler shop for a free inspection. Also plug the tailpipe with your hand or something you should be able to almost stop the motor if not you have a leaking exhaust. If you are not sure how old the cat and muffeler are now would be a good time to replace them and start saving money on unburnt fuel in my opinion but most shops will only replace what is necessary.

 

[fireguy12117]

thanks for all the feedback.

i repeated all the tests. i took everything off for vacuum lines except the FPR. I ran the engine parked, took readings, everything seemed normal. 22in at idle, increase to high RPM's, 20in or so. took it for a drive, drove fine. cruizing i had around 10in average, dropping to very low when accelerating, back to 20 when off the throttle.

started adding back in the vacuum lines. saw the vacuum drop a tiny bit, and i don't know it it was because i was trying hard to see, but thought i saw vacuum dropping when EGR was called. anyhow, Still getting CEL's for the insufficient EGR flow and drivability kinda of gets worse with everything hooked up, so right now it looks like im chasing a vacuum leak in the climate control system and or the EGR. which floors me...

climate sure, never really looked at it much, but holy jeez, im about to just run without EGR and say to hell with the CEL.

 

[fireguy12117]

so that was a kick to the head.

$1.29 later and a new PCV valve and we're rockin and rollin.

granted, there was a cracked EGR tube and probably some poor vacuum lines but all in all my intermitten hard to troubleshoot vacuum was a 2 piece PVC that had loosened up at the stamped seam. i hit it with brake clean and almost stalled the motor.

 

[jonbdeast]

Where is this 2 piece PVC located? And did this fix your problem, or combination of other things?