Ok I understand what your saying now. I just read it wrong.

 

ok, its not a cracked head, truck ran fine when pulled into the shop. i drove it 500 miles after i had pulled the cat and the truck hadn't changed at all. issue has only occured since after repair. compression 120 psi in cylinder #8 all others are within 10%. vacuum at idle 18hg" 2500 rpm jumps to 22 drops back down to 18hg" map sensor: output at idle 1.45 volts, alldata spec 1.5-2.1 so guys, any ideas now?

 

What do you mean by "at idle 18hg" 2500 rpm jumps to 22 drops back down to 18hg" ? It drops to 18 while holding 2500, or after you let off the throttle?


Anyway, as already stated, I agree to route the wires according to TSB . http://dodgeram.info/tsb/1998/18-48-98/18-48-98-v8.htm

And check that wires are seated on cap and plugs(maybe pull and replace 38 wire and plug) Also check that the injector plug is seated(and or wire is not damaged) and that the orings were not damaged.

 

plug wires have already been re-run to that diagram. cylinder 8 has plenty of spark, as i've tested with a spark tester and it matches the rest of the cylinders, plug to injector is fine. and the vacuum is when i hold it at 2500, initially is spikes to 22 and returns to 18 (normal operation).

 

So it does not return to 18" while holding the throttle at 2500rpm correct? It stays at 22" right?

 

it does return to 18. in a nutshell of what i've established. Spark good, vacuum good, compression good, fuel pressure good, map sensor good

 

How old are the cap/rotor/wires/plugs? If you replaced to O2 sensor, what brand? If you didn't replace it, unplug it, and see if the truck runs any better.

 

Guys... he said he verified good spark with a spark tester..... how does the plug look? wet / black ?

 

just replaced plugs with recomened champion plugs with correct gaping, #8 plug is golden brown, and all the others are white, let me remind you truck had plenty of power before the plenum fix, so its something on the top end that was removed eliminates 02, heads, compression, and everything else that is not related to intake removal. just some info about me, im not a DIY i'm at a top notch automotive college in NYS (job posting from all over the nation) techs leaving this school are making 100K+ i spend 4 hours a day in lab working on real vehicles, this happens to be my vehicle. im currently a freshmen so i haven't gotten into deep engine performance yet but i know what to look for when diagnosing engine problems. so its not going to be the small stuff such as a tune up. i'm thinking inectors, but the senior automotive engine performance class professor thinks its vacuum. i want to fix the problem myself because they have such a big customer base they are backed up for 3 weeks before they can get it in and school ends in 4 and they still need to put 4.10 gears in the dana 44 front end.

 

It ran fine before the repair, and runs crappy afterward, probably not going to be an injector thing, unless the clip for the number 8 injector isn't holding on tight, and giving you a miss......