hello guys and girl i have an 89 iroc-z 305-5spd.

the car has full bolt on other than roller rockers msd box and underdrives.

the factory owner replaced my injectors with 350 injectors (22*) and there is an afpr on it, no idea brand.

anyways the problem is it runs a little bit rough at idle. it realy seems like it's a vaccuumm leak but, ive searched and was left empty handed several times.

i've heard there is a vaccuum hose under the dash, that would cause if, if off or leaking that i can only use defrost, i have that problem but, where is this line located???

2) anyways biggest question, what should the factory pressure of an 89 be set at

3) should the vacuumm line to the afpr be disconnected while setting it or connected?

thanks for the info.

 

well i didn't get a super fast response so i just played with it a bit. Seems it was set at 48lbs line disconnected. Seemed awful high considering this is only a bolt on car and the injectors are already 22 lb hour as opposed to factory 19 lb hr.

i backed it down to 44 psi disconnected, not sure if thats necessarily correct but, it seems to rev a little slower but, not kneel over up top like it use to as easily.

i dunno the engine feels plenty peppy down low but, up top it's lacking
i finally pretty much topped it out after 6 months of owning it and it seems about all it's good for currently is 125 ish, i dunno exact speed because, i was off the speedo, i'm sure it would pull 130 but, it was definetly real slow going after 110 i know that.

maybe the high fp was just flooding it out, i know i got to 100 real easy down my back road after testing it a couple times. Seems like it usually struggles to hit 95 in the same space normally but, it could be the *** dyno lying to me, we'll c come spring time i suppose.

 

Whats the timing set at?

I have 24lb on my 305 and last time I checked, my fuel pressure was 48psi with the vac line off.

 

well thats probably all fine and good for your setup but, mine currently is stock heads cam and intake too big limiting factors for sure......

i dunno i think it's something i realy need to test n tune....

not sure what my timing is at realy need to invest in a light one of these days but, i just havent got around to it honestly.pretty sure it's most likely factory 6 btdc tho.

 

How open is your exhaust ? Are you running short or long tube headers ?

 

shortys,l edelbrock y-pipe, factory cat, borla 3 way adj. cat back.

3 in muffler 2.5s out with quad tips.....

mid pipe is only peice not mandrel bent as it was rotted out and needed replaced..

still would love to find out factory fuel pressure for an 89 tpi 5 305 car if any1 knows.

i'll probably go buy a timing light tonight and c where it's set at, probably run 8* and c where that gets me.

 

43.5. Adjust it with the vaccum off.

 

And idling.

 

great so i'm pretty much dead on i'd say i'm still running high though as my injectors are 22# not 19# but, for now it feel like it's running well, i'll probably drop it down to 40 in that case and c if it affects me negatively in anyway.

didn't get a chance to get a timing light, have been sick all weekend and had to work + my dad wanted me to put an exhaust on his truck..... so yah story of my weekend.

 

Well, I think part of the problem is you're looking for gobs of power in a 305 TPI motor.

Low-end is what TPI is about, it's not quite the best up top.

Not to mention - a 305 is not going to have the power a 350 or something bigger has.

 

naaaa i know quite well what the car is capable of and it's short comings i am just trying to get it to run smoother currently.....

previous owner wasnt the smartest in the world, he put 22# injectors in it with factory prom settings as far i know...... That plus he had the pressure about 5lbs to high, when you combine those 2 it runs quite rich.

i'm pretty sure it was way rich up top...... i almost never go over 100 but, the 1 time i topped it out it realy realy felt lacking in the 4,000 (yes i know tpi dies on the little 305 before 5k but, it wasn't that). category. I know it was running pig rich so i'd expect lowering it down will help. Maybe i'll try and wring it out again if i have a late night down a deserted highway anytime soon but, doubtful....

don't get me wrong it's healthy but, i could do better is all i'm sayin.... Nothing wrong with making improvements in hp/economy/longevity for free!

Btw 305 5 spd cars are damn near dead even with l98 auto cars, your talking the difference of a couple tenths if that!

Hell i can stay right on my buddys old 97 lt1 camaro until about 80 then its all tailights. Usually he's a couple cars ahead by the time i'm 80 but, not bad for a bolt on puny 305. Then again he runs an auto also.

not saying a 305 is top dog or nothing (no replacement for displacement) but, it's respectably fast enough that i don't i should be running out of steam at around 110 is all.....

o i forgot does any1 know anything about the very first question? I still realy realy think theres a vaccum leak and none of the intake gaskets are, the boosters not and i realy can't find any underhood lines that are either....

1.) i've heard there is a vaccuum hose under the dash, that if off or leaking could cause me to only be able to use defrost, i have that problem but, where is this line located??? What i mean is i can't use my upper or lower vents. Is this maybe a vaccum operated flapper door or does this even pertain to my 89, don't realy know anything about hvac....

 

The vacuum line in question will hook to the back of the HVAC controls, in the dash. Pull the control head, and check the lines there first, if the problem is not right there, just follow them back. GM used plastic tubing for the vacuum lines, and as it ages, it tends to get dry, and brittle. Breaks WAY too easy.....

Also, keep in mind that past 100 miles an hour, there is a great deal of wind resistance to overcome, to go much faster. Your 305 is getting close to the point where the TPI falls flat on it's face. You could try some home porting work to clean up the plenum, and see if that gets ya any faster. Only money involved would be some gaskets, and the tool to do it. Dremel works pretty good.

 

awesome yah i'll check behind the hvac panel thing. I'm wishing my self luck considering thats my last hope for this vaccum leak like problem.

yah i'll be porting it while it's off and semi siameseing the base along with throwing a set of ported 416s on it and a crane 2032 powermax cam, so i hope i'll be able to get me to a 5,500 rpm pull.