just got done with a fuel presure test. with it running 39psi. then i shut it off, dropped to 22psi- staying there for 10 minutes, dropped to 20psi- staying there for another 10 miuntes, dropped to 18psi- staying another 10 minutes and i quit there. so by the book 39 psi is right on the money. i now see why people take the vaccum line off the FPR, i did it during the test and the fuel pressure went to 44psi.
than i checked most of the vacuum ports and got by my gauge in the normal, green which is betwwen 18 and 22 inch Hg.
but shes still idleing kind of crappy?????
when i got the vette 4 moths ago, it had a whole new exhaust system put on, not sure about O2 sensor so thats on the way. i changed the plugs, cap, rotor, remove TB and cleaned it, clean IAC, re-set TPS and low idle like the GM manual said. it failed a emissions test at a idle for high hydrocarbons. i did another code scan and nothing is showing up but the code 12 the system is working.
any idea were to check next. bad wires?

 

Your fuel pressure is dropping too fast after shut off....hook up the gauge and start the car and watch the pressure...rev the engine by hand and see what it does.Check the injectors ohms hot and cold with a digital voltmeter as well.

 

i don't know if it will help or not, but my 93 would idle rough just every once in awhile. when it did idle rough it would die unless i gas it alittle. my problem was the throttle body was dirty or carboned up.

 

What year Vette?? It sounds like an early an L98.

Use the ECM's Field Test mode, described on my site, to see if it's going into and staying in closed loop.

If it's missing at idle clip a timing light onto each plug wire to see if misses coincide with missed flashes on a wire.

To test for a fuel system leak, just turn the key on for a few seconds and record the pressure changes vs time. It should hold very close to that 44 psi value for a few minutes, with a slow drop off.

 

yes i have 1986 L98 Vette.
so i should have high fuel presure then 44psi while its running? how long should it hold presure after shut off? right now it goes from 39psi running to 22psi right at shut off almost right away. then each drop of psi to about 16psi is each about 10 minutes apart.
ohm check the injectors, i hope thats in the service manual?
i did do a code scan again with my code reader, and only getting the code 12. isn't that telling me the ECM is working o.k.?? i will do it again to check the speed of the 12 flashes.
i have been running fuel injector cleaner and its not doing the long start when warm deal either, not that it did it alot at first.
i have a new O2 sensor coming, and i have a cooant temp senosr ready to go in, i am going to do them and see what hapens too. and recheck with my fuel pressure tester. why dose the book say 34psi to 39psi is right if it should be 44psi. now when i disconnected the vacuum line to the FPR i got 44psi. i am still wondering if i missing some thing with all the vacuum lines or not have them right??? last owner had most of them disconnected, like nothing going to the FPR.. the sticker on the rad it kind of hard to read on my 86. and body got some good pictures of the aft right intake and how the egr is suppose to be hooked up!!
thanks guys!!!
my aux fan comes on when the dash gauge reads 170 temp wise, could that be making the engine run to cold? last night i was driving around town temp was reading 168, only a cool night here in maryland.

 

the vacuum line coming out of the fuel pressure regulator, not usre i have this right, but it T's off to the forward vacuum port on the intake pelnum and the other end goes into the air divter system. EGR value vacuum line runs under the pelnum to the EGR silniod, other line coming out that foes to the vacuum port coming out of the throttle body. i am just going by my faded sticker on the radiator. not sure if theres any divert values in any of these lines, most of the vac lines were missing or disconnected when i got her for my own.
any pictures would be great!!

 

From what you are reporting, it sounds as though your running fuel pressure is right on th money. As you open the throttle, the vacuum drops. At WOT the vacuum is virtually zero and the fuel pressure is at it's highest, as it should be for full throttle. It does seem, as mentioned, that the fuel pressure bleeds off a little too quickly when shut down. Try pinching off the supply and return lines to diagnose the cause.

High CO2 indicates a rich mixture. Look for vacuum leaks. If air is entering either the intake or the exhaust system, it could cause the O2 sensor to read lean, making the ECM add fuel to correct the problem. Another test would be to pull the vacuum hose off of the EGR valve, plug it, and observe the idle quality.

I hate to see you throwing money at it by replacing the O2 and the CTS, without them having tested as failed.

RACE ON!!!

 

cfi
if my fuel pressure is 39psi at a idle what should it jump too when i hit the throttle??
i am still not sure i have vacuum line hooked up right??

 

There's some procedures in this tech tip that should help you in diagnosing any possible fuel system problems or eliminate them as a cause.
https://www.corvetteforum.com/techti...=192&TopicID=2

 

got a PCV question, last owner put on some chrome Edlebrock value covers, driver side has the PCV in it. the right side has a air breather in it, would that breather be defeting the PCV system any?

 

There are two vacuum ports on the rear of the plenum, use either one for the FPR.

You should make fuel pressure measurements with the vacuum line disconnected from the FPR and plugged.

If pressure is dropping immediately by 10psi or so, you have a fuel system leak. Removing the gas cap door & rubber boot and clamp the feed & return lines in turn and power the fuel pump:
-If pressure does not drop with the feed line clamped the problem is with the check valve in the pump.
-If pressure does not drop with the return line clamped the problem is with the FPR.
-If pressure drops with both lines clamped the problem is with a leaking injector; you should pull the set (all 9) and send them to Rich at Cruzinpeformance (link on my site) for cleaning, flow testing and leak testing.

If you would like a pic of vacuum tube routing schematic send me an e-mail at jgkov@msn.com and I'll return the pic.

 

i have been smelling gas in the back of the car snce i have had it, i changed the gasket around the fuel pump mounting area, cut return and feed lines a little shorter so to get a good peice of rubber under the clamp area. found a bad return rubber line last weeks under the drivers seat area under the car. today i took the spare tire out and carrier to get a good look at more lines. some metal lines a pretty rusty, and i am going to change all the 1/4 rubber fuel lines i can get to. i have a new to me fuel sending unit from a vette in AZ with no rust, mine was really bad!! Maryland uses road salt! beofre i put thia sending unit in i replaced the fuel pump and wiring and sock. i am wondering if i am looseing pressure from the bolts on the mounting flange or something? but even after all that still no change so i still haven't found the problem yet??
the FPR vacuum lines was plugged off when i got the vette, i wonder if that was to hide the fact he knew it was bad? because i did check the FP with that plugged and it went to 44psi from the 39psi i was getting.

 

Don't test it by hitting the throttle. Just disconnect the vacuum hose as you have. Generally, the fuel pressure should jump by 10 psi when the vaccum is disconnected. 39# to 44# may be OK. Check to be sure the diaphrgm in the FPR isn't leaking.

Your PCV system sounds good as far as you've explained it. You need a filtered inlet, the breather(?), and a vacuum source hooked up to the PCV valve in the opposite valve cover, exhausting the crankcase fumes to the inlet system so they can be burned with the air fuel mixture.

RACE ON!!!

 

I saw about a 6 psi increase pulling the line off the regulator.

 

should my PCV only have one vacuum hose coming out of it like a L shape or should it have two lines and make a T shape?
any body with pictures of the right and left side of engine value covers and vacuum lines?

 

any body got any digital pictures of there PCV and EGR hooked up the right way the can send me. i still think i don't have them right or missing parts, like values and other deals.

 

For a proper and effective crank case vent system, you don't need a tee. My car has one, stock. The third leg of the tee runs up front to the vacuum reservoir. When you start deviating from stock, it is wise to know EXACTLY what you're doing, and why.

RACE ON!!!

 

well thats just it, i am not sure what stock is.

 

It sounds as though you could get a lot out of a FSM.

RACE ON!!!

 

i have a 1986 GM service manual, but i can't find any thing on the vacuum lines and other parts to it. what page?