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Vacuum line at FPR

Paddywhack

Well-known member
Joined
Aug 15, 2008
Messages
157
Location
Forestdale, RI
Corvette
1986 Dark red coupe
Now with most of the plumbing from the AIR system removed, what do I do for a vacuum line at the FPR? Also, did a leak test on the fuel system and it dropped from 36 to almost zero in a few seconds. Time for new injectors? WAS going to call FIC, just havent had the chance yet. Car is bucking at low speed and having trouble maintaining an idle. 1986 L98, bored .060, lunati cam, long tube heders, custom Harris Stage II chip, no egr, true duals, no cat. :puke
 
Just because the FP dropped doesn't mean it was caused by leaking injectors. There is a check ball in fuel pump that can leak as well. Also, a defective FPR could cause this. Do you have the factory service manual? There is a procedure to isolate the drop. When my 88 injectors were leaking pretty bad then did not drop from 40 to 0 PSI in seconds. The pressure was not holding steady as they should. I'm a fan of Bosch IIIs, but I hate to see you replace them and have the same issue. If I remember correctly the FPR vacuum line attaches to the plenum.
 
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Diagram


Toptech,

I have one hose coming out of the solenoid that goes nowhere. One coming out of the bottom and tees off and neither hose connects to anything. I have a 90.


Is this diagram correct for a 90?
 
Toptech,

I have one hose coming out of the solenoid that goes nowhere. One coming out of the bottom and tees off and neither hose connects to anything. I have a 90.


Is this diagram correct for a 90?

That diagram I believe is for an 86, only posted to show the FPR vacuum hose goes directly to manifold fitting. Did you check the radiator shroud on your 90? A vacuum diagram for all emission controls is usually on a sticker posted there. If not try posting some pictures and I'll see if I can help.:thumb
 
Diagram

That diagram I believe is for an 86, only posted to show the FPR vacuum hose goes directly to manifold fitting. Did you check the radiator shroud on your 90? A vacuum diagram for all emission controls is usually on a sticker posted there. If not try posting some pictures and I'll see if I can help.:thumb

Didn't mean to hijack the thread.

I Figured it out.

The bottom hose is a vent and the one in question goes to the purge solenoid which has two hoses going to it.

I have the bumper off and replaced the impact bar and skid bar. it just came off when I removed the turn signal lens.


getting ready to paint.


Thanks

Bob
 
Thanks guys, I have that diagram, but with the elimination of the EGR and AIR plumbing, can I just put a line from the plenum to the FPR? I do have a FSM, I didnt however look at the elimination procedure to isolate the drop in pressure. Will get on that tomorrow afternoon.
 
Thanks guys, I have that diagram, but with the elimination of the EGR and AIR plumbing, can I just put a line from the plenum to the FPR? I do have a FSM, I didnt however look at the elimination procedure to isolate the drop in pressure. Will get on that tomorrow afternoon.

Yes.
 
I put a line from the plenum to the FPR and it ran horrible, no throttle response, burpin and fartin'. Blocked off the FPR and plenum and it leveled off again, but still not enough to adjust the idle. Followed the FSM procedure for holding pressure, ie: pinching supply flex line, pinching return fuel line and has no difference in the pressure drop, down to zero with in seconds. Trying to get a hold of John at FIC now.
 
I would check your fuel pressure regulator. If you have a hand vacuum pump see if it will hold vacuum, if the diaphragm is bad you are pulling fuel directly into the plenum through the vacuum line.
 
checked the vacuum line for any fuel residue, no odor or wetness at all. Dont have a hand vacuum pump, will see if I can locate one though.
 
Its almost a sure thing that something is going on with the FPR, just hearing that connecting it made the engine burp and stumble makes me think that its leaking gas. If it had a leak it may not actually leak unless that vac was there...
I'd recheck FP and carefully read the gauge. Its very helpful and will tell you many things. You should get system pressure up just by turning the key to ON, not start,. and it should hold that pressure for a good 15 minutes.
After running it should hold for even longer.

Rapid pressure drop does not necessarily mean the injectors are leaking the fuel. The engine would flood like crazy if that were the case. I've have had that happen and the flooding is very very obvious.
 
results are the same with the engine warm or cold...key on, not start, pressure goes to 34 -35, key off pressure drops to zero in seconds. Fuel pump is new.
 
Just going through old posts trying to get ideas and I remembered when I replaced the fuel pump in January, there was no pulsator on the pump. Could this be involved any way?
 
i doubt it. I took mine out and it made no difference in anything. Some folks say that it helps keep the needle steady on the gauge...

IF the fuel was leaking past the injectors, the engine would be soooooo flooded that it could not fire and when it did, there would be black smoke everywhere. I have seen injector flooding. When the set leaks, they leak into the manifold and flood the intake with liquid gas.

With only key to :ON: there is no inj signal to open. So, at least some should hold their fuel. To dump all the static pressure in seconds, they would all have to be stuck wide open.
The pressure drop is coming from elsewhere. It has to be in the Regulator or flowing backward to the pump. There are no other mechanical parts to the system. The problem has to be in the reg or pump if pressure loss is happening.
 
Just because the FP dropped doesn't mean it was caused by leaking injectors. There is a check ball in fuel pump that can leak as well. Also, a defective FPR could cause this. Do you have the factory service manual? There is a procedure to isolate the drop. When my 88 injectors were leaking pretty bad then did not drop from 40 to 0 PSI in seconds. The pressure was not holding steady as they should. I'm a fan of Bosch IIIs, but I hate to see you replace them and have the same issue. If I remember correctly the FPR vacuum line attaches to the plenum.

The FIRST thing to have after purchasing a vette is FSM. The LAST thing to do to a vette is modifications which change baseline specification/parameters, UNLESS it was done on a NEW car, AND, the new baseline specs were put into a chip, AND were recorded on paper.

Otherwise, tune diags is a shot in the dark YUP...

You'll test pump strength and FPR diaphragm spring strength later, but first:

First, cap the return line, AFTER the FPR. DON'T PINCH LINES - you'll damage them, especially if you really pinch to STOP flow.

After disconnecting and capping the line, COLD motor, turn the key on to prime the pressure in the fuel rails. Have a pencil/paper ready (although you know already it's dropping almost immediately).

Note pressure let-off time in 5 second increments (or 10, 15, 30). If (since yours is going to 0 in a few seconds, this won't take long to find.

Pull the FPR vacuum line, and get a whiff. If the motor was cold, you might find gas in the vacuum line. This will indicate a ruptured diaphragm in the FPR. Ruptured diaphragm will make for hard hot restarts, among other things, poor mileage, etc.

Fix, and start over.

If pressure still drops quickly, look for leaks along the entire line, from tank to FPR.

Fix, and start over.

If pressure still drops quickly, your injectors might leak. Put your multimeter on them, and test for resistance. Uneven or low readings could indicate leaking injectors. Pull the rails (with injectors) carefully from the manifold, get a container under each injector, and prime the rails. Look for leakers, and replace if necessary.

A tip for BEFORE pulling - squirt some Armor-All into the injector port if there's any debris in them, and blow away excess, or hit it with the Shop-Vac. You don't want anything getting in the ports behind the injectors into the intake, or anything blocking the o-ring seal at re-asembly.

Re-assemble, and start over. Quick pressure drop now is a faulty pump assembly.

End of static fuel pressure diagnostics. Now do dynamic test, to test the diaphragm spring in the FPR (don't assume it's good, even if new).

BOOKMARK THIS POST UH HUH YUP

--------------------------------
The vacuum line to the FPR is for acceleration enrichment.

Proper function is confirmed on a dynamic pressure test. Increased rpm's (and vacuum to FPR) makes extra fuel available for enrichment. This test however is after static tests have been completed...
 
Just going through old posts trying to get ideas and I remembered when I replaced the fuel pump in January, there was no pulsator on the pump. Could this be involved any way?
I'd pull the pump and check it out!! If you can blow through the pump back-wards,the check valve is stuck open and will drain back into the tank in a heartbeat!!:thumb
Also,If you have a leak between the rubber line from the pump to the steel tank outlet line,fuel pressure will bypass in the tank and cause your symptoms!:thumb:thumb:thumb

PS. If it is a leaking FPR diaphragm bleeding Fuel Pressure that quick,believe me there would be plenty of fuel in the vacuum line to detect!! :D
 
I will try blowing back through the fuel pump tonight and checking the hose connections. Schrade, thanks for the technical input, but I just want to make a couple things clear, one of which you contradict yourself on...I do have a FSM, bought it shortly after buying the vette and joining here...the FSM says to PINCH the flex lines, I agree with you this doesnt sound the brightest, but it is in the FSM. I bought the vette already "modified", my goal was to get it back to a functioning sports car with a little kick! I knew the engine needed work when I bought it, what I didnt know was that someone changed the L98 and installed a 305. I was able to locate a 4 boilt main that needed cleaning up..hence the .060 over. By that time long tube headers were recommended in here for breathing and such and so installed, along with a mild cam (it was already apart and needed a cam), all this information was given to Harris Chips, again recommended in here, and they customed burned a chip and walked me through some installation issues over the phone. Great people there by the way. Then there was the frustration over water in the oil on the new engine, which came back out again..as recommended here, cleaned up, new bearings and back in she went...so you can see me patience level is waning..however being a thick headed Irishman, I am going to get this running perfect! with the help of the fine folks here, I think we are on our way to completing this task.
Sorry, had to rant about something. I thought about the injectors last night and it hit me, they were the same ones that were on the 305...so, spoke with FIC today and looks like I'm ordering design 3 injectors, 22 lb is plenty sufficient according to them. I will do all of the recommended testing on the FPR and pump, and keep posting results...again thanks to all for letting me vent!
 
...so you can see me patience level is waning..however being a thick headed Irishman, I am going to get this running perfect! with the help of the fine folks here, I think we are on our way to completing this task.
ALLLLLLL-----------RIGHT !!!!!!!
Another Irishman who doesn't know the meaning of quit when he gets something stuck in his head! When you get this beast fixed (and you WILL),
the smiles will be a long time on your face. Not to mention the beer after the repairs have been completed, as well as the stories about all of the problems you overcame, with of course, some Irish "embelishment" ! Seriously, my hat's off to you for deciding that you want this car to run "right" and doing what it takes to make it happen. I've seriously enjoyed reading these posts, and will keep on reading till it's RIGHT !
Andy :w
 
Pinch the lines will work, BUT, if the pressure doesn't THEN hold, you're not knowing if the fuel is getting by the pinch, or if it's gettin' by somewhere else. So all you can do then is tighten the pinch, and that's when you could cause damage.

With a cap, you KNOW where it AIN'T goin' if it DOES let off pressure...

My .02

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