garyc4

Ok, making great progress bringing my 84 back to life. After rebuilding the TB's, installing an 85 fuel pump along with new sending unit, replacing all rubber sections of the fuel and return lines, flushing the lines with carb cleaner, converting to adjustable regulator, and installing the fuel pressure guage, we started the car today and it fired up nicely.

Now the question: initially when it fired the fuel pressure read 8-9 psi. good place to start. I then began adjusting the fuel pressure while the car was running and saw the pressure slowly rise. BUT, at about 12 psi, I ran out of adjustment. I visually checked the tab that sticks out of the regulator housing and it was all the way at the top of the slot. No room to go higher. This is not what I expected.

Anyone have experience with this and can offer any observations or advice?

Also, we noticed that the front injector had a nice spray pattern, but the rear injector had a poor pattern, and after several minutes began dripping instead of spraying and was obviously restricted. I'll remove that injector and try cleaning again. Any suggestions on home cleaning remedies appreciated as well. Thanks!

knikula

how are you reading the pressure? I need to check that on my crossfire as well...

to clean my injectors, I took 15 psi of air pressure, connected it to the outlet of the injector (so blowing opposite to the direction of fuel flow), and immersed the injector into a coffee can full of water... you could see air bubbles escaping as the injector was leaking. Then put 12 volts across the terminals to open the injector a few times while it was under water...seemed to work, as the injectors spray fine now, and don't leak after I shut the car off.

Not saying this the right way to do this, but it worked for me...

corvettenorway

https://www.corvetteforum.com/g/picture/1347319 this is my fuel pressure meter....https://www.corvetteforum.com/g/picture/1347330 this is the stock pressure regulator ...

corvettenorway

bad spring maybe ? have you cange the fuel filter under the car ?

garyc4

Pressure reading comes from a replacement line between the TB's which incorporates as VDO pressure gauge. This was a kit that Crossfireinjection.net used to sell, before they folded. I bought it a while ago and installed it over the weekend. They also used to sell a tool that could be used on the stock regulator housing to adjust fuel pressure once the plug is removed from the bottom of the housing. Its a shame no one has been able to continue to make and sell these items.

One other note: I'm no expert, but I've read that 12 volts to the injector can damage it, and I've seen/read a bunch of guys use a 9 volt battery instead, and not keep the leads connected for too long, to protect the internals of the injector.

Thanks for your suggestions, I'll try your trick with the compressed air and opening the injector.

garyc4

Yes, changed the filter. I agree with you, seems like it could be a weak spring. Looking at how the regulator works, it seems that increasing the spring pressure on the diaphragm from below is what increases the pressure. So if that's true, then a stronger spring should hopefully lead to higher pressure. But as I've said before, I'm no expert.

I saw some higher pressure rated springs, I'm gonna try that next unless some other advice comes my way that makes more sense.

corvettenorway

i got the stock spring , and are running 15 psi pressure from that read this https://www.corvetteforum.com/forums...-82-vette.html

garyc4

Yes, I understand others have also. Which is why I'm surprised at my results yesterday.

Can you tell me about where the tab was located top to bottom, in the slot in the regulator housing? It would be interesting to know.

So for possible causes, I've got 1) inaccurate gauge, 2) malfunctioning brand new fuel pump, or 3) weak regulator spring.

Easiest to try would be regulator spring. Anything I try means just buying more stuff, and the spring is the cheapest. Thoughts welcome.

garyc4

Yes, that's an interesting and informative thread, thanks! I've got a stronger spring coming, so we'll see. Also will clean the rear injector at same time, as its not spraying properly.

Thanks again.

JoBy

If you have a rubber hose on the return after the regulator you can use a pair of pliers to pinch the hose. That way you can see that the pressure instantly increase. With the 1985 fuel pump you should be able to get well over 50 psi.

James84vette

Here is where I get confused. You said with an '85 fuel pump you should be 50 psi but yet I've read you should set an '85 fuel pump to 15 psi. Am I reading this wrong?

JoBy

No problem

You have to look at the complete system.

Tank -> Pump -> Filter -> Injectors -> Regulator -> Tank

The fuel pump create a flow.
The regulator restricts flow back to the tank to build pressure.

Without restriction you get maximum flow from the pump.
With no flow ( like pinching a fuel hose ) you get whatever pressure the pump is able to create.

Normal working pressure for the 1985 fuel pump is about 45 psi, but it is able to create a higher pressure than that. That is why I said that you should be able to get well over 50 psi from the 1985 fuel pump if you pinch a fuel return hose after the pressure meter.

The fuel pressure regulator is nothing more than a 'controlled' pinch. It restricts the flow exactly enough to get the desired pressure, 15 psi in your case.

The test with pinching the return hose is just to verify that the regulator is the problem. If you pinch the line and instantly see the pressure raise well over desired, then you know that the regulator is the problem.

garyc4

In a couple days the rear TB will go back together, with the injector I'm trying to clean and with a stronger regulator spring. I'll try the pinch test for sure, just to see what new fuel pump is doing.

Also have not yet checked/set throttle position sensor, so will do that also.

Thanks.

Buccaneer

Hello, we are still around really. If you rebuilt the TBs, did you mix the springs up by chance, they are different. You should be more than able to get 13psi from that setup for sure. 13 is all you really need for a stock CF motor to run well. If you maxed out the tab in the TB tower to the top and still can not achieve 13psi, something is wrong for sure.

One more thing, there are more than one rebuild kit for TBs, they are not all created equal. Some of the newer ones have the wrong bladder assembly and you will have pressure issues, this may be one of them.

Use only the GP Sorensen/Throttle Body Rebuild Kit (TBI) can order at (AutoZone)
For your 82/84 Chevrolet Corvette 5.7L TBI 8cyl, Part Number: 96-629, Price: $44.99. Price may have changed. Good luck

James84vette

Was suppose to have my fuel pressure adjusted today but the auto parts place around here had order and sent the wrong throttle body gasket. My mechanic ordered it form a vette parts place in the US, I forget the name. He should have it next week. Got the new fan/temp switch in so the fan turns on now.

garyc4

Thanks, good question. I rebuilt them one at a time because I didn't trust myself not to mix things up, but there's no doubt something's amiss because the tab is right up against the top of the slot with 12 psi reading and an 85 pump installed.

I bought the rebuild kit a few years back so I'm not sure where I got it, but I sort of remember getting advice from one of the two gents I was talking to at DCS before ordering. I might just order another one from the source you suggest, and do it again now that I understand how to do it.

I'll wait though, until I see what the new spring does that I already ordered, try the return tube pinch test, set the TPS, and get a clean injector in there (although the injector should have no bearing on my pressure issue). I'll use that as a new baseline and go from there.

This is all just a prelim to get the car running, I've got a renegade standing by for install next once the engine is back alive.

This whole project stalled a few years ago, but finally have the opportunity to re-engage, and its a lot of fun. I've done brake system, fuel system, exhaust system, and a bunch of cleaning. Now the engine....

It'll be a couple days but I'll report the result in case anyone is interested.

Tom400CFI

If you back the screw to lower the tab off the top...does your pressure decrease immediately? If so, then the spring is wrong/swapped (like Buccaneer suggested) or worn out (unlikely).

If pressure doesn't start dropping immediately, as you lower the tab, then your pump is maxed out, for some reason, or the hose between the pump/sending unit in the tank is leaking. Or something like that.

garyc4

Well I do know that the Berryman cleaning solution took the color off the springs. The only color I remember was the front TB spring, which was blue before the chem bath. NOt sure I could tell them apart at this point.

The pressure decreases pretty uniformly as spring tab backs down. As I mentioned before, the range has been about 8-9 halfway up the slot, and 12 at the top. I agree that it doesn't seem logical that the spring would just be "worn out".

I guess I could swap out the springs just in case I somehow switched them. Its not much work, and the new spring I ordered isn't here yet. Thanks.

Tom400CFI

Yes, I think switching springs is a good idea. Props to Bucc for thinking about that.

IIRC, "about 1/2 way" for my tab would have resulted in ~12 PSI or so. One time I cranked it all the way and got ~18 PSI. Car ran rich (black smoke, even).

Buccaneer

Thanks Tom. I do have some springs in stock and I can just send you one and see if it fixes the issue. Also, normally, but not always the rear spring color is red, but I have seen pink and blue and the comp side is usually green... again, not always. On the rebuild kits, the issue with the ones that do not work correctly (bladder wise) is the top swivel is not the correct shape or size. It will cause pressure issues and we have run across this in the past. The vendor we got the kits from swears they are OK, they are not and proven several times they do not work. The GP Sorensen kit is the only kit we/I ever buy now. Please post up what you find.