Talked with my dad tonight. He's been working on my G at the shop(I'm at college). He was testing the FPR tonight. He was following what our Hayne's manual said. He disconnected the return line and capped it. He then energized the pump to build pressure, and then checked the rail pressure. It was like 70+ psi! The manual said 35-39 was ok and below that meant bad pump(already replaced), but ABOVE that meant BAD fuel press. reg. Well, I have a Holley AFPR sitting there so we're gonna replace it and the O2 sensor. Hopefully this solves all the problems I've been having. **Also, after this test, it said to un-cap the return line and put a hose into a bucket. He did this and energized it again and it showed like 48psi or so! Once again, it said that it shouldn't be above the 35-39 mark. This was all with the motor off and just fuel pump pressure applied with vacuum line attached. I HOPE THIS FIXES IT! We're thinking it will. Later I'll let ya all know if/when this fixes it. THANKS FOR ALL THE HELP EVERYONE'S THROWN IN!

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'91 GTA:
www.fbody.com/members/91WS6GTA

 

GTA,

Not to burst you bubble, but the stock setting for fuel pressure is 37 PSIG ± 3 PSIG with the engine at idle and the vacuum line connected to the FPR. Disconnecting the vacuum line (or testing with no vacuum - like not running) will raise the pressure 5-6 PSIG. The 48 PSIG is not excessively high, or at least not so much so that the car wouldn't run correctly.

The return hose dumping fuel to an open container only means the pump can flow enough to make pressure and return fuel to the tank, The real test should be to allow the pump pressure line to fill an open container for fifteen seconds. If the pump will deliver at leat one pint of fuel in that time, it is O.K. The FPR really should be tested for spec pressure at the Schrader valve on the right fuel rail with the engine running. 34-40 PSI is acceptable.

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Later,
Vader
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"I'm'a do Things My Way - It's My way or the Highway."
Adobe Acrobat Reader

 

Vader-
Hey, thanks for the reply. I don't want to insult you or anything... I know you're very smart on this stuff, but why is it 70psi then? I can't see how its possible to have 70psi on the rails with a 40psi regulator. It shouldn't let that much pressure go thru... regardless of whether or not the motor's running? Do you have any other ideas on whats wrong with the car? Thanks for any help... I just hope you're wrong for my sake! haha

*Also, why then does the Hayne's book say to do it this way to rule out the FPR?? Just curious... I know books aren't always right, but we've had good luck with this basic book quite a few times. Thanks again

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'91 GTA:
www.fbody.com/members/91WS6GTA

[This message has been edited by GTA91 (edited March 12, 2001).]

 

He disconnected the return line and capped it.

the pump was deadheaded..
that's why it made 70psi.
sounds fine to me.

 

No offense, but those Hayne Manuals aren't worth the paper to wipe your butt.

Vader has described the proper procedure for testing the fuel pressure.

BTW, you don't list any of your modifications (if any). Some will make your engine run richer unless you compensate within the eprom. FYI, the stock GM eprom is designed to run too rich. I ended up pulling 15-20% of the fuel away at the stock Fuel Pressure. Then, because I like the better atomization of higher fuel pressure, I had to pull somemore out of the higher load ranger of the Volumetric Efficiency Tables (the table in the eprom that controls fuel deliever on a Speeed Density car).

 

OK... once again, not wanting to offend anyone, but isn't the return line off the regulator or what? If so, the cap shouldn't matter and the regulator still shouldn't let that much fuel go by?

*This kind of makes me mad in a way. I've asked for help for the past month, and I don't think any of you helped me. I know a few of you are probably the smartest guys on this board too! I just want some help, so can you help me noqw if this isn't the problem? I doin't mind a little bashing on me, but I need some help to compensate. THANKS GUYS!

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'91 GTA:
www.fbody.com/members/91WS6GTA

 

Vader and ODB are right, as usual. GTA91, before you put a new regulator in make sure you follow the right procedure first as follows:

Connect a fuel pressure gauge to the schraeder valve on the fuel rail and DO NOT disconnect anything (return lines, vacuum line, etc.). Now turn the ignition key to the ON position and listen for the fuel pump to prime. You should record a pressure between 43.5 and 48psi. Now start the engine and it should fall to 35-40psi. Shut it off, turn the ignition key to the ON position again for 3 seconds or so, and back off, and just sit there and watch how long it takes for the pressure to bleed off. Mine didn't lose more than 1psi in 20 minutes.

People are trying to help you, but you gotta do what they say and not make up something that is way outta line with standard procedures .

 

Thanks, but why are you saying I'm making up a procedure? This is whats stated in the manual. Gees, its like you think I just made this up off the top of my head. I'll talk to my dad and see what he says Later.

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'91 GTA:
www.fbody.com/members/91WS6GTA

 

From your description, the procedures for both fuel FLOW and fuel PRESSURE tests were intermixed. See section 4B-3 of the Haynes manual, where the feed line (not the return) is disconnected for a fuel flow test, and neither is disconnected for a fuel pressure test. The two procedures are very much separate undertakings. Helm and Chilton's confirm. Go over it more closely with your dad since he may have not told you exactly what he did, you may have mistaken what he said, or he may have followed the incorrect procedure. More than likely it's just a miscommunication between the two of you. No flames intended at all, I just wanna make sure you test it right before you go to the trouble of replacing it .

 

OK then. Thanks! I'll check with him. Either way I want to replace it with my Holley AFPR. I'm sure he read it correctly though... I know he said he did like 3 times to make sure he was doing it right. he's also pretty smart about stuff so I hoping he's figured something out. Talk to you later.

**Sorry if I sounded like an *** , but this stuff is very frustrating sometimes

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'91 GTA:
www.fbody.com/members/91WS6GTA

 

GTA, not to be a bad guy, but 1) we don't get around to answering EVERY question ALL the time and 2) this is well documented in many places at www.thirdgen.org . Did you try "searching" through the boards or archives on the proper way to measure fuel pressure?

It is kind of disenheartening for many of us guys who see the same question asked a million times, when people just have to do a "search" and often find more information that they could ever imagine.

So, please before you start getting angry at people, ask yourself what you have done (besides posting a question) to research this problem.

I STILL do searches on through the archives and posts before I EVER ask a question. That is probably why I generally never ask a question...someone generally asked it a long time ago. About the only thing I cannot find any answers on is regarding Assembly Language Programming on the eprom.

 

I have searched b4 and that wasn't the case this time. We tried testing pressure that way and saw that the manual said to do it this way also... to isolate the regulator. No big deal... just wanted a few ways to check.


*This was NOT a post that had previously been posted b4 either. This was mine, and I tried to read any other posts around similarto see whats going on. I tried everything else 1st. Nothing helped! I am still clueless. I think it may possibly be the HEI module or pickup in the distributor. We tried a AFPR and o2 and still no luck. We hooked up a scanner and we're not sure exactly what to look for. Looked at MAp and TPS and other readouts but can't find anything. Any ideas on what to look at?

*Thats fine you guys don't have time to read all my other posts... I understand that! I was just a little upset becuz I can't find enought help and info to fix it. I'm not blaming anyone, I just need some help on this one... BADLY! Later

Thanks for the concern!

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'91 GTA:
www.fbody.com/members/91WS6GTA

 

GTA91 - You done a cylinder balance test yet? Just curious since my car runs like a$$ and I did one just the other day. Turns out 4 or 5 of my injectors may as well be disconnected. Clogged injectors could be your problem too, just an idea.

 

When you capped the return line, then energized the pump, the return line couldn't bleed off any pressure since it was capped. The pump is running and there is no place for the fuel to go except to make more pressure in the entire supply line, thats why you saw the 70+ psi.
I described the proper procedure before for the regulator, leaky injector, and pump check valve. Engergize pump first, after it shuts off, if your losing pressure, clamp the rubber part of the return line off, if pressure stops dropping, then bad regulator.
*
But it doesn't sound like your problem since it still happens after changing reg.

 

Thanks guys for the replies. With all this help, I'm bound and determined to FIX it! Its sad... I have my T56 with all the stuff sitting there ready to BOLT in, but we can't/won't until its running right!

JETHRO-***Anyways, how do I do a cylinder balance test or whatever?

2KWIK6-**I'm wondering about the injectors though. I tested them with an ohmeter and ok... I'm assuming they're not leaky becuz it held awesome rail pressure for long amount of time. Is that right? Also, my car is using a little oil(145k miles) and I noticed yesterday that the plenum had a little extra oil/carbon/grime buildup. Could this be clogging my injectors? What type of cleaner should I run or use on it in it?

BTW- Doesn't GM make some kind of stuff(spray) that you unhook your airpump and spray the SH#@ out of your TB and then go run the SH@! out of your car. I was told by a fellow 3rd gen'r that he had to do this to his GTA about once a year to keep the upper end clean.

*1 last thing... could a faulty(shorting) HEI module or pickup coil cause severe "bucking" and shuddering like this. They're cheap and thought about maybe replacing to.
THANKS AGAIN!!!

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'91 GTA:
www.fbody.com/members/91WS6GTA

 

GTA91 - To do the cylinder balance test, start the car and once the idle steadies disconnect the IAC and block the throttle plates slightly open with a piece of cardboard or something like that until the car is idling steady at about 1,000RPM. Now go down each side of the engine and disconnect each injector one at a time and listen for an RPM drop. Plug them back in before you go to the next one so you only have one unplugged at a time. Each injector should cause the idle to drop the same amount as the others when disconnected, and those that only cause a slight idle drop or none at all indicate a dead or weak cylinder. If your ignition system is new like mine, this would indicate faulty injectors. All of mine tested good for resistance and no leakdown, but many of them didn't do so hot on the cylinder balance test so they are clogged or don't have the proper spray pattern.

A faulty pickup coil can cause some driveability problems but ignition modules usually just crap out altogether. I have replaced both in mine and it didn't make a difference, so your best bet is to do the balance test first and then see where to go from there. Hope this helps.

 

One more thing, when you block the plates open do it at the minimum air set screw, just stick something between the screw and the lever to open the blades a little. You probably know that but I just wanted to make sure.

 

Ok, then! We've done one of those b4 I just wasn't sure what you call it. I'll try it though. I guess you have to unplug the IAC to keep it from "messing" with the idle when you unplug them? Well we'll give that a shot.

**Also, I heard that those modules just go out, but a guy we know had problems like this and that was the only thing that fixed it!

I'll tell my dad to check them and we'll go from there. THANKS

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'91 GTA:
www.fbody.com/members/91WS6GTA

 

Vader,
You said disconnecting the vaccuum line would make it jump to 48 psi? Would that help a TPI car pick up a couple of tenths at the track?

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1980 Camaro, '88 Police 350 engine, Headers, full exhaust, completely redone, my baby!
1988 Iroc-Z L98, MSD 6a, Accel coil, K+N's, Airfoil, Coolant Bypass, Flowmaster, Gears, Late model Bose, I like the 80 better

 

Yep, if its holding rail pressure for a long time without any lines clamped shut, then you have no leaky injectors, and a leaky injector wouldn't cause running problems at high rpms anyway since they're open almost 100% anyway at WOT.
When a coil goes south on my GN it sputters and pops during light to moderate acell, but thats because it has a coil per pair of cylinders, 3 total, so when one goes, I've got 4 cylinders still getting good fire with the direct ignition. On a TPI car with electronic distributor, that probably would not happen, never had one go out on my TPI before.