[Anthony Dale Enloe]

Need help SV gang. Car cut out several times then died. Let car set for several hours, it started right up. Next AM car started & I decided to drive it down to the corner store (wrong choice) without checking for codes. Car towed home as it refused all efforts to start plus the car horn decided to join in while trying to get it start? Checked codes & got DTC 16 & 36. Had just replaced the Opti and Coil so I started checking connection. DTC 16 was cleared by disconnecting - connect harnish from Opti to PCM. Car start but DTC 36 remained. Removed Coil/ICM and took ICM to Advance to test. Tested good. Reinstalled & car started up & no codes. "O" happy days. Next AM car cranked but wouldn't start. While checking for codes both the AirPump & Fuel Pump was cycling on and off while key was in the on position ? No DTC codes showed?? What is going on!! Thks for help or advise.

 

[crossflag]

sounds like a bad opti.again, Those are the same symtoms. But dont throw parts at it untill your sure.

 

[awnuts]

I need to replace my Opti also And have been reading and reading and found the only one opti that has a near 100% working is an OEM GM opti.
Yes that sucker aint cheap but its not a part you buy everyday. The MSD ones supposed to be better because it has an adjustment screw to adjust timing.Umm I thought the ECM did that.I do know when I get mine i'm going to replace the water pump too because of the weep hole and if its dripping there its going to screw up the new opti.The next year optisparks were improved with better venting. And I know someone did a vacumm mod to the 94 opti to suck moisture out. Good luck and I do feel your pain.

 

[vetteoz]

car cranked but wouldn't start.

http://www.mainstreamtopics.com/forums/topic/78-lt1-no-start-diagnostic/

 

[crossflag]

http://www.mainstreamtopics.com/forums/topic/78-lt1-no-start-diagnostic/

Great info, saved that link for myself...

 

[toobroketoretire]

Need help SV gang. Car cut out several times then died. Let car set for several hours, it started right up. Next AM car started & I decided to drive it down to the corner store (wrong choice) without checking for codes. Car towed home as it refused all efforts to start plus the car horn decided to join in while trying to get it start? Checked codes & got DTC 16 & 36. Had just replaced the Opti and Coil so I started checking connection. DTC 16 was cleared by disconnecting - connect harnish from Opti to PCM. Car start but DTC 36 remained. Removed Coil/ICM and took ICM to Advance to test. Tested good. Reinstalled & car started up & no codes. "O" happy days. Next AM car cranked but wouldn't start. While checking for codes both the AirPump & Fuel Pump was cycling on and off while key was in the on position ? No DTC codes showed?? What is going on!! Thks for help or advise.

I suggest attaching a hose to your fuel manifold with pressure gauge on the end of it then tape the gauge to your windshield. Then when trouble happens you can at least see if you have adequate pressure when you're cranking it. Is your fuel filter good? Just because you can hear your fuel pump running doesn't mean enough fuel is getting to your engine. The lack of fuel pressure probably isn't your problem but at least you can eliminate it as being a possibility.

 

[Slicktop]

I suggest attaching a hose to your fuel manifold with pressure gauge on the end of it then tape the gauge to your windshield. Then when trouble happens you can at least see if you have adequate pressure when you're cranking it. Is your fuel filter good? Just because you can hear your fuel pump running doesn't mean enough fuel is getting to your engine. The lack of fuel pressure probably isn't your problem but at least you can eliminate it as being a possibility.

That is a dangerous idea, LT1 C4 fuel pressure is 41 to 47 psi and it would not be smart to pipe fuel under that type of pressure up to the windshield and ****pit area and then drive arround like that. If you need to check fuel pressure do it safely with a test gauge at the fuel rail and the car stationary.

 

[vetteoz]

That is a dangerous idea
If you need to check fuel pressure do it safely with a test gauge at the fuel rail and the car stationary.

Is the most commonly recommended way across all the EFI forums of observing the fuel pressure under ACTUAL driving conditions.
Engine loads while driving can not be duplicated while stationary

 

[Slicktop]

That is not necessary with a high pressure system. The fuel pump provides pressure well in excess of needed pressure and the FPR regulates that pressure down to the desired pressure. If the system maintains the proper pressure with the car stationary it will do it under all conditions because the fuel pump has excess capacity. No FSM or repair manual ever suggests running a fuel line up to the ****pit area and taping a fuel test gauge to the windshield. If a hose clamp started leaking, a line split, or the test gauge ruptured internally fuel could spray all over the ****pit area, which could produce a crispy critter. Also, an accident could easily produce like results if raw fuel was pumped into the ****pit area. Use a little common sense........

 

[vetteoz]

The fuel pump provides pressure well in excess of needed pressure and the FPR regulates that pressure down to the desired pressure.....

Many with fuel problems have noted a loss of pressure when driving that was not evident at idle
Seems your opinion is at odds with what others recommend

From the SBC EFI Bible
How to Tune & Modify Chevrolet Fuel Injection
http://books.google.com.au/books?id...q=fuel pressure testing while driving&f=false

http://www.buzzle.com/articles/fuel-pressure-test.html

http://forums.corvetteforum.com/c4-...do-you-check-fuel-pressure-while-driving.html

 

[[email protected]]

I agree..I ve done it before as well.[ and found the problem, pressure dropped on higher demand ]...how else can you know what it does under actual load conditions?..? .. of course, be sure your hose and guage are in good condition and safely away from anything hot..oh yeah, and don t smoke!

 

[Slicktop]

I agree..I ve done it before as well.[ and found the problem, pressure dropped on higher demand ]...how else can you know what it does under actual load conditions?..? .. of course, be sure your hose and guage are in good condition and safely away from anything hot..oh yeah, and don t smoke!

Yeah, but I will bet that was on your C3 with a low pressure system and no FPR. With a high pressure system a bad FPR will show itself immediately on your test gauge. Also, if you were worried about load it is easy to put a engine under load without driving it.
Always assume that the unexpected can happen. I would hate to see someone turned into a crispy critter. Just because you did something does not make it stupid....During my AF career I was a Wing flying safety officer for a few years and am a graduate of the UCLA Flight Safety School and as such still look out for safety problems. I would never advise someone to do anything unsafe, and personally would never pipe fuel under high pressure into or near the cabin......
The OPs problem is probably ign related anyway, all he needs to do to verify that is to put a timing gun on it. If the timing is spot on and not erratic then move on and suspect the fuel system and check it properly and safely. On a side note I have seen cars and garages burnt to the ground because of people playing with fuel systems. If you do open up fuel lines or spill fuel in your garage and the hot water heater is in there turn off the pilot light immediately or it can easly ignite the fumes.

 

[toobroketoretire]

The fuel pump provides pressure well in excess of needed pressure.

Huh? Since when does a pump produce pressure? To produce pressure you need a force and a restriction and the pump alone won't produce anything but moving fluid.

And Slick, there's NO WAY you can load an idling engine to duplicate actual running conditions. Just because a fuel pump can deliver enough fuel to an idling engine doesn't mean it can keep up with an engine running at full throttle. And the only way you can tell is by observing the pressure under full throttle.

 

[Slicktop]

Huh? Since when does a pump produce pressure? To produce pressure you need a force and a restriction and the pump alone won't produce anything but moving fluid.

And Slick, there's NO WAY you can load an idling engine to duplicate actual running conditions. Just because a fuel pump can deliver enough fuel to an idling engine doesn't mean it can keep up with an engine running at full throttle. And the only way you can tell is by observing the pressure under full throttle.

The pumps pressure can be measured if you block its output with a test gauge upstream of the FPR. High pressure fuel systems are designed so that the pump has much more capacity than needed and then the FPR regulates the pressure down.. As an example the 300zx fuel pump cut off discharge pressure is 61-71psi regulated down to 30psi at idle by the FPR and 37 psi when you step on the gas. For a 94 corvette I only know the regulated pressure since it appears that GM does not advertise the pumps cut off output pressure but I am sure that it has to be at least 30psi above the regulated pressure. If the regulated pressure is correct but you still think that you have a fuel delivery problem you do a fuel flow check which should be 1/2 pint or more in 15 seconds for an 94 corvette........that is the correct and safe way to check for adequate fuel delivery capacity.
Like I said earlier the OPs problem is most likely ign related but you have posted this stuff about piping fuel into the ****pit area many times and I just decided that enough is enough. It is an absolutely unsafe procedure. If you want to take chances, fine, but do not tell other people to use shadetree ideas. You will never see any FSM or repair manual advocate what you recommend, because it is not safe, PERIOD!

 

[[email protected]]

Yeah, but I will bet that was on your C3 with a low pressure system and no FPR. With a high pressure system a bad FPR will show itself immediately on your test gauge. Also, if you were worried about load it is easy to put a engine under load without driving it.
Always assume that the unexpected can happen. I would hate to see someone turned into a crispy critter. Just because you did something does not make it stupid....During my AF career I was a Wing flying safety officer for a few years and am a graduate of the UCLA Flight Safety School and as such still look out for safety problems. I would never advise someone to do anything unsafe, and personally would never pipe fuel under high pressure into or near the cabin......
The OPs problem is probably ign related anyway, all he needs to do to verify that is to put a timing gun on it. If the timing is spot on and not erratic then move on and suspect the fuel system and check it properly and safely. On a side note I have seen cars and garages burnt to the ground because of people playing with fuel systems. If you do open up fuel lines or spill fuel in your garage and the hot water heater is in there turn off the pilot light immediately or it can easly ignite the fumes.

actually no, it was on my Supercharged/ Fuel injected T-Bird, which I still have...but I ve done it a couple times before.. carbureted and fuel injected cars.. you can do it safely,just use common sense,... and you will be surprised at what pressure does under different load conditions and volume of flow

 

[Slicktop]

actually no, it was on my Supercharged/ Fuel injected T-Bird, which I still have...but I ve done it a couple times before.. carbureted and fuel injected cars.. you can do it safely,just use common sense,... and you will be surprised at what pressure does under different load conditions and volume of flow

This poor guy was testing his fuel pressure per your way when he had an accident:

http://classiccarcollectornews.com/blog/2012/10/02/corvette-driver-catches-fire-in-tempe-az-crash/

 

[[email protected]]

he was rear ended by a truck ... I don t recomend that...LOL!

 

[[email protected]]

Slick take a look at this video.. same problem. suspected fuel pressure issue.. pressure gauge vbisible while driving..watch what happens when driver goes WOT .. pressure drops from 30 s to 8 psi.. problem isolated , problem soved http://www.youtube.com/watch?v=9Wc0yaE9VX0

 

[Slicktop]

Slick take a look at this video.. same problem. suspected fuel pressure issue.. pressure gauge vbisible while driving..watch what happens when driver goes WOT .. pressure drops from 30 s to 8 psi.. problem isolated , problem soved http://www.youtube.com/watch?v=9Wc0yaE9VX0

Right, his comment at the beginning is right on, "This is not the safest way to do things". You know that I am right, the point is, is it the safe way to do it, not does it work.

 

[[email protected]]

It does work, obviously,it immediately showed him the huge drop in pressure on higher demand.. and I still maintain that it can be done safely with a little preparation...but, as in all things, do what you feel comfortable with...besides, if we all were only concerned with the safest way to do things, no one would have invented Nitrous Oxide!! LOL!