Originally Posted by Tripler (Post 295290)

Hey guys/gals . Was driving the 1995 Z today and all of a sudden the engine lost power and developed a ruff idle . It also seemed to be running on very few cylinders . It was working fine on the highway but once I got close to home , it began the loss of power and ruff idle in city traffic . Would a gas cap not being tight enough create this issue ? Also could it be the fuel filter ? It has a half filled gas tank and car always gets Shell 91 octane Ethanol free gas .



Thanks

Mike

Originally Posted by secondchance (Post 295291)

Hi Mike!

Did it backfire? First, I would check MAP sensor hose between the MAP sensor and the back of the plenum.
Loose gas cap wouldn’t cause symptoms you are seeing.

Originally Posted by dredgeguy (Post 295292)

Hi Mike, sounds like a problem I had in the past. One of the fuel pump hoses was loose and just hanging. The fix was new hose clamps. Good luck and keep us posted.

Originally Posted by Tripler (Post 295319)

Morning. A small hard black hose was not attached to a softer rubber 90 elbow. Is that the MAP Sensor ? . I reconnected it but still runs a bit ruff . Do I need to take it for a drive to reset everything ? Should I be looking for anything else ?
Mike

Originally Posted by dredgeguy (Post 295341)

Sure thing but sometimes dreams can turn into nightmares. Have a few stories to tell you at Carlisle. Flying down the middle of the Straits of Hormuz and cutting east over Iran in a 777 when missiles are in the air will keep the pucker factor very high!

Originally Posted by secondchance (Post 295327)

A small hard black hose was not attached to a softer rubber 90 elbow. Is that the MAP Sensor ?

Was this hose between the back of the plenum to underside of MAP sensor? MAP sensor is under an aluminum trim behind the plenum. Once reconnected, all should return to normal. If not, I suspect something else blew off under the plenum on top of MAP sensor hose when it backfired.

Originally Posted by Tripler (Post 295403)

Drove it around the block . Feels like a 6 or 4 and is still running ruff . Bought a video scope to look under the plenum .
Also on another note , the car only backfired 3 or 4 times since we have owned it since 2016 and it would only do it going down a hill with my foot off the gas pedal in second gear, just a small pop but it did not always happen . Just once in a blue moon .
Mike

Sent from my ASUS_X00PD using Tapatalk

Originally Posted by secondchance (Post 295405)

If you hear a pop going down hill with foot off, my guess is unburned fuel mixture going downstream and lighting up. This should not cause MAP blow-off. MAP sensor hose blows off when you back fire during the engine start.

Again, it's just a WAG - if MAP hose is intact and still suffering from misfire, either a fuel system issue (like fuel pump, clogged fuel filter, etc.) or a vacuum blown under the plenum.
I presume CEL is not on? Can you see if you can jump OBD and pull code?

Originally Posted by Paul Workman (Post 295415)

If that MAP hose(s) were disconnected and now restored, I'd wanna pull and inspect the plugs. Could be some plug(s) got fouled and will run OK when they are cleaned up.

Experience is generally a good thing when troubleshooting; it can lead one to the issue sometimes immediately. But! If guessing at the solution proves not to be the case (fix), it"s back to the basics time!

FUEL PRESSURE (static) = ?
Current draw on the pump diagnostic test point (red wire about 5cm long w/ a black terminal sticking out of the large wire loom near the W/S wiper motor) when ignition key is in the OFF position [8-10 amperes is normal for both pumps running nornally].

Let us know what U find...

Originally Posted by Paul Workman (Post 295416)

Next:

When you shut off the ignition switch, does fuel pressure hold to within a pound or two for 10-15+ minutes, or drop to zero briskly?

Originally Posted by Tripler (Post 295434)

How would I check fuel pressure ? Do I need to attach a gauge somewhere along the fuel line ?



Thanks



Mike

Originally Posted by Ccmano (Post 295442)

Is that elbow in the vacuum line to the fuel pressure regulator? If there’s gas there the fuel pressure regulator has failed, could be the source of you problem.

The “spigot” you refer to (if I interpreted you post correctly) is the vent for the vacuum solenoid. No lines attach there.
H

Originally Posted by Paul Workman (Post 295447)

There is a Schrader valve at the front of the passenger side fuel rail. Attach a pressure gauge there for static pressure tests, (AND (FYI) if you purchase an extension hose, you can do impromptu dynamic tests by taping the pressure gauge to the windshield and going for a drive (not necessarily applicable to this particular problem))

Originally Posted by Tripler (Post 295474)

On another note , is there a trick to getting plugs out of an LT5 ? I tried 2 that were easily accessible and had no luck . Maybe my old arthritic hands have lost there old man strength lol .

Mike

Originally Posted by 32valvZ (Post 295477)

try a 1/2" set up with a breaker bar.

Originally Posted by Tripler (Post 295481)

Agree but is there an off chance that the larger wrench would break the plug off ? That was my concern . Not used to working on this beast as I only work on small car engines and motorcycles mostly and did not expect these plugs to be as tight as they are . Yikes .

Thanks for the tip.


Mike

Originally Posted by Tripler (Post 295455)

So from what I am reading and from what you guys are saying , the fuel pressure regulator is toast . Any idea where I purchase a new one and also how difficult are they to change out .



Is this the right one ?
https://www.ebay.com/itm/Fuel-Inject...oAAOSwxMRbnQfo


Also reading Dynomites blog .
https://www.corvetteforum.com/forums...post1596384563



Thanks



Mike

Originally Posted by Tripler (Post 295491)

Just looking over Phil's amazing build !

http://www.zr1.net/forum/showthread.php?t=28304

Originally Posted by Ccmano (Post 295497)

Agreed the eBay one will not work. Unless you find a correct one on eBay or someone is gracious enough to sell one out of their stash, contact Phil and see if he will repair yours.



I use this setup for the #8 plug, a straight extra long extension works for the rest. Notice that the spark plug socket has the universal built in. When unseating a plug I use a quick snap of force against the ratchet handle to get them unseated.



http://a65.tinypic.com/311t654.jpg



Paul rightly points out that if you do a fuel pressure test, not looking so much actual pressure, but if the fuel pressure bleeds off quickly when the pumps shut down, that’s another indicator that the pressure regulator is bad.

H

:cheers: