flannel_man

We're scratching our heads on this one. Went for a drive after lubing the caliper slide pins, engine light came on. Idle was smooth as glass. Add any throttle and it would bog down and sputter and gargle and pop. It had no power unless it was floored and even then it was way beyond underpowered for the 383 crossfire.

My friend was following in his C7 GS and said he could hear it sounded like poo. He said every shift had a massive black noxious cloud blow out the exhaust. It ran smooth in 4th and idle tho. He said the cloud didn't smell like oil, coolant, or fuel, but more like some stinky chemical. As if I were running on an insanely high concentration of fuel treatment or with lacquered gas. It was so bad he started following from farther away in his GS since he had the convertible top down. When I got back I noticed the fuel tank level had dropped 1/4 of tank in that 5 mile brake bedding test drive, down from 3/4 to a half

The temps shot up faster than normal for the 383 and were struggling to come down at all from 235 when the fan came on. At least the brake bedding went well and the passenger caliper no longer stuck and wanted to throw it in the ditch under hard braking and the car would slowly start to roll @ unlevel stops in neutral or clutch in

So,
If it were just a simple fueling issue why would it run like butter at idle and smooth when in 4th gear? It lights instantly on start-up and goes straight to a no vibration silky smooth idle. If it were a massive vacuum leak why would it run smooth at idle or only in 4th? Fuel pressure is set to 13psi, confirmed by @Buccaneer Fuel pressure gauge kit, timing set to approximately 11⁰ with computer wire unplugged when set. If it were bad plug or wire, it wouldn't be able to idle smooth.

Unfortunately I haven't had a day off since it happened Sunday and won't have a day off until next Monday. Trying to figure out a game plan on what to check out. Was planning on flushing the cooling system and putting the aluminum radiator in and a new thermostat, but if it's running like this I wouldn't be able to have it idling for an hour or 3 during the flush process unless I were to just sit and stare at the dash the whole time to make sure it didn't have a huge temp swing or run out of fuel in 20 minutes

'78CorvetteS.A.

What's the code for the "engine light"!?

flannel_man

Don't know. Had to run after returning, won't be off till Monday to to check it

Buccaneer

Wait a minute... Are you saying that you have a 383 and you are running it at 13psi with stock injectors and stock ECM?

'78CorvetteS.A.

Excellent point! I was asking about the code number because the original post doesn't exactly come out and say it, but leads a person to believe/assume it was running perfectly fine as set up and then suddenly after unrelated maintenance it wasn't running right! But yes, I know from the personal advice you gave me on a 383 crossfire build that the stock fuel system/parts/capabilities fall short of feeding a 383 adequately!👍

flannel_man

Correct. 383. Can't remember which Comp Cam CFIEFI recommend for the build way back in 2010 after the lower radiator hose blew and temps were @ 325 and head gasket went on the interstate. Running an 85 fuel pump, stock ECM, fuel set at 13 psi according to Buc's gauge setup, and approximately 11 to maybe 11.5⁰ timing depending on the light

Ran good until this spring, found split vacuum line to ball after having it down a few months for the repaint. Then light came on after the caliper work leaving the driveway for a pad bedding drive. I might be leaving some performance on the table without your ECM upgrade to tune, but it's just a DD now days, I haven't done cones since starting a family. Maybe this winter I'll find some big coins to go that route

Mostly looking for ideas on what to look for when I'm off again and able to look at it

Edit: fuel filter was replaced last year

Buccaneer

Regardless of how much you are leaving on the table or a daily driver, a 383 with stock injectors, bore and ECM will NOT perform well. I run my 383 at 30psi, externally regulated and it really needs to be a bit more actually. I'm willing to bet that you are running way to lean across the table with that pressure and CFM. You can not raise the pressure high enough with a stock regulator without running a significant risk of rupturing the diaphragms in the TBs and having fuel going everywhere on a hot motor and catching fire. DON'T DO IT! You MUST go externally regulated to be safe with a higher than 13/14psi. GM only recommends going to 13, but that is to keep them safe from lawsuits back then. Good luck with your 383 and be safe.

Tom400CFI

....OR put in bigger injectors and continue to use reasonable fuel pressures to achieve a similar result. That was the path I took on my CFI 400. That worked OK and was cheap (~$90 for two injectors).

EDIT: looks like they're ~$170 on ebay these days.

flannel_man

Well I might have found the smoking gun


Vac line at MAP

I know this line passed the smoke test last fall, I disconnected it at the rear TB and hooked it up to the smoke machine for a minute or 2 and it had no leaks. Has all new line now. All that's left to replace is the 3/8" moulded one from the manifold to PCV, and where it steps down to the 3way check valve. Didn't get a chance to drive it since I flushed the cooling system and swapped in an aluminum radiator until the thunder made me look up and I saw the storm clouds rolling in. Finished hooking all the cooling lines up to the radiator just in time to fire it up and roll it 20 ft back into the barn as the rain started to come down. No engine light for that short bit. Tomorrow I'll try and run to town and get the 3/8" then all the vacuum lines will be less than a year old

Tokuzumi

The joys of owning old cars. Things made of rubber are constantly being replaced. Replaced the vacuum lines on my 280ZX over the weekend. Some lines were still pliable, but the lines that required intake elbows to be removed would crumble where they attach to the vacuum ports.

I even need to pull the plenum on my ZR-1, as I went to start it up the other day, and heard a hiss....lifted the hood to find this;

flannel_man

So today I took my list of all the vacuum lines and lengths to the part store and bought up the assortment of sizes. Now every vacuum line is new rubber, and I'll be daily driving again 👍🏻

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