Home page
SPONSOR AD

Support our Vendors!  |  Advertise Here

Topic: My 84 runs great ,then sh$t hits the fan!!

in Forum: C4 General Discussion


Already a Member?
Login
Not yet a Member?
Register for Free!

My 84 runs great ,then sh$t hits the fan!! (1/10)
 10/31/15 10:02pm
gjohnson
Standard Member
Send Private Message

denver, CO - USA

Vette(s):
1976 & 1984


Joined: 10/31/2015
Posts: 5

As a C-3 owner for 25 yrs the time had come to get a new toy.I picked up a low mi. 84.Passed emissions easily. Runs killer for about 30 min or so then starts spittin and sputtering and popin thru the TB. Also seems to be running on 6 cyl. Did a visual and the injectors are sputtering fuel in unision.Let it cool down and back to normal. Seems to be heat related. SEL doesn't light and throws no codes. I have replaced the following:
 
Cap/rotor/ICM/plugs/wires
ECM coolant temp sensor
MAP sensor
Fuel pump/sender/sock/filter
Cleaned fuel tank
 
Any help appreciated. Thanks
Our Sponsors help support C4VR
Re: My 84 runs great ,then sh$t hits the fan!! (2/10)
 11/1/15 1:12am
Hot Rod Roy
Standard Member
Send Private Message

Mission Viejo, CA - USA

Vette(s):
Yellow '84 Coupe


Joined: 3/18/2015
Posts: 74

I know you've replaced the fuel pump, but your "spitting injectors" makes me wonder about your fuel pressure.   Could be other causes, but it's good to know your FP is good.   Is your FP relay and connector in good condition?   It's tricky to test FP on an '84.    The best way I know to test FP is to remove the fuel filter, and put a rubber hose in its place which has a "T" in it.   Connect your FP gauge to the "T".

Have you checked your O2 sensor?   Here's an interesting write-up:
http://www.autotap.com/techlibrary/understanding_oxygen_sensors.asp





|UPDATED|10/31/2015 10:12:44 PM (AZT)|/UPDATED|


______________
Re: My 84 runs great ,then sh$t hits the fan!! (3/10)
 11/1/15 3:10am
gjohnson
Standard Member
Send Private Message

denver, CO - USA

Vette(s):
1976 & 1984


Joined: 10/31/2015
Posts: 5

I did also put a new O2 sensor and cat. Will have to check the fuel pressure when it acts up cause its at 14 when running fine. Thanks for the reply.
Re: My 84 runs great ,then sh$t hits the fan!! (4/10)
 11/1/15 5:11pm
Don
Standard Member
Send Private Message

Bolivia, NC - USA

Vette(s):
1993 Torch Red Convertible black int, black top, 6 speed, optional luggage rack.


Joined: 3/28/2015
Posts: 6

Could be the coil.  I had problems years ago with a bad coil. Had the same symptoms Drove me nuts til I finally changed the coil.


______________

Re: My 84 runs great ,then sh$t hits the fan!! (5/10)
 11/1/15 7:25pm
gjohnson
Standard Member
Send Private Message

denver, CO - USA

Vette(s):
1976 & 1984


Joined: 10/31/2015
Posts: 5

Replaced coil today. SameCensored
Re: My 84 runs great ,then sh$t hits the fan!! (6/10)
 11/2/15 1:56am
Hot Rod Roy
Standard Member
Send Private Message

Mission Viejo, CA - USA

Vette(s):
Yellow '84 Coupe


Joined: 3/18/2015
Posts: 74

gjohnson said: Will have to check the fuel pressure when it acts up cause its at 14 when running fine. 

Did you find a better way to check FP?  I'm always looking for better answers!



______________
Re: My 84 runs great ,then sh$t hits the fan!! (7/10)
 11/2/15 9:39pm
gjohnson
Standard Member
Send Private Message

denver, CO - USA

Vette(s):
1976 & 1984


Joined: 10/31/2015
Posts: 5

I'm gonna tee the fuel line and run it up w/gauge and tape it down between hood and windshield and drive it till it acts up. I will then see the pressure  in real time.
Re: My 84 runs great ,then sh$t hits the fan!! (8/10)
 11/4/15 2:11pm
Black Shark
Standard Member
Moderator
Send Private Message


Vette(s):
Black 1979 L-82 Black 1996 LT1 Black 1999 Coupe


Joined: 3/20/2009
Posts: 611

gjohnson said: I'm gonna tee the fuel line and run it up w/gauge and tape it down between hood and windshield and drive it till it acts up. I will then see the pressure  in real time.



^^Good idea.
 
 
did you do a compression test yet?
Re: My 84 runs great ,then sh$t hits the fan!! (9/10)
 11/4/15 3:41pm
wolfuser
Standard Member
Send Private Message


Vette(s):
1987 C4 convertible 350ci auto white / red / white top appx 18k mls


Joined: 11/15/2012
Posts: 13

hi,

seems to me if it runs well for 30mins and then stumbles it wont be compression or such. did you replace the fuel pump relay? 
temp thing could hint at temp sensor. you might want to check engine temp sensor and intake air sensor.... if the fuel injection gets wrong info in this area the ecu might think car is cold.
if you look in the service manual, there are sensor resistance data.
nonetheless, might be interesting to verify ignition timing/dwell when she doesnt run well. spitting back could mean wrong timing.

good luck
Wolfram
Re: My 84 runs great ,then sh$t hits the fan!! (10/10)
 11/5/15 3:26pm
Tesla220
Standard Member
Send Private Message

Joined: 4/23/2015
Posts: 64

Pump relay only supplies power to the pump when you are cranking the engine to get it started and then for 3 seconds more. After that the fuel pump is powered through the oil pressure switch. You can pull the Pump Relay out and throw it in the trash after the engine is running and the engine will continue to run. 

Try tapping on the ECM when it is running well. If the engine sputters badly you need an ecm, have seen this many times with GM ECM's of that era. Also tap on it when it is running badly and observe if there is any significant change in engine performance.

Also for that generation Vette there was a problem with wiring behind the cylinder heads and firewall, check this by shaking the wiring harness while it is running and observe for changes in performance

While it's running real bad unplug the vacuum to the EGR Valve to be certain it is not opening fully when going into "Closed Loop".  ACTUALLY THIS WOULD BE THE FIRST THING I WOULD DO. Sorry for making it the last item of my short list.





|UPDATED|11/5/2015 12:26:07 PM (AZT)|/UPDATED|


______________
ASE Master Certified, L1 Certified, Owner/Tech
Track Day Rat
80 4Speed 
96 LT4

If you're never out of control you're not driving fast enough  
Our Sponsors help support C4VR