84 Runs Bad

[pistonhead]

I just bought an 84' Vette that runs bad. It is very hard to start, idle rpms surge, appears to have a missfire sometimes. But no codes, good fuel spray pattern on the inj. and they don't drip, TPS sensor measures ok any ideas?

 

[silver 80]

EGR?

 

[pistonhead]

EGR code checked ok, diaphram moves freely, rpm's go down when diaphram is manually depressed, is there any other checks for EGR?

 

[pistonhead]

EGR code checked ok, diaphram moves freely, rpm's go down when diaphram is manually depressed, is there any other checks for EGR?

 

[kmcewan]

What is EGR anyway?

Ken

 

[pistonhead]

I believe it stands for Exhaust Gas Recirculation , To the best of my knowledge it circulates exhaust gas through the intake manifold to pemote better eng. worm up.

 

[Twin_Turbo]

EGR reduces NOx by introducing incombustibles and therefore reducing combustion temperature.

pistonhead, check TB balancing, plugwires, fuel pump, system pressure.

http://www.crossfire.webhop.net

Here you can find all the info on your X-fire!

Marck

 

[c4ever]

Pistonhead
I would take a harder look at the EGR. My 82 EGR passed all the basic checks but still had a weak spring. I tried everything before someone caught it. Car runs 100% better than it ever did. Worth a try before digging into all the other possibilities. Also check the THERMAC for proper damper operation. I'm not familiar with the 84 Cross-fire so you may not have the THERMAC.
Best of luck.:cool

 

[69MyWay]

Check engine light,

Are you sure the bulb is good? Are you seeing the service engine soon light when you simply turn the key on? If not, replace the bulb and then pull the codes.

 

[Twin_Turbo]

The 84 has a thermac system justs like the 82. The aircleaner has 2 flaps, one on pass. side is for cold air, the driversside is thermac.

 

[pistonhead]

service engine soon light does work, previous owner pulled it, so I replaced it but throws no codes and only flshes code 12 .

Also does anybody know what the thermac does ? It shouldn't come into effect if the car still runs bad with the air cleaner assembly removed.

EGR spring feels pretty stiff.

 

[evolution]

Try the knock sensor too

My 84 ran like poohay, i.e. valves clacking and crappy idle. New knock sensor, no problems.

Might not be it but if it clacks alot try it.

Tho mine does backfire thru the intake once in a while still trying to figure that one out.

 

[pistonhead]

This one doesn't backfire through the TBI but does appear to have some valvetrain noise. Going through valves right now. Also a friend has a scanner and he ran it through and said the knock sensor and others were working, Unless they could be giving a dummy reading?

 

[c4ever]

Thermac air cleaner uses the damper on the air cleaner inlet to control air temperature to the carb. A temp. sensor locate in the air cleaner assembly closes the damper until air temp at manifold reaches about 100 degrees then slowly opens.

 

[David-F]

Check your IACs there are two on a Crossfire if one sticks the car will have a rough idle because one side is running leaner than the other, just remove the air cleaner assembly, use a flash light and look in the throttle bodies in the trangle hole you will see the pintels of the IAC, now just goos the throttle with the car running and warmed up you should see the IACs retract then extend, both of them and they both should move about a 1/4" at least if not I would recomend you replace both. Also a Crossfire is real bad at fouling out plugs if it gets started and shut down with out having a chance to clear itself out, very rich start up! You may need to also check your plugs and keep them clean, but I bet one of your IACs is stuck.

David Fulcher

 

[David-F]

Also there are no EGR codes on an81 to 84 vette that started in 85 with the use of a temp sensor on the EGR valve itself then moved to the cross over tube in 86 to 89, and after that they use a combination of sensors to determin if it is working.

David Fulcher

 

[Hopper]

Hard cold start

Pistonhead, Have you manually, with a scanner,
checked the cold value of the ECT sensor? I have
replaced many of these ENGINE COOLANT TEMPERATURE
sensors for having a faulty cold start value. Also
the 1984 and 1985 models were known to have too
cold of a coil (via factory bulletin #85-C-22A-6D) Good luck, Hopper..

 

[David-F]

Did I talk about the coolant sensor I just never remember which post I post what, there was a problem with the 82 and 84 coolant sensors they used a barrel connector that was real bad at loosing contact that would just dump fuel when trying to start it you could also get some surging if it was changing on you the fix was a kit that came with the later style sensor that was a two pin sensor and a pig tail, if your car has the round barrel sensor on it just replace it and de done with it. Also the campaign to replace the coil and module and spark plug gap had to do with trying to put tomuch voltage through the wires and over heating the coil and taking it out so they shortened the saturation time of the coil with the new distributor module and then replaced the coil but this also required and reduction of spark plug gap from 0.045 to 0.035, so you might also want to check that you have the correct spark plug gap, that could also give you some problems. Boy there is so much you have to remember on these cars.

David Fulcher

 

[pistonhead]

Thanks for the help guys I'll have to look further.