Any 1984 vette guru's?

[DaveN]

Dad bought a 1984 vette with 12,000 miles on it last fall. Looks showroom fresh. But it sat for 10 years, so he spent all last fall replacing all of the fluids, rubber, etc etc. Last fall he had it running pretty decent - not tip top, but he went on a few short trips with it with no problems.



He goes to start it up this sping, it warms up and runs like crap. So he calls me, and I tell him to try new gas (first step for me always). He mentions it's low on gas, so yeah it could be bad gas, fills it up with premium and two cans of drygas. Drives it home, tries to open it up to get the old stuff out of the lines - no luck. Coughing and farting the whole way.



I finally show up after he gets it home, we start it up, it was warm, but not hot. Probably 100 degrees or so. Starts fune, runs and idles fine. I'm playing with the thorttle linkage, revs up fine, no misses, etc. I'm watching it run with the air cleaner off, vaccum line plugged. Running great. Fan kicks on, about 30 seconds later the idle kicks up, and it starts running REALLY rich. We shut it off, and you can hear fuel flaming out in the exhaust.



I'm thinking that either its the engine temp sensor, or something else that engages when the engine gets to full temp (that of course isn't working right)... . Any ideas?



Thanks-



Dave

 

[HoleshotHolset]

Let's see... '84 Vette = 350cid w/throttle body injection ('Crossfire' style)...



Good luck! OK, that wasn't nice... let's try to help now.



Have you checked the fuel pressure? Those don't run very high pressure... 13-15psi or so. It might be too high (bad regulator?).

Stuck injector(s)? (at least the injectors are cheap money to buy... and there's only two of them!)

Is the thing putting out any codes? You can check 'em with a paperclip and a book...

Have you put it on a scan tool yet? Check the MAP (Manifold Absolute Pressure) sensor output... this is a speed density system and relies HEAVILY on that sensor... and having a good vacuum signal to it!

Bad oxygen sensor? - again, scan tool will find that.



Almost sounds like it's going into 'closed loop' (when the O2 sensor finally heats up and provides feedback to the ECM) and begins running like dog poo straight away... interesting.



Be sure to check the wiring leading to/from the ECM... mice have been known to chew through a single wire... causing similar foul-ups.



I like Vettes and would be glad to offer more help if you need it...



Matt

 

[DaveN]

Well, it's not tripping any check engine lights. Code wise I'm not sure, I can see that we're going to have to move into the 80's technology and accept that things are computer controlled now..... we're used to working on pre-74 engines... .



If it's putting out codes, won't the service engine light come on?

 

[HoleshotHolset]

Dave: You're right... if the ECM had hard codes... the light should come on. That begs a question... does the 'check engine' light ever come on at all?



I'd like to see you put that thing on a scan tool... that way you could see the feedback from all of the various sensors I mentioned before in realtime.



Make friends with someone who has a Snap-On MT-2500... or other similar scan tool. For diagnosing a drivability issue like this you really need one; otherwise you'll just end up throwing a bunch of parts at it.



Matt

 

[DaveN]

Talked with Dad last night - he never got any lights at all. Last fall he replaced the engine temp sensor, but he told me (finally) "I bought the cheap one... . " I guess he went out and bought "the good one" (throwing parts at it) and he says it's running great now... .



I figured it had to be somethign temp related, since it started when it reached full temp. So I think at that point he started putting 2 and 2 together and realized that there must be a difference between the $10 sensor and the $30 sensor...



Thanks for the help Matt!

 

[HoleshotHolset]

Well... I'm glad you got it up and running for cheap!

Gotta love those fixes...



Matt

 

[ProspectorTim]

Ya gotta love the quick & easy ones!



FWIW, anytime you need help with the 'vette - the Corvette Forum is the Corvette equivalant to TDR for Dodge/Cummins trucks.



You will find a lot of good, very helpful people over there.

Sometimes you might find me over there too; but I sold my '87 last summer.

 

[Hohn]

I think the word for someone with an L98 (esp 1984) is "victim", not guru :-laf



J/k-- 'vette quality control was pretty bad in that year.