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Help! 86 corvette won't start - help!

Fatchy

Member
Joined
Jan 3, 2012
Messages
9
Location
South Carolina
Corvette
1986 Dark Red Coupe
This is my 1st corvette - 86 coupe with L98 engine....as far as I can tell, mostly stock. Bought in January of this year. Last Saturday drove 50 miles, filled up 15 gals premium, drove 125 miles, topped off with premium at same gas station then drove another 50 miles....no problems, ran smooth. On Tuesday, started up car to move from driveway to garage...no problems. Thursday morning went to start up & the car would run for ~2 seconds then stop....tried lots of different throttle positions but no go. No trouble codes at this point.

Actions & diagnostics taken so far:
Replaced fuel filter, fuel pump relay & fuel pump - -- still won't start & now won't even run for 2 seconds like before (cranks but won't catch).
Fuel pressure is 47psi with pump running...drops to 43 psi when pump stops but holds pressure.
Removed plug & checked for spark - ok. Then checked distributor cap & rotor. Found the spring/center contact spring broken. Replaced cap, rotor & ignition coil. Still doesn't start.
Tested fuel injectors with Noid light....when cranking the noid light flashes as it should.
Tested resistance of all 8 injectors....16.0 to 16.1 ohms.
Checked the TPS sensor....voltage was a little high -- 0.6v so I adjusted to 0.53 volts.
Tried using starter fluid (not good practice) but the engine did fire but stopped as soon as the starter fluid stopped.
Thru all of these tests, I did not get any trouble codes. I tried to start this morning but no go......but I finally got a trouble code...34 - MAF flow sensor low. Now What???
 

John Robinson

Gone but not forgotten
Joined
May 3, 2005
Messages
1,555
Location
Muncie, Indiana
Corvette
1993 Polo Green Coupe
Dont jump at the sensors check all the wiring to ground connections and clean the grounds. The code is telling you something is wrong in that particular circuit not that the sensor is bad. The problem is that the TPS the Map and several other sensors have a common ground back in the wiring bundle. The ECM is simply telling you were to start it has adjusted everything in that circuit and the only thing it cant get right is the map sensor circuit. Since several sensors share a common ground it could be any one of them causing the problem.
 

Fatchy

Member
Joined
Jan 3, 2012
Messages
9
Location
South Carolina
Corvette
1986 Dark Red Coupe
Dont jump at the sensors check all the wiring to ground connections and clean the grounds. The code is telling you something is wrong in that particular circuit not that the sensor is bad. The problem is that the TPS the Map and several other sensors have a common ground back in the wiring bundle. The ECM is simply telling you were to start it has adjusted everything in that circuit and the only thing it cant get right is the map sensor circuit. Since several sensors share a common ground it could be any one of them causing the problem.

Thanks for the quick reply....Today being Mother's day & all, I didn't get a chance to do much on the grounds. Found your previous post with all the different ground points, so that will be where I start. I'm just surprised that a ground problem would happen that suddenly. I also need to re-verify the trouble code because I think I may have created the problem when I tried to start up with the starter fluid & disconnected the tube between the MAF & TPI.
 

boomdriver

Well-known member
Joined
Dec 18, 2008
Messages
1,888
Location
texas
Corvette
87 z-51
Thanks for the quick reply....Today being Mother's day & all, I didn't get a chance to do much on the grounds. Found your previous post with all the different ground points, so that will be where I start. I'm just surprised that a ground problem would happen that suddenly. I also need to re-verify the trouble code because I think I may have created the problem when I tried to start up with the starter fluid & disconnected the tube between the MAF & TPI.


Confirm the code 34. Thats an easy fix...MAF relay, and NOT the maf sensor usually.

If thats not an issue, and you DO have 40+ psi fuel at the rails during cranking, and holds pressure for several hours,

and

have confirmed noid lite on BOTH banks, (one side can be down, these are bank-fired injectors, basically 1 inj circuit split 8 ways but divided into 2 banks L & R)

AND have spark tested several wires and seen the blu spark,

Then I'd start pulling plugs to see if they are wet with water and double check for fire on a couple.

Ing module can fail, as well as the spark module by the washer bottle.

Look at ALL your power source leads on the battery jumper post. NOT the pos battery cable..the harness power source leads behind it. Fusable links...
Check all your inj and ecm fuses.
Check all the grounds...again, NOT the battery cables,. the harness grounds. 5 are on the block just over the oil filter...critical.
VATS is not an issue....if the inj were liting the noid lite the VATS module was ok and if the starter was turning the enable relay is good.
Might look at the ECM and prom for plugs/connections.
 

Fatchy

Member
Joined
Jan 3, 2012
Messages
9
Location
South Carolina
Corvette
1986 Dark Red Coupe
Got it running tonight. Finally got a hold of the previous owner.....he highly recommended replacing the Ignition control module. So, I replaced the ignition control module & the engine finally started to run. It was a little rough at first with some backfires but it kept getting smoother the longer she ran. After a couple of minutes it would hold an idle. I then took it for a ride around the neighborhood with no problems. There are no error codes or check engine light now.:happyanim:

John Robinson & Boomdriver thanks for the replies & help.
 

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