Help engine problems!
Thread Starter
Cruising
Joined: Sep 2011
Posts: 12
Likes: 0
From: Seymour Tn
Help engine problems!
I just bought my first Vette(1986 Yellow Convertible). I new it had some problems when I bought it. It ran very rich, missed bad and backfired. Brought it home and did a basic tune up. Found that the rotor had the metal melted to the plastic. Put nrw injectors in it. Also put it on a scanner and read MAF sensor bad. Put new Maf in it, new IAC. Started it up and ran ok for a couple of minutes then started running rich,missing bad and backfiring. Then it would not idle unless I diconnected the MAF sensor. It idled then but still ran horrible. Somtimes when I start it would rev to high rpms stay there for a couple seconds before slowly comming back down and stalling. Getting frustrated, any help would be greatly appreciated. Could it possibly be the ecm I checked and it has the original in it.
Instructor
Joined: Jun 2011
Posts: 182
Likes: 0
From: Bowling Green Ky
I just bought my first Vette(1986 Yellow Convertible). I new it had some problems when I bought it. It ran very rich, missed bad and backfired. Brought it home and did a basic tune up. Found that the rotor had the metal melted to the plastic. Put nrw injectors in it. Also put it on a scanner and read MAF sensor bad. Put new Maf in it, new IAC. Started it up and ran ok for a couple of minutes then started running rich,missing bad and backfiring. Then it would not idle unless I diconnected the MAF sensor. It idled then but still ran horrible. Somtimes when I start it would rev to high rpms stay there for a couple seconds before slowly comming back down and stalling. Getting frustrated, any help would be greatly appreciated. Could it possibly be the ecm I checked and it has the original in it.
coolant temp sensor can cause rich condition. 14 or 15 I believe. but not backfiring. that sounds like timing, or plug wire issue. is it thru intake or in the exhaust system?
fuel pressur regulator can leak into the vac line which comes from plenum, I think would show as rich condition too.
start with codes and get back.
jc
you set the TPS I assume, if you replaced iac. affects idle but not rich.
Last edited by stoydido; Sep 6, 2011 at 11:22 AM. Reason: spell
Thread Starter
Cruising
Joined: Sep 2011
Posts: 12
Likes: 0
From: Seymour Tn
Backfiring thru intake. Set timing. No fuel in regulator vacumj. Did not reset iac. Showing no codes. I did find a broken plastic vacum line near firewall on drivers side, cant find where it goes.
Instructor
Joined: Jun 2011
Posts: 182
Likes: 0
From: Bowling Green Ky
that can explain the idle issue, possibly the backfire if intake gets leaned out, may be wrong there, as the o2 sensors would try to compensate.
might wind up rich.
these c4's can get complicated!
a struggle just to hold stuff in your brain.did it ever run ok after injectors installed?
Thread Starter
Cruising
Joined: Sep 2011
Posts: 12
Likes: 0
From: Seymour Tn
may be an accumulator line that serves several lines, one is from the vac cannister, also serves the MAP on 91 models, your version of MAF, maybe the fuel reg also. definitely need to find the other end of it which will be a leak source.
that can explain the idle issue, possibly the backfire if intake gets leaned out, may be wrong there, as the o2 sensors would try to compensate.
might wind up rich.
these c4's can get complicated! a struggle just to hold stuff in your brain.
did it ever run ok after injectors installed?
that can explain the idle issue, possibly the backfire if intake gets leaned out, may be wrong there, as the o2 sensors would try to compensate.
might wind up rich.
these c4's can get complicated!
a struggle just to hold stuff in your brain.did it ever run ok after injectors installed?
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
before the ecm I would find backfiring as ign issues, crossed wires, arcing in dist cap, whatever. or lean air/fuel mix.
have to locate the missing vac line, because it won't run well without it connected. I am not familiar with the 86 enough to suggest what to look for. other than check the ones you removed in the inj change.
Race Director
Joined: Apr 2003
Posts: 17,698
Likes: 1,667
From: moraga ca
the fan only comes on at 248* or so, or until you jumper it as you did.
before the ecm I would find backfiring as ign issues, crossed wires, arcing in dist cap, whatever. or lean air/fuel mix.
have to locate the missing vac line, because it won't run well without it connected. I am not familiar with the 86 enough to suggest what to look for. other than check the ones you removed in the inj change.
before the ecm I would find backfiring as ign issues, crossed wires, arcing in dist cap, whatever. or lean air/fuel mix.
have to locate the missing vac line, because it won't run well without it connected. I am not familiar with the 86 enough to suggest what to look for. other than check the ones you removed in the inj change.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
Thread Starter
Cruising
Joined: Sep 2011
Posts: 12
Likes: 0
From: Seymour Tn
I did plug it. Could it be the ignition coil causing it to backfire and not idle. I noticed a screw missing on the cover today and noticed some rust on the metal plate surrounding it.
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
the issues are rich, not idling, backfire. not sure the coil is the first place to look for either of those. don't see how we can ignore the iac.
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
also, unless you marked/numbered the dist ends of your wires, it is possible one is crossed. happens a lot.
another also, plugging a vac hose is fine IF it is the end that goes to the vac source.
it is so easy to overlook some little thing so I have to mention them. the backfire look like ign, timing, whatever. spark fires while intake is open.
joe
another also, plugging a vac hose is fine IF it is the end that goes to the vac source.
it is so easy to overlook some little thing so I have to mention them. the backfire look like ign, timing, whatever. spark fires while intake is open.
joe
Thread Starter
Cruising
Joined: Sep 2011
Posts: 12
Likes: 0
From: Seymour Tn
also, unless you marked/numbered the dist ends of your wires, it is possible one is crossed. happens a lot.
another also, plugging a vac hose is fine IF it is the end that goes to the vac source.
it is so easy to overlook some little thing so I have to mention them. the backfire look like ign, timing, whatever. spark fires while intake is open
joe
another also, plugging a vac hose is fine IF it is the end that goes to the vac source.
it is so easy to overlook some little thing so I have to mention them. the backfire look like ign, timing, whatever. spark fires while intake is open
joe
Have anything to do with my problems?
Thread Starter
Cruising
Joined: Sep 2011
Posts: 12
Likes: 0
From: Seymour Tn
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
only by adding another problem to the several you have.
it starts, alternator resupplies voltage, starts again.
that's all the battery is expected to do. the engine should run fine with battery disconnected.
coolant temp sensor can fail, if reading is -49* the ecm will add fuel, engine runs rich. generally, code 14 would set.
it starts, alternator resupplies voltage, starts again.
that's all the battery is expected to do. the engine should run fine with battery disconnected.
coolant temp sensor can fail, if reading is -49* the ecm will add fuel, engine runs rich. generally, code 14 would set.
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
it has to be adjusted. no fsm or haynes? there is a documented procedure on the "sticky's" on discussions forum. check it out. I am almost certain the engine will not idle without it being set.
*** we are talkin' Idle Air Control, not ICM, engine module. correct?
*** we are talkin' Idle Air Control, not ICM, engine module. correct?
Last edited by joe paco; Sep 6, 2011 at 06:55 PM. Reason: add***
Thread Starter
Cruising
Joined: Sep 2011
Posts: 12
Likes: 0
From: Seymour Tn
only by adding another problem to the several you have.
it starts, alternator resupplies voltage, starts again.
that's all the battery is expected to do. the engine should run fine with battery disconnected.
coolant temp sensor can fail, if reading is -49* the ecm will add fuel, engine runs rich. generally, code 14 would set.
it starts, alternator resupplies voltage, starts again.
that's all the battery is expected to do. the engine should run fine with battery disconnected.
coolant temp sensor can fail, if reading is -49* the ecm will add fuel, engine runs rich. generally, code 14 would set.
Thread Starter
Cruising
Joined: Sep 2011
Posts: 12
Likes: 0
From: Seymour Tn
Yes the IAC. Just bought a Haynes going to try and reset thanks.
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
the IAC is simple with the haynes, that may cure the idle issue. I would verify all the ign parts if it was mine, wiring, plug wires, if it runs, the module and pickup coil are ok.
