1986 Corvette Ignition problem

[Jim Hannon]

I have a 1986 Corvette that has a miss and runs rich. In the process of elimination I have tested the coil, pickup coil is new, Cap and rotor new, MSD spark plug wirers test with in range. I hooked it up to a timing light and the spark is very erratic on every cylinder. Timing light is working correctly have tested it on another vehicle. I can not seem to figure this out!!!! Any help will be greatly appreciated.

 

[TedC]

Jim,
Did this all of a sudden happen? Some history would be helpful. Any codes? Did you test the ignition module? Most auto parts stores have testing equipment. Run the test multiple times.

Welcome to CAC!!!

 

[boomdriver]

I have a 1986 Corvette that has a miss and runs rich. In the process of elimination I have tested the coil, pickup coil is new, Cap and rotor new, MSD spark plug wirers test with in range. I hooked it up to a timing light and the spark is very erratic on every cylinder. Timing light is working correctly have tested it on another vehicle. I can not seem to figure this out!!!! Any help will be greatly appreciated.

Like Ted says....check the codes first.

Being rich can be the cause or an effect. A poor spark will make for more emissions but a rich charge might not burn clean as well...

I'd start by cleaning and checking all the plugs and connections to and inside the distributer. After thats all done,. and the module test OK, I'd consider the o2 sensor. A scanner would be helpful about now...

Last, if the car has 150K or more, being an 86, I'd seriously consider spending $250 on a set of Bosch III fuel injectors. Your stock injectors are/were/still junk on their best day and are being replaced as quickly as people can purchase the Bosch from FIC. You might Ohm test the inj to see which ones are out of spec...they should all be close to the same, The spec is here somewhere...do a search here to locate a thread that has it.

If the inj DO test ok, that does not mean that they are spraying well. You can try some techron or Lucas inj cleaner in the next couple tanks of gas, but thats only temporary. Once these old mule-tic injectors get old...they're toast. So are the fuel inj system O-rings..

 

[Jim Hannon]

Jim,
Did this all of a sudden happen? Some history would be helpful. Any codes? Did you test the ignition module? Most auto parts stores have testing equipment. Run the test multiple times.

Welcome to CAC!!!

Now that I have been working on this car I was thinking back and it has seemed to have been running rich for a while. I dont know about the spark issue becaus this is the first time I have messed with the timing. I was setting the base timing after a head swap. Had some valve seal guides leaking. I have not had any codes other than the ones i have produced and have cleared all them. So far I have tested the coil it was good, the ignition module was tested six times it passed, it has new cap and rotor, a new pickup coil, new spark plugs and wires. Thanks alot for the post.

 

[John Robinson]

I don't have any experience with your year car but on my 93 when it started to run rich I replaced the O2 sensor and it corrected the problem. Another area to check is the evap system

 

[vetteboy86]

Now that I have been working on this car I was thinking back and it has seemed to have been running rich for a while. I dont know about the spark issue becaus this is the first time I have messed with the timing. I was setting the base timing after a head swap. Had some valve seal guides leaking. I have not had any codes other than the ones i have produced and have cleared all them. So far I have tested the coil it was good, the ignition module was tested six times it passed, it has new cap and rotor, a new pickup coil, new spark plugs and wires. Thanks alot for the post.

Did you disconnect the EST wire while setting the base timing?

 

[Jim Hannon]

Did you disconnect the EST wire while setting the base timing?

Yes unhooked the EST wire and set the base timing a 6 Deg. BTDC. But did this with the timing light flashing erraticly. I did test the timing light on another V-8 in a chevy truck but it didnt have the HEI dist. and it worked perfectly. Will the HEI Dist. make any difference on the type of timing light needed to be used?

 

[Jim Hannon]

Had a fuel pressure guage on and when I turn key on I get an immediate 42psi and then it drops 10psi after pump goes off to 30psi in less than a second. It zeros out within 5 to 10 seconds. Have not ohm them out yet because I was thinking the injectors shouldnt be doing this. Is this correct? If so should I replace all the injectors or just ohm them out and replace the bad ones? Also noticed that the injectors are Ford injectors part # 181 280 150 556 or # FOTED5B thats all the numbers off the injectors. Do you know the correct injectors that are supposed to be in a 1986 corvette?

 

[vetteboy86]

A new set of injectors should be in your near future. Stock injectors for an 86 flowed 22 lb/hr. There are many good sources for injectors. I'm sure folks will chime in with their successes with injector purchases.

 

[FForward]

If the injectors are bad or going bad contact Jon Banner at Fuel Injection Connection and he will get you a set that will work great. I have an '89 and I changed over to Bosch Gen III's and what a difference they made. I don't think the injectors would cause eratic timing though. Make sure plug wires #5 & #7 are seperated from each other. Good luck!

 

[TedC]

If the injectors are bad or going bad contact Jon Banner at Fuel Injection Connection and he will get you a set that will work great. I have an '89 and I changed over to Bosch Gen III's and what a difference they made. I don't think the injectors would cause eratic timing though. Make sure plug wires #5 & #7 are seperated from each other. Good luck!

I agree with getting Bosch IIIs from Jon. I think Boom nailed this in his first post on cause and effect. So what is really causing the fuel pressure to drop? Leaking injectors would be the most likely cause. However, a defective check valve or defective fuel pressure regulator can cause this as well. My 1988 L98 had leaking injectors that caused a hard start condition when hot and they didn't indicate FP drops as large as those posted by Jim. Looks like a pretty big internal FP leak.

 

[boomdriver]

The regulator can leak in a couple ways...the diaphram can leak from a tear or split, and thats obvious by the fuel in the vac line. If the inj and pump all check out ok, the regulator plunger that contacts the seat can leak past and send pressure directly to the return side of the rail into the return line. You';ll never see anything except some irregular pressure readings and some unstable engine performance.

In this case its most likely the common things, either the injctors themselves leaking down,
(should hold pressure for several hrs) or the regulator diaphram.

Pull the vac line to the regulator, and if thats dry, call Jon. Ohms testing the inj only tells you if the coils are strong enough to operate..it says nothing about the nozzles themselves.

 

[Jim Hannon]

Got fuel injectors on the way. Was trying the pinch test out of the FSM.
I did the first step it said to:

IGNITION "OFF" FOR 10 SECONDS.
IGNITION "ON"
BLOCK FUEL PRESSURE
LINE BY PINCHING FLEX
HOSE, PRESSURE
SHOULD HOLD.

And it did hold. It said to CHECK:
• LEAKING PUMP COUPLING
HOSE OR PULSATOR.
• FAULTY IN-TANK PUMP.

We are going to fix the Pulsator. My other question is during the pinch test the fuel pressure held a 38psi is that somthing that I should be concerned about? The reason I ask is the FSM states that fuel pressure should be, "WITH PUMP RUNNING SHOULD BE 280-325 kPa(40.5-47 psi)" I also have a Haynes manual that says 34psi to
39psi. Which one would you say is correct? Im was not for sure because of revisions. Thanks alot for all your help. By the way what exactly does the pulsator do?

 

[Jim Hannon]

New info on erratic spark problem. Decided to check spark with spark tester and noticed that at .035 the spark didnt seem to be very powerful. I decided to adjust the gap more on the tester to check the spark color and it made the plug wires short out all over the place. When I checked them before in the dark I saw nothing. When wires are hooked to the plug as normal no arcing is noticed. Anyone have this problem before? The wires were purchased from a friend and was supposed to be NEW. Getting new wires tomorrow. Have any ideas why this would only happen when the spark tester is on the wires and set at a bigger gap?

 

[TedC]

Jim,
Seems like we are fighting two different issues...
1. If you have a weak spark on one wire, then swap that wire with one that works. Does the problem move? If it moved, then we have a defective wire. If it remained, then we have an issue with the distributor. The coil used on the L98s is a very good coil and produces powerful sparks. Mine will arc across a spark plug tester even at the widest settings using stock AC Delco wires. I've never seen weak spark on just one cylinder at the distributor, so this is sounding like defective spark plug wires. Did you replace the spark plugs?
2. FP levels can drop for multiple reasons. Based on test you ran (pinching the return line), then this would indicate a leak between the FPR and the fuel pump, not the injectors. This doesn't prove that the injectors are good, it just means that this major leak is coming from another source.

 

[boomdriver]

New info on erratic spark problem. Decided to check spark with spark tester and noticed that at .035 the spark didnt seem to be very powerful. I decided to adjust the gap more on the tester to check the spark color and it made the plug wires short out all over the place. When I checked them before in the dark I saw nothing. When wires are hooked to the plug as normal no arcing is noticed. Anyone have this problem before? The wires were purchased from a friend and was supposed to be NEW. Getting new wires tomorrow. Have any ideas why this would only happen when the spark tester is on the wires and set at a bigger gap?

Crappy wires...cheapo or wrong size will cause misfire so bad it won't run. Get NEW wires.. The C4 likes DELCO...not ChEAPO. Always use DELCO ignition parts.

The fuel...pumps probably getting tired. The pump has a check valve built in. That can cause the pressure to leak back into the tank. Try a new pump IF the pressure on the rails is not 40, and if the gauge needle flickers ANY while running the eng at a steady idle. The needle should be rock solid. Flickering indicates breaks in pressure....meaning a pump thats unable to maintain steady pressure. A leak in the line inside the tank is possible but TOO easy to see and correct.

Wires.
Pump.(tank gasket, new hose clamps, new screen)

problem solved.

 

[Jim Hannon]

New update got rid of miss and rich exhaust smell. Threw away timing light put in new injectors from injector connection timed by ear, now runs great. Noticed that the O/2 sensor are gone. How is the car running without pulling any codes?

 

[Jim Hannon]

I am not getting any codes. And the threaded holes for the o2 sensors are not there. Has the stock manifolds and y pipe but y pipe has been cut and new pipe welded to pipe and CAT. I dont know where o2 sensors are located on this system but was wondering if they go where the new section of pipe is. I have noticed unused plugs and wires under the car but am not sure what they are for. Should I try to put the sensors back on?

 

[TedC]

Well, if there is no O2 sensor, then the ECM can't switch to closed loop mode. You must be running in open loop all the time.

You should have one O2 sensor if it is like my 1989 on the driver's side.

 

[boomdriver]

Yep...

Teds right.

The o2 sensor is driver side just below the manifold/header collector near the oil filter. If you do not have one, somebody bubba'd the car somehow by deleting it. The ECM cannot possibly make the necessary adjustments to the fuel injectors or timing or anything without being able to shift to closed loop and use o2 sensor input. THAT is why you were running rich...your old injectors were likely worn out and needed to be replaced, but the open loop mode will cause it to get poor MPG, not perform as well as it could, and even cause premature wear from running rich.

Either someone blocked the SES lite by taking the bulb out, or MAYBE got the equip to alter the chip/tune to prevent it from coming on or shifting to CL, or they used an o2 simulator to provide a false signal to keep the ECM satisfied.

Whatever they did....I can assure you is illegal and/or half assed.
It will seem to run good in OPEN LOOP mode, but it CAN run better IF it can tune itself as it runs. The timing has a large window where the ECM can make it work if its close but again, its NOT RIGHT unless its "set" to spec.