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1990 Corvette fuel fouling number 1and 2 spark plugs only please Help!!

Crazyace909

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Joined
Oct 19, 2012
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16
Location
Clarksville, Tennessee
Corvette
1990 Bright Red Coupe Targa Top
This has been an ongoing problem with my vette since i got her. I have done all the normal tune up things (plugs, wires, cap, rotor etc) I have replaced the EGR valve with a new one and cleaned the passages as best I could with the EGR valve removed. I have replaced the Injectors also. Fuel pressure is about 40 to 43 psi not running I havent checked it running.
Here is the problem I am having right now and I am looking for some advice or a solution if anyone else has had this problem. I have combed hundreds of threads and cant find my problem anywhere.
My vette is running very rich it is fouling only number 1 and 2 spark plugs. When I put a timing light on on the wires there is a distinct misfire from the light the light will blink normally and then go blaank thenk light up go out random on number 1 and number 2. All the rest off the plugs fire correctly when I hook them up.
They are fuel fouled I will try to get a pic of them up if needed but I know for sure they are fuel fouled.
The man I got my vette from did not take care of her and I have been fixing alot of things to bring her back.
He told me that he had replaced the ECM on it with one that was from a Lumina or something and had to have it reprogrammed or something like that. I was wondering if that could be the culpret.
Any advice would be very appreciated I am just tired of throwing money at it and not fixing it.

Thanks a ton

Larry
 

G Winter

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2,177
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NW Iowa
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1990 red convert 6 sp
Sounds overly simple but make sure 1 and 2 wires aren't switched on the cap.
 

Schrade

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'90 LT 5
Sounds overly simple but make sure 1 and 2 wires aren't switched on the cap.

Mis-routed wires would do it...

Also, fouling could be leaking injectors.

You have to check the fuel pressure. Static pressure; motor off, including leakdown time.

Post back.
 

Crazyace909

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Joined
Oct 19, 2012
Messages
16
Location
Clarksville, Tennessee
Corvette
1990 Bright Red Coupe Targa Top
When I checked the static pressure the other day it was around 40 psi no leak down after 20 minuites thats why im not leaning towards injectors. I say that but it is always a 8 to 10 second cold start every morning like there is a leak from an injector and filling my cylinders. How long should I leave the pressure guagge on it for the leak down test. I checked the wires and they are all correct but I will double and triple check myself tomorrow since I know how easy it is to switch wires.
 

WHEELS 81

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Oct 15, 2012
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Location
NEW YORK
Corvette
1981,MAROON COUPE
Fouled plugs

When I checked the static pressure the other day it was around 40 psi no leak down after 20 minuites thats why im not leaning towards injectors. I say that but it is always a 8 to 10 second cold start every morning like there is a leak from an injector and filling my cylinders. How long should I leave the pressure guagge on it for the leak down test. I checked the wires and they are all correct but I will double and triple check myself tomorrow since I know how easy it is to switch wires.

If I remember correctly the firing order off the distributor cap is 1,8,4,3,6,5,7,2. So try switching wires 8 for 1, and 7 for 2 and see what happens. If 1 &2 foul up now the only thing that didnt change was the plugs, and and distributor. So you have eliminated the wires . A visual inspection of distributor cap and ohm meter should tell you if cap is A-ok. Plugs you can swop out with a known good one and see if they fire. Good luck
 
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Crazyace909

Member
Joined
Oct 19, 2012
Messages
16
Location
Clarksville, Tennessee
Corvette
1990 Bright Red Coupe Targa Top
If I remember correctly the firing order off the distributor cap is 1,8,4,3,6,5,7,2. So try switching wires 8 for 1, and 7 for 2 and see what happens. If 1 &2 foul up now the only thing that didnt change was the plugs, and and distributor. So you have eliminated the wires . A visual inspection of distributor cap and ohm meter should tell you if cap is A-ok. Plugs you can swop out with a known good one and see if they fire. Good luck

Switched the wires out and checked the distributor cap and components again this morning and all is good still misfire on 1 and 2 wires with the known good wires. Still causing a fuel fouling. I was reading that a bad oxygen sensor can cause the computer to be fooled and cause a rich condition but I would think this would show on more that just the first 2 plugs if this was the problem.

I have checked the codes and I am only getting a Code 32 which is EGR related. The one thiing that is confusing me is there is intermediant fire on 1 and 2 but all the other cylinders are firing correctly. could it be a bad pickup in the distributor?

The guy I bought my vette from said he put a new distributor in it i have replaced most of the components in it already except the pickups in it they visuaally look good any way to test them and see?
I did have to reset the timing when I got her because it was a notch off. I think im grasping for straws:r.
 

Schrade

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'90 LT 5
When I checked the static pressure the other day it was around 40 psi no leak down after 20 minuites thats why im not leaning towards injectors. I say that but it is always a 8 to 10 second cold start every morning like there is a leak from an injector and filling my cylinders. How long should I leave the pressure guagge on it for the leak down test. I checked the wires and they are all correct but I will double and triple check myself tomorrow since I know how easy it is to switch wires.

No leakdown for 20 minutes is good.

When warmed up, does it lope idle? Up and down RPMs?

Are the wires routed PROPERLY? IN THE WIRE LOOMS? If not, they WILL try to ground themselves out, especially the longer ones, like 1 and 2, with misfiring / fouling...
 
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Crazyace909

Member
Joined
Oct 19, 2012
Messages
16
Location
Clarksville, Tennessee
Corvette
1990 Bright Red Coupe Targa Top
No leakdown for 20 minutes is good.

When warmed up, does it lope idle? Up and down RPMs?

No lope just the miss. I can feel it in the steering wheel and it will burp or single miss bad ocassionally looking at the engine you can see the miss from the slight movement of the engine. With the timing light on the harmonic balancer my timing is very jumpy at times then it will be steady then jumpy again. Very confusing for me....:eyerole

I made sure they wires were all routed correctly and even did the dark room test to make sure I wasnt getting a misfire and none was present in the dark even at higher rpm's (revving).
 
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Crazyace909

Member
Joined
Oct 19, 2012
Messages
16
Location
Clarksville, Tennessee
Corvette
1990 Bright Red Coupe Targa Top
Here is what the spark plugs look like. 2012-10-20_09-27-50_338.jpg2012-10-20_09-28-15_385.jpg2012-10-20_09-27-57_398.jpg2012-10-20_09-28-39_398.jpg2012-10-20_09-28-45_893.jpg2012-10-20_09-28-49_670.jpg2012-10-20_09-28-57_561.jpg

Number 1 is on the right which looks better than number 2 on the left which looks completely fouled.
 

boomdriver

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Dec 18, 2008
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1,888
Location
texas
Corvette
87 z-51
Odd...
if you are SURE that its an intermittent spark, causing half the cyl cycles to be 'misfires' and thus fouling the plugs, then thats all it would take for me to go buy a new distributer.

Comp Sales recently had small cap HEI for sale for $88...complete.

Only other thing would be injector harness cross signalling. Since its across 2 banks, its likely not the wire but more the ECM inj driver circuit. If its dumping in TOO MUCH fuel from those 2 inj being told to stay open, that will foul the plug and cause it to mis but that will not make the spark signal mis a beat. Only the actual spark at the plug.The signal will be there..just no spark.

So, be certain of what you are seeing. Take the injector plug off #1 and swap it with #3. Does the problem move? If so, go find the CORRECT ECM instead of some bubba rig reprogrammed unit out of a Lumina...thats pure Bubba BS and should be suspect.

Did Luminas even have a V8????????????????????????????????????????????????????????????????
 

Crazyace909

Member
Joined
Oct 19, 2012
Messages
16
Location
Clarksville, Tennessee
Corvette
1990 Bright Red Coupe Targa Top
Odd...
if you are SURE that its an intermittent spark, causing half the cyl cycles to be 'misfires' and thus fouling the plugs, then thats all it would take for me to go buy a new distributer.

Comp Sales recently had small cap HEI for sale for $88...complete.

Only other thing would be injector harness cross signalling. Since its across 2 banks, its likely not the wire but more the ECM inj driver circuit. If its dumping in TOO MUCH fuel from those 2 inj being told to stay open, that will foul the plug and cause it to mis but that will not make the spark signal mis a beat. Only the actual spark at the plug.The signal will be there..just no spark.

So, be certain of what you are seeing. Take the injector plug off #1 and swap it with #3. Does the problem move? If so, go find the CORRECT ECM instead of some bubba rig reprogrammed unit out of a Lumina...thats pure Bubba BS and should be suspect.

Did Luminas even have a V8????????????????????????????????????????????????????????????????

Lumina's didnt have a V8 but the same computers were used in those and many other GM products throughout 1990 and 1993. I checked with the parts store and they have a remanned one for 99 dollars I am thinking about using it. Here is the link Cardone Remanufactured 77-7727 - Engine Control Computer | O'Reilly Auto Parts let me know what you think. If I swap the injector wires wouldnt that cause more missing since the computer would be confused or am I wrong? I just dont want to fry anything if I do that is all.

Im sure there is a misfire though i have even pulled the wire and watched the spark and it definately stops firing intermidentaley on 1 and 2.

Or mabye I should just replace the Ignition Pickup inside the distributor since thats the only thing i havent replaced on it. http://www.oreillyauto.com/site/c/d...4_1030&keyword=distributor+ignition+pickup#at I wish I could test the pickup to see if it was bad. Anyone got any idea on how to do that would be great.:D
 
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boomdriver

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87 z-51
moving the inj plug won;t hurt a thing. All that does is to ID the bad cyl as far as the fuel inj...the whole bank is the same circuit. Its called "bank-fired" where all 4 on that side fire together. If you did have a bad plug or bad section of wire to #1 that would move the problem to whatever inj it was resting on....
I have soldered in entire new sections of inj harness due to insulation rot and cross signalling/shorting. I had a misfire that I could not find...went thru the exact same things,. throwing parts, guessing. Finally moved some inj wires and the problem moved too...
New plugs can be bought, new wire can be soldered in the harness, IF that is the source of the problem.

So you watched a good plug misfire in that #1 or #2 spark plug wire? Are you 100% positive that the plug was clamped to something that provided a good solid ground? I've seen the same thing from a plug laying in the intake that misfired because it was vibrating with the engine...and breaking ground. Clamp it to something OR use an inline spark tester to SEE the spark with the plug installed.

HEI is hot enough to use that fouled plug in another cyl and I'd bet it burns clean after a few minutes. Those pics look more like oil fouling to me...too black for fuel.Whats the compression like in that bad cyl?

ICM are cheap $30...Don;t know about the pick-ups, but Like I said, the whole dist is cheap. The parts are far more costly than the unit as a whole... I kinda doubt its ICM, might be pick-ups..but thats reaching.
Get your FSM and start going thru the flow charts to the FSM conclusion. Thats never wrong.

I'm suspecious of that ECM....I do not like the idea of reprogramming something that was designed with specific intent. Besides, its the PROM that contains all the "tune" info...
 
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Crazyace909

Member
Joined
Oct 19, 2012
Messages
16
Location
Clarksville, Tennessee
Corvette
1990 Bright Red Coupe Targa Top
moving the inj plug won;t hurt a thing. All that does is to ID the bad cyl as far as the fuel inj...the whole bank is the same circuit. Its called "bank-fired" where all 4 on that side fire together. If you did have a bad plug or bad section of wire to #1 that would move the problem to whatever inj it was resting on....
I have soldered in entire new sections of inj harness due to insulation rot and cross signalling/shorting. I had a misfire that I could not find...went thru the exact same things,. throwing parts, guessing. Finally moved some inj wires and the problem moved too...
New plugs can be bought, new wire can be soldered in the harness, IF that is the source of the problem.

ICM is cheap...Don;t know about the pick-ups, but Like I said, the whole dist is cheap. The parts are far more costly that the unit as a whole... I kinda doubt its ICM, might be pick-ups..but thats reaching.
Get your FSM and start going thru the flow charts to the FSM conclusion. Thats never wrong.


Im going to go get a couple of new plugs first and I will check the Inj wire switch and let you know wwhat I come up with (fingers crossed thats the problem). If the injector wire is the problem would that cause my spark to disapear on those cylinders though? just thinking to much mabye.:eyerole

Update: Moved the injector plugs with no change. Put 2 differeent plugs in the 1 and 2 spots and started fouling them after 5 minuites of running they were already showing black soot on them. Exaust fumes were very rich also.

Decided to pull the distributor and check it out. pulled it apart and the pickips on the shaft had been damaged or it looks like that to me not on all off them just 2 were flattened some and notched on the end of them. I am going to get another distributor and change them out to eliminate that is the problem I will update again after this is done.

Thanks for all the good info so far I dont feel so lost now.:)
 
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Schrade

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'90 LT 5
Missing a tooth on the distributor drive?

Rotate the crank to 0 (or whatever 'fire' is for 1) with a breaker bar and a socket. See if there's play in the rotor at that point.

Actually, if a tooth is missing on the drive, and 1 and 2, which fire in sequence, then go to the fire degree for 1, and rotate the crank BACKwards halfway to 2, which is about half of 90 degrees - 45.
 

Crazyace909

Member
Joined
Oct 19, 2012
Messages
16
Location
Clarksville, Tennessee
Corvette
1990 Bright Red Coupe Targa Top
UPDATE: Ok after a long day of changing to distributor and then decided to change the ECM with a known good one from a buddy did all of that to no prevail. Still the same thing running rich and fouling the plugs. The one thing that did change is I did get rid of the misfire on 1 and 2 by changing the distributor sso that problem is solved.

After sitting for awhile and a few choice words I decided to go back through all that I had done to make sure everything was right. The first thing I fixed on my Vette was changing the injectors. So for shits and giggles I decided to check them. Low and behold the number 1 injector was only Ohming at 2.7 Ohms. I thought surely not it must be my meter so I checked number 3 and it checked out at 17.2 Ohms so its not my meter.
Long story short I checked all injectors and all of the read 17.0 Ohms plus except 1 and 2 which were 2.7 Ohms and 2.6 Ohms:mad. I was so mad at myself for not doing what I know should have been done to begin with which is check everything even if it is new because you never know when you are going to get a bad part.

I am going to takle the front 2 injectors tomorrow since I had 2 spare good ones in the garage. Hopefully this is my problem and I can end this thread on a good note.

I thank you all for the great advice and all the knowledge combined here is a great asset for all of us.

I will update again tomorrow after I finish the injectors.
 

Crazyace909

Member
Joined
Oct 19, 2012
Messages
16
Location
Clarksville, Tennessee
Corvette
1990 Bright Red Coupe Targa Top
Missing a tooth on the distributor drive?

Rotate the crank to 0 (or whatever 'fire' is for 1) with a breaker bar and a socket. See if there's play in the rotor at that point.

Actually, if a tooth is missing on the drive, and 1 and 2, which fire in sequence, then go to the fire degree for 1, and rotate the crank BACKwards halfway to 2, which is about half of 90 degrees - 45.

Not on the drive it was on the pickups inside the Pickup coil. The ones on the top of the shaft not the ones for the cam.
 

Schrade

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'90 LT 5
Your rear end is wrong for '90. Front end is correct...
 

Schrade

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'90 LT 5
LOL you are correct it was done before I got the car...:D

My '90 is wrong too - in reverse!

Front end is for '91 - '96, rear is correct (ONLY for ZR1, for '90 model). Very few catch that!!!
 

Crazyace909

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Joined
Oct 19, 2012
Messages
16
Location
Clarksville, Tennessee
Corvette
1990 Bright Red Coupe Targa Top
Finally FIXED!!!!!!!!

:vGot up bright and early this morning and replaced number 1 and number 2 injectors cleaned everything up put new plenium gaskets on it put it all back together.

Fired it up and cleared everything out rechecked timing and took it for a ride. Ran the best is has since I have had her.

Its Amazing how things go right when I did what I should have done to begin with.

Pulled the number 1 and 2 spark plugs and after the 10 mile run they were cleaned up and white again.....W:happyanim::happyanim:OOOO HOOOOO :happyanim::happyanim:problem solved.

Thanks to all who helped me out this forum is the best asset out there.

When we all combine our knowledge we can do anything.

:thanks:Thanks again

Larry:beer
 

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