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Topic: TuneUp Time

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TuneUp Time (1/9)
 12/17/13 8:12pm
cco
Former Member

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Joined: 8/16/2013
Posts: 191

Spring is tune up time for my recent C4 addition. 1994 LT1 auto rag with 25k miles.

I understand that ignition timing isn't normally adjustable, so it's down to plugs, wires, cap maybe coil(s).........

It has the replacement opti-spark already so that's out of the way.

Can the distributor be serviced without removing the pump?

Other than the engine inlet air filter, are there any other filters that might need servicing?

Thanks for any help.

Colin.
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Re: TuneUp Time (2/9)
 12/18/13 12:25pm
396c4
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Joined: 12/7/2011
Posts: 219

OEM Opti? MSD does have an external adjustment but you will get an MIL if you go much and you don't really have a TDC reference unless you take the time to add one and degree the damper ( which isn't keyed so could move) or digital timing light to compensate. You should check the vacuum hose from the Opti to make sure it's pulling air. Water pump does need to come off among most everything else to get at it. The screws holding the cover are practically un-removeable unless you do it properly and the O-rings make it equally difficult to replace. I switched to hex type when I get them out instead of the philps it comes with. Rotor and cap should be OK at 25 K though.

Check all the vacuum hoses. I changed the cruise control hoses years ago because they made your hands black just touching them so were due to crack. I used some silicone replacements because they stay more flexible and seal better. Probably could use a serpentine belt too. It will likely show cracks and chunks missing on the grooved side.

You might want to change the PCV and clean your EGR. There is a link in one of the posts that goes through it thoroughly. Injector cleaner? I dump a bottle of STP cleaner in the tank at the oil change.

Unfortunately, we don't have cabin filters. Wiper blades are likely due. BTW the reflex type are all too tall and difficult to find just replacement blades. I bought the whole assembly to strip the blades and mount on my OEM arms.

What mileage are you at? Tranny fluid and rear end fluid might be on the list. I've put Royal Purple synthetic in both. Should be a little performance there as well although the peace of mind is worth at least as much.

Have you looked at your rubber suspension bushings? From shocks to control arms, you might be in for a surprise unless it already has urethane conversion.

What about coolant? Supposed to be changed every couple of years although most people don't. You are supposed to add the pellets with the coolant because of the aluminum in the motor but I like water wetter better. To drain it properly, I pull the knock sensor on the side of the block. You can have it flushed obviously. Might be the time to do a thermostat although I won't get into the controversy about the temp but I do run a 180.

If you want to get really serious, look at the random misfire index. I've come to find out, if the engine isn't misfiring, the misfire index will tell you if the timing chain is going or gone. Index will be around 800 when all is well, otherwise .... eventually you will get an MIL for random misfire that can't be fixed with tune-up stuff.

O2 Sensors have a life! They will drift even if they appear to be functioning. The ones in front of the cats in particular since that's the signal for the closed loop tuning.

Good hunting!


|UPDATED|12/18/2013 9:25:45 AM (AZT)|/UPDATED|


______________
Re: TuneUp Time (3/9)
 12/18/13 3:20pm
cco
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Joined: 8/16/2013
Posts: 191


Wow that's quite a comprehensive reply there John, and very much appreciated. Some of the things you mentioned I did forget and others I knew nothing about.

The Opti was done by the original owner at the dealership (I have the records) -- I won't worry about timing adjustment for the few ponies one can get from it. The vacuum hose I'll have a look at and the cruise control vac hose was off when I got the car. Seems ok now but will look for a silicone replacement for longevity.

Likewise I'll check the serpentine -- have replacement from trip back from BC to Ontario JIC.

PVC and EGR didn't occur to me. So now they're on the list.

Injector cleaner -- I use Chevron's Techron in my other vette so it'll go in the C4.

Wiper blades - check.

Didn't even consider the suspension bushings. -- On the list to change to urethane.

Coolant gravity seemed ok and I added Water Wetter as I do in all my cars. If there's any doubt on the coolan's age I'll change it out. The thermostat I did do after getting it home in an attempt to make it run cooler. It's also a 180*.

"Random Misfire Index" sound intriguing -- Is that done with an OBD scanner or is there another way?  I don't have an OBD-1 scanner.

Forward O2 sensors are worth looking at to see how gummed up they are. On the list.

Once again John -- thanks so much for taking the time to reply. Very much obliged. I'm looking

forward to many miles next summer on the C4. She's a different beast than my GS and in some ways I like her more because of it.

Cheers,
 Colin. -- in Cambridge, Ontario, Canada.








396c4 said:
OEM Opti? MSD does have an external adjustment but you will get an MIL if you go much and you don't really have a TDC reference unless you take the time to add one and degree the damper ( which isn't keyed so could move) or digital timing light to compensate. You should check the vacuum hose from the Opti to make sure it's pulling air. Water pump does need to come off among most everything else to get at it. The screws holding the cover are practically un-removeable unless you do it properly and the O-rings make it equally difficult to replace. I switched to hex type when I get them out instead of the phillips it comes with. Rotor and cap should be OK at 25 K though.

Check all the vacuum hoses. I changed the cruise control hoses years ago because they made your hands black just touching them so were due to crack. I used some silicone replacements because they stay more flexible and seal better. Probably could use a serpentine belt too. It will likely show cracks and chunks missing on the grooved side.

You might want to change the PCV and clean your EGR. There is a link in one of the posts that goes through it thoroughly. Injector cleaner? I dump a bottle of STP cleaner in the tank at the oil change.

Unfortunately, we don't have cabin filters. Wiper blades are likely due. BTW the reflex type are all too tall and difficult to find just replacement blades. I bought the whole assembly to strip the blades and mount on my OEM arms.

What mileage are you at? Tranny fluid and rear end fluid might be on the list. I've put Royal Purple synthetic in both. Should be a little performance there as well although the peace of mind is worth at least as much.

Have you looked at your rubber suspension bushings? From shocks to control arms, you might be in for a surprise unless it already has urethane conversion.

What about coolant? Supposed to be changed every couple of years although most people don't. You are supposed to add the pellets with the coolant because of the aluminum in the motor but I like water wetter better. To drain it properly, I pull the knock sensor on the side of the block. You can have it flushed obviously. Might be the time to do a thermostat although I won't get into the controversy about the temp but I do run a 180.

If you want to get really serious, look at the random misfire index. I've come to find out, if the engine isn't misfiring, the misfire index will tell you if the timing chain is going or gone. Index will be around 800 when all is well, otherwise .... eventually you will get an MIL for random misfire that can't be fixed with tune-up stuff.

O2 Sensors have a life! They will drift even if they appear to be functioning. The ones in front of the cats in particular since that's the signal for the closed loop tuning.

Good hunting!














|UPDATED|12/18/2013 12:20:47 PM (AZT)|/UPDATED|
Re: TuneUp Time (4/9)
 12/19/13 9:58pm
396c4
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Joined: 12/7/2011
Posts: 219

The "misfire index" is OBDII and you will need a scanner or something like Autotap. Your O2 sensors are due based on age alone even if they work and don't appear to be too bad, they will drift out of calibration and change your tune-up. You can't really tell at the tailpipe either because if your cats are working, they mask the operating point.

One more thing. Your tires are well past their useable life. They might look OK for a static display but not for driving speeds or spirited(Wink) driving. Been well documented they can be an accident waiting to happen. If you take durometer readings, I bet you'll find they are much harder than new ones. My Pilot Sports run around 75 durometer but M/T Streets are down around 45 (new).

Brake fluid is supposed to be changed every few years too. There is a moisture contamination buildup and copper transfer from the lines. Test kits are available to check but it's not expensive to change. The first time I purged mine, switched to ss braided lines, I found a noticeable difference in the pedal. I used one of the tank type pressure feeders to do it alone with the check valve bleeders. I can recommend Crowne brake lines. I had them do a set for me in custom length to go with the lowered stance and extended travel and been very happy with the quality and service.


______________
Re: TuneUp Time (5/9)
 12/20/13 2:51pm
cco
Former Member

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Joined: 8/16/2013
Posts: 191

396c4 said: The "misfire index" is OBDII and you will need a scanner or something like Autotap. Your O2 sensors are due based on age alone even if they work and don't appear to be too bad, they will drift out of calibration and change your tune-up. You can't really tell at the tailpipe either because if your cats are working, they mask the operating point.

One more thing. Your tires are well past their useable life. They might look OK for a static display but not for driving speeds or spirited(Wink) driving. Been well documented they can be an accident waiting to happen. If you take durometer readings, I bet you'll find they are much harder than new ones. My Pilot Sports run around 75 durometer but M/T Streets are down around 45 (new).

Brake fluid is supposed to be changed every few years too. There is a moisture contamination buildup and copper transfer from the lines. Test kits are available to check but it's not expensive to change. The first time I purged mine, switched to ss braided lines, I found a noticeable difference in the pedal. I used one of the tank type pressure feeders to do it alone with the check valve bleeders. I can recommend Crowne brake lines. I had them do a set for me in custom length to go with the lowered stance and extended travel and been very happy with the quality and service.


That will be a few more things for the list -- O2's, tires, brake fluid and Crowne ss lines.

Yes the tires are '04 's tho  looking new, they are old and should be replaced.

I do have an OBD-2 scanner (an Innova 3110) -- Would that scan for misfires?

I thought '94 was the last year for OBD-1 ..... not sure.

Many thanks once again John -- you've been a big help.

Cheers,
 Colin.
Re: TuneUp Time (6/9)
 12/20/13 4:11pm
CaledoniaBrian
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, - Canada

Vette(s):
1988 Convertable


Joined: 11/3/2011
Posts: 150

For all practical purposes the 94 is a OBD 1 system. But it does use the OBD2 ALDL connector. A OBD2 code reader will not work if you hook it up.

Even though the system is an OBD1, it has some imbedded OBD2 codes but you need something like a tech1 to read them and then I don’t know how beneficial it would be any way.

I would just forget about the OBD2 for the 94 and make life simple. You will be very hard pressed to find a OBD1 code reader with the OBD2 connector, but they are around. But on the brighter side, the on board diagnosis to get the codes works very well and will give you more information than most ordinary code readers. Like the CCM codes and EBTCM (brake) codes. Learn how to use the on board well and you will be doing good.


______________

Re: TuneUp Time (7/9)
 12/20/13 4:38pm
cco
Former Member

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Joined: 8/16/2013
Posts: 191

CaledoniaBrian said: For all practical purposes the 94 is a OBD 1 system. But it does use the OBD2 ALDL connector. A OBD2 code reader will not work if you hook it up.

Even though the system is an OBD1, it has some imbedded OBD2 codes but you need something like a tech1 to read them and then I don’t know how beneficial it would be any way.

I would just forget about the OBD2 for the 94 and make life simple. You will be very hard pressed to find a OBD1 code reader with the OBD2 connector, but they are around. But on the brighter side, the on board diagnosis to get the codes works very well and will give you more information than most ordinary code readers. Like the CCM codes and EBTCM (brake) codes. Learn how to use the on board well and you will be doing good.



Thanks Brian -- I did read up on displaying codes and indeed tried the other day while warming the car. Works neat
 and I liked it. Quite the feature. I got a pile of numbers out of the memory but didn't write them down ..
Spring time for that.

Here's the link for the procedure should anyone need it. Hope it's not breaking any rules:

http://forums.corvetteforum.com/c4-tech-performance/3387421-my-vats-problems-persist-2.html

Cheers,
 C.
Re: TuneUp Time (8/9)
 12/21/13 1:19pm
davep85c4
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Joined: 4/4/2009
Posts: 254

How about Fuel Filter? Not mentioned so far.

|UPDATED|12/21/2013 10:19:49 AM (AZT)|/UPDATED|
Re: TuneUp Time (9/9)
 12/21/13 3:37pm
cco
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Joined: 8/16/2013
Posts: 191

DaveP85C4 said: How about Fuel Filter? Not mentioned so far.




Yes Dave, must not forget the fuel filter.
Thanks.
 C.
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