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Old 07-28-2018, 12:29 PM
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94 Buick RoadMaster Estate Wagon LT1/ TPI question

Originally I posted this in transmission as I thought thatís what was going on.

However Iím almost certain this is a EFI issue or Optispark issue.

When cruising or light load at 55-70 mph the car shudders. I carefully noted what us going on. I have to press harder on the gas pedal to maintain speed and now it appears to be guzzling gas. On a full tank it has used more than 1/4 on the gage and only hone 140 miles, mostly highway. Yet the car idles dead smooth and drives around town very nicely. I tried shifting to 3rd gear and yes the motor speeds up. However it does shudder but less. The wagon has a towing package which includes a 2.92 or 3.08 rear end. I donít have any way to get under the car to check for rear end tags.

The 94 has the sequential fire port injectors. The last tank it got 21.8 mpg. I had a fuel pump, sending unit with cord, and fuel filter installed after the fuel,pump quit. The car starts and runs great except at highway speeds. The car only has 110k miles and has not seen a winter.

I know there are tests that can be done. None of the local auto parts stores have OBD 1 scanners. I know you can read codes through the AC panel but I donít know how to access this.

Looking into the Optispark I see that it can have issues in this speed range. Ultimately it looks like a replacement is coming, however I would like to be sure before throwing parts at it.

There is no tach on this year so I canít really see rpm. Itís so quiet that itís hard to hear the motor run.

Can anyone show some light on this.?
Feel free to ask more questions.

Byron

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Old 07-28-2018, 12:48 PM
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I have read in more than one place that a new set of spark plugs and quality wires can fix the problem, even though no codes are being thrown. Is it maybe time for a tune-up anyway?
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Old 07-28-2018, 01:38 PM
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This is a new system to,me so just getting plugs and new wires is an issue. Wires are not the easiest to get at this with the front mounted Optispark. Even the plugs are well hidden by all the stuff on top of the motor. I’m going down to the garage and take a better look.

Byron
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Old 07-28-2018, 02:19 PM
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The plugs are best accessed through the wheel wells. Sometimes the A.I.R. pump tubing is in the way (pass side). Routing the wires through the acessory brackets on the pass. side is a pain too.

link to video for climate control diagnostics:

You could also check here: 4th Gen LT1 F-Body Tech Aids for some help with troubleshooting.

Random sputter/missfire/shudder issues can be a pain to diagnose on these cars, dealing with a similar problem on my '95 right now...
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Old 07-28-2018, 02:19 PM
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double post - disregard pls
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Old 07-28-2018, 03:35 PM
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Nice video thanks. I also watched a factory video but they use a tester that probably costs more than a new Optispark does installed. Good info nevertheless less.

I just looked up spark plugs and wires. Of course these cars take the fancy rare metal construction plugs. Wires go upwards of $100 for the premium sets.

Iíll do a couple tests first and see if it is something easy. They talk about replacing the cap and rotor however you canít even see the cap without taking a bunch of stuff off the car first. Let alone get at it. So much for fancy cars.

Iím missing the Willys already. Other than ignition issues I never really had any problems fixing anything on that car. Maybe the mfg should just assign say five engineers and one machinist to build cars. That way we would get serviceable cars. Ha ha. The UAW would immediately strike.LOL

Byron
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Old 07-28-2018, 05:18 PM
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with any luck it is something easy like the ignition control module/wires/plugs.
the cap and rotor aren't too bad to get to. water pump and balancer need to come off, best to mark the balancer for reinstall since it is not keyed (there is an indexing mark on the back side of the crank hub). you'll want an E4 external torx to remove the cap or you can pull one of the torx bolts from the plate above the throttle body and use it.
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Old 07-29-2018, 09:49 AM
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Thanks for the additional info. I’m going to get plugs and wires this week. That will be the first step. I’ll call the repair shop I just had the fuel,pump done at and see if they can scan OBD 1. Meantime I’ll try the AC control test today just to see how it works and note any codes that show up.

I have to go get the el Camino sometime today so I’ll look at the Buick later.

Byron
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Old 07-29-2018, 03:47 PM
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Optispark

That's the early Optispark and it does not have the vacuum tube that later units have. With 110K on it I would say it's time to replace it. Have you been driving in the rain? Puddles? That will kill the Optispark quick. Does the water pump leak? If the pump is leaking a little it will seep into the Optispark too. I say replace the water pump, optispark, wires and plugs...it's time.
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Old 07-29-2018, 04:07 PM
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Quote:
Originally Posted by 39 master View Post
That's the early Optispark and it does not have the vacuum tube that later units have. With 110K on it I would say it's time to replace it. Have you been driving in the rain? Puddles? That will kill the Optispark quick. Does the water pump leak? If the pump is leaking a little it will seep into the Optispark too. I say replace the water pump, optispark, wires and plugs...it's time.
Yup ! The honeymoon's over !
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Old 07-29-2018, 05:08 PM
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94 & 95 B bodies got the vented opti. Wouldn't hurt to check that the vent tubes are hooked up and functional though.
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Old 07-29-2018, 07:15 PM
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Sounds like an injector problem

low rpm high engine load (top gear-s)

had it several times in the past.

Dump in some chevron techron ,like 2 bottles. Then drive normally .May have to dose it more than once. But dose it heavy the first time, see if it helps.
Or pull them and have them ultrasonic cleaned

Carbon build up on the backsides of the intake valves can cause this issue too. In tank injector cleaner addresses this issue also.
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Old 07-29-2018, 10:17 PM
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Well here in Minn rain and puddles are as common as snow and ice, so yeah it’s already been rained upon and been playing in puddles. I’m known for driving my classic cars and the semi classic Buick.

I thought about the injector cleaner as that was popular when EFI first came about. I always thought of it as snake oil but I’ll give it a try.

I got interrupted today so I didn’t get to check the car out for the vent line.

I guess it’s time for the 100k tune up.

Thanks for the tips.
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Old 07-30-2018, 11:23 AM
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Can the mods amend the title to LT1 instead of TPI? We know Byron has an LT1 but someone searching may not.

Be careful with your plastic wire-looms as they're supposed to be specific to the LT-series. Same with the wire length, traditional SB wires will make it into a project.

I had to finally put a "Petris" Opti on mine, with the vent added. But, I believe there are vented caps for the early opti available.
In this thread, there is a link to some diagnostics you can do to help pinpoint if its actually the opti crapping out on you. And lastly, make sure that your waterpump is leak free and (if it IS leaking) that the drive coupler for the waterpump isn't FUBAR. I'd suspect that many of the "these are junk" posts are related to lack of attention to detail.
https://www.corvetteforum.com/forums...pti-spark.html

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Old 07-30-2018, 02:41 PM
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Quote:
Originally Posted by bentwings View Post
Originally I posted this in transmission as I thought thatís what was going on.

However Iím almost certain this is a EFI issue or Optispark issue.

When cruising or light load at 55-70 mph the car shudders. I carefully noted what us going on. I have to press harder on the gas pedal to maintain speed and now it appears to be guzzling gas. On a full tank it has used more than 1/4 on the gage and only hone 140 miles, mostly highway. Yet the car idles dead smooth and drives around town very nicely. I tried shifting to 3rd gear and yes the motor speeds up. However it does shudder but less. The wagon has a towing package which includes a 2.92 or 3.08 rear end. I donít have any way to get under the car to check for rear end tags.

The 94 has the sequential fire port injectors. The last tank it got 21.8 mpg. I had a fuel pump, sending unit with cord, and fuel filter installed after the fuel,pump quit. The car starts and runs great except at highway speeds. The car only has 110k miles and has not seen a winter.

I know there are tests that can be done. None of the local auto parts stores have OBD 1 scanners. I know you can read codes through the AC panel but I donít know how to access this.

Looking into the Optispark I see that it can have issues in this speed range. Ultimately it looks like a replacement is coming, however I would like to be sure before throwing parts at it.

There is no tach on this year so I canít really see rpm. Itís so quiet that itís hard to hear the motor run.

Can anyone show some light on this.?
Feel free to ask more questions.

Byron
If this has Optispark then it is an LT1 engine by the year 1994. These are more OBD II than they are OBD I but are in fact someplace between so reading codes is questionable.

But, from your description the first thing that comes to mind is the transmission's 3/4 clutch or 2/4 band is going out.

Bogie
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