91 350 TBI Engine maintenance.

[Ds9Defiant1701]

Hi,

I just bought a 91 350 TBI with 267K km and i was thinking about doing the spark plugs, Wires etc. Maybe even distributor and other stuff. Its my first GMT400 and i love it so far.

First what kind of cable/Plugs i should use? Does high performance and iridium plugs help for power?

Is it worth changing the distributor if the engine runs well? Does it need to be retimed if i change it.

Any other preventive/Needed maintenance i should do on the engine or tranny?

Thanks for your help

 

[Erik the Awful]

First what kind of cable/Plugs i should use? Does high performance and iridium plugs help for power?

Use quality spark plug wires. Ideally you want 8mm wire or better. Fortunately our trucks are so common that you can get quality wires dirt cheap. https://www.rockauto.com/en/moreinfo.php?pk=871633&cc=1031230&jsn=528&jsn=528

As far as spark plugs, don't fall for the funky plug of the day. Plugs can do nothing for power except ruin it. Use the AC Delco plug that was designed for your truck, not the "Brand X Super Power Iridicardomom Split Prong Racing Plug". True story, when I was a Nissan technician, Champion was trying to corner the spark plug market and selling their platinum plugs dirt cheap. Every time we had a Nissan come in with a misfire we'd check the plugs first, and 90% of the time they had the Champion plugs in them. Use AC Delcos for your truck. https://www.rockauto.com/en/moreinfo.php?pk=89965&cc=1031230&jsn=536

Here's your cheat sheet for which plug brand to buy based on the type of vehicle:
GM - AC Delco
Ford - Autolite
Chrysler - Champion
Japanese - NGK or Nippondenso
German - Bosch

Note that NGKs also seem to do well in GMs.

Is it worth changing the distributor if the engine runs well?

If it ain't broke, don't fix it.

Any other preventive/Needed maintenance i should do on the engine or tranny?

267k km? Oh, you're one of those types. Metric commies! J/k, at 166k miles you're not too far along to do a transmission fluid and filter change. Don't buy a "transmission flush", just drain the pan, replace the filter, and refill the transmission. Most of your existing fluid will stay in, but that's okay. Some guys swear you absolutely need to change all the fluid, others of us have seen trannys poo the bed after a full flush.

I'd be more worried about changing the coolant. It gets corrosive over time, and yours has had 30 years if it hasn't been changed.

 

[Ds9Defiant1701]

Use quality spark plug wires. Ideally you want 8mm wire or better. Fortunately our trucks are so common that you can get quality wires dirt cheap. https://www.rockauto.com/en/moreinfo.php?pk=871633&cc=1031230&jsn=528&jsn=528

As far as spark plugs, don't fall for the funky plug of the day. Plugs can do nothing for power except ruin it. Use the AC Delco plug that was designed for your truck, not the "Brand X Super Power Iridicardomom Split Prong Racing Plug". True story, when I was a Nissan technician, Champion was trying to corner the spark plug market and selling their platinum plugs dirt cheap. Every time we had a Nissan come in with a misfire we'd check the plugs first, and 90% of the time they had the Champion plugs in them. Use AC Delcos for your truck. https://www.rockauto.com/en/moreinfo.php?pk=89965&cc=1031230&jsn=536

Here's your cheat sheet for which plug brand to buy based on the type of vehicle:
GM - AC Delco
Ford - Autolite
Chrysler - Champion
Japanese - NGK or Nippondenso
German - Bosch

Note that NGKs also seem to do well in GMs.


If it ain't broke, don't fix it.


267k km? Oh, you're one of those types. Metric commies! J/k, at 166k miles you're not too far along to do a transmission fluid and filter change. Don't buy a "transmission flush", just drain the pan, replace the filter, and refill the transmission. Most of your existing fluid will stay in, but that's okay. Some guys swear you absolutely need to change all the fluid, others of us have seen trannys poo the bed after a full flush.

I'd be more worried about changing the coolant. It gets corrosive over time, and yours has had 30 years if it hasn't been changed.

Well the coolant was kinda changing itself recently since i had a leak lmao and i think i still have one to find so i think on that part it will be okay lol

Yeah i found ACDelco near me for 4 bucks each so i'll return my NGK that i bought earlier.

Also i was told by few mechanics to not touch tranny fluid if you don't know when it was done.

 

[df2x4]

Also i was told by few mechanics to not touch tranny fluid if you don't know when it was done.

Personally I would not trust those mechanics.

A drain and fill with new filter like Erik described isn't going to hurt anything.

 

[Erik the Awful]

Also i was told by few mechanics to not touch tranny fluid if you don't know when it was done.

If your truck was over 300k km, I'd agree. I think you're good to do a filter change. If you don't do a filter change, start setting aside money each month for a transmission swap.

 

[DerekTheGreat]

I just got through putting new plugs, wires, cap, rotor and ICM on my truck. I changed out the coil for one pulled at a treasure yard years ago. Despite all three of my coils testing out ok via the service manual's procedure, I still think the one on my truck was causing my jumpy tach when cold started. Doesn't do that any more.

I used United Motor Products everywhere- Don't trust AC Smelco stuff any more, especially their plugs now that they're made in China.

Here's what I used:

Dizzy Cap: DC-840X
Dizzy Rotor: DR-840
Wire Set: 8858
Plugs: NGK 2771's
ICM: M-1990

Ordered all stuff through Rock Auto.

Only thing I don't like is that the spark plug wires are all a bit longer than they need to be. Seems every kit I've ever put on a small block is that way though. So there's a slight spaghetti mess behind the dizzy in order for them to look neat everywhere else.

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Runs smoother than it ever has, especially at idle. Also seems like it has more power when starting off in 1st, like it's not as easy to stall it. Used to run smooth at times at idle, but was typically choppy.

 

[Ds9Defiant1701]

If your truck was over 300k km, I'd agree. I think you're good to do a filter change. If you don't do a filter change, start setting aside money each month for a transmission swap.

How do i change the filter in those trans? I've never done anything like that before. Also i was thinking of modding my TBI to a carb head. Will i lose HP if i do that?

 

[PlayingWithTBI]

How do i change the filter in those trans?

Remove most of the rear trans pan bolts, prepare to get fluid all over the place, and loosen the rest of the front bolts until you can break the seal between the pan and body of the trans. A big catch pan will help. The filter is hanging below the valve body of the trans. Invest in a good filter and gasket that comes in a flat package rather than folded up in a small box. Replace and refill with Dexron VI (synthetic) ATF.

Also i was thinking of modding my TBI to a carb head.

Please don't go there! You'll lose timing control, AFR (Air Fuel Ratio) when temps and altitudes change, AND essential diagnostics code reading capability through the OBDI ALDL connector.

I know it sounds like witchcraft at 1st but, with some research and inexpensive diagnostic tools, you can figure it out on your own without ever (hopefully) having to take it in to a shop!

 

[Erik the Awful]

If your TBI is working, don't dork with it, and I say that without even liking TBI.

Replacing the transmission filter is just like PlayingWithTBI says. One important note! Make sure you get the old filter seal out of the transmission. They can be a real pain in the butt. The new filter just pops into place with no bolts to hold it. You'll be wondering how such a chintzy setup works, but it does.

When you add fluid back into the transmission (through the dipstick - you'll need a funnel) you'll want the engine warm and idling. Adding fluid with the engine off will give you a false reading. Add fluid, cycle it down through each gear and back into park, MAKE SURE IT'S IN PARK, then recheck the dipstick. Repeat until it reads good.

 

[Ds9Defiant1701]

Remove most of the rear trans pan bolts, prepare to get fluid all over the place, and loosen the rest of the front bolts until you can break the seal between the pan and body of the trans. A big catch pan will help. The filter is hanging below the valve body of the trans. Invest in a good filter and gasket that comes in a flat package rather than folded up in a small box. Replace and refill with Dexron VI (synthetic) ATF.


Please don't go there! You'll lose timing control, AFR (Air Fuel Ratio) when temps and altitudes change, AND essential diagnostics code reading capability through the OBDI ALDL connector.

I know it sounds like witchcraft at 1st but, with some research and inexpensive diagnostic tools, you can figure it out on your own without ever (hopefully) having to take it in to a shop!

Okay then is there any way to add some HP to the TBI?