[sschevellefan]

So I changed the oil the other day on my 90 K5 blazer that is my daily driver with 228,000 miles. It was way over due but I finally did it. I put 20/50 in and everything seems fine, even gained a few psi on the freeway speeds. Anyway, after I changed the oil I started it and watched it get psi and shut it off. Checked the level and called it a night. The next morning it started running a little bogged down and the service engine light came on. I dropped off my kids and when I started it back up the light was gone and it was running fine. Then today I took the family to my home town and on the way there I stopped for gas and when i went to accelerate back onto the freeway it popped 3 times through the exhast and lacked power. I tried getting on it again and it bogged down a bit but then took off and was fine for the rest of the trip down there. On the way home I noticed that in high gear(700R4 trans) at around 60-65mph it would ping a bit on slight inclines and even got it to do it on flat grough. If I hit passing gear it was fine. I run 87 Arco gas and have never had a issue like this before. I`m sure it`s only a coincidence that it`s happening after I changed my oil but it has run like a top since I got it back in March. Does anyone have any ideas what would cause this? Wasn`t running hot at all and runs fine around town just pinpg on light throttle at freeway speeds in high gear. Could it be bad gas or something?

 

[Schurkey]

Might want to take a look at the distributor. The small-body HEI is known for having some issues in high-mileage situations. Mine ('88 4x4, well over 200,000 miles) needed a new distributor shaft; and it's my understanding that that's not uncommon.

The last one of these that had driveability problems (hard starting, no power, massive misfire) required nothing more than a new cap 'n' rotor (rotor wore out, augered out the carbon button in the center of the cap) and plug wires.

 

[sschevellefan]

you know, it is hard to start in the morning. I try to let the pump pressure up but it still cranks for a good 10-15 seconds before it starts unless it`s already up to temp. It also has a pretty good miss n the mornings too sometimes. I just replaced the plugs about a month ao but didn`t even think about the cap and rotor. It does need new wires though because a couple boots are torn and patched with black tape. Hopefully thats the problem. I love this thing and it`s never given me any issues and only slightly smokes on start up considering the miles it has. I`ll try the cap/rotor and wires and see how she runs. Thanks.

 

[BigBocks66SS]

If I remember right, the fuel pump circuit and oil pressure are tied together, in other words the truck won't start until there is enough oil pressure. You might try another oil sending unit which may help with your cold crank problem. I bought my 89 Silverado about 14 years ago, it had 87,000 mile on it, and smoked a little when I first started it in the morning, the only thing I've done different is use Chevron fuel with Techron, and it quit smoking, and to this day with 276,000 miles, it still doesn't smoke or use a drop of oil. I also use Castrol 20-50w in it and always have, and change the oil every 5000 miles, heck it even has the original fuel pump, master cylinder, freon in the a/c and original distributor. I've tuned it up twice, including plugs,wires & cap, rebuilt the starter 3 times, the alternator 2 times, on my 3rd water pump, and last year had to put new intake gaskets on it. But the truck has been a good one, and I drive it everyday 40 miles round trip to and from work.
Back to your truck, you definetly need to replace those plug wires, and cap. And the like someone else mentioned, the distributor shafts are bad to wear, so pull the distributor and check the shaft bushings, and maybe try a new oil sending unit. Another thing to check is the injectors, I have seen the screens in them get plugged up with debris. Pretty easy to remove them and check. Also about the Techron I mentioned, I think you can buy it as an additive without buying fuel from Chevron or Texaco.

 

[sschevellefan]

If I remember right, the fuel pump circuit and oil pressure are tied together, in other words the truck won't start until there is enough oil pressure. You might try another oil sending unit which may help with your cold crank problem. I bought my 89 Silverado about 14 years ago, it had 87,000 mile on it, and smoked a little when I first started it in the morning, the only thing I've done different is use Chevron fuel with Techron, and it quit smoking, and to this day with 276,000 miles, it still doesn't smoke or use a drop of oil. I also use Castrol 20-50w in it and always have, and change the oil every 5000 miles, heck it even has the original fuel pump, master cylinder, freon in the a/c and original distributor. I've tuned it up twice, including plugs,wires & cap, rebuilt the starter 3 times, the alternator 2 times, on my 3rd water pump, and last year had to put new intake gaskets on it. But the truck has been a good one, and I drive it everyday 40 miles round trip to and from work.
Back to your truck, you definetly need to replace those plug wires, and cap. And the like someone else mentioned, the distributor shafts are bad to wear, so pull the distributor and check the shaft bushings, and maybe try a new oil sending unit. Another thing to check is the injectors, I have seen the screens in them get plugged up with debris. Pretty easy to remove them and check. Also about the Techron I mentioned, I think you can buy it as an additive without buying fuel from Chevron or Texaco.

I don`t know if the circuts are tied together but once it`s warmed up it`s not a issue anymore. I`d like to hear more about how different gas will stop the smoking because from my experience smoke on start up is usually valve guides or seals. Mine doesn` t smoke alot on start up but a puff does come out. I`m going to get wires.cap/rotor asap and see how it runs. I`m not going to pull the dizzy just yet as it`smy only vehicle and I don`t have a timing light so I can`t afford to have this thing really running like crap. I have seen some billet distributors on ebay for like $75, anyone use one of those? We have a fuel system cleaner at work I`ve been wanting to do but haven`t had the time or money.

 

[Schurkey]

I have seen some billet distributors on ebay for like $75,

You are WAY, WAY better off with a "good used" or rebuilt Delco distributor than a brand-new Chinese knock-off distributor.

We have a fuel system cleaner at work I`ve been wanting to do but haven`t had the time or money.

My impression--and I could be wrong--is that there's not much point to cleaning a TBI; the injector holes that the gasoline sprays out of aren't so small that they tend to plug up or foul. I've never played with the "screens" inside; that may be a valid maintenance issue.


So far as I know, there's no tie between the oil pressure and the ignition that would prevent the engine from starting. That is, once the engine is running, it needs oil pressure to keep the fuel pump relay engaged--but--the relay is also energized for a couple of seconds when you turn the key to "run"; and the engine will start on that amount of fuel.

The oil pressure sending unit--for the factory gauge--is a known problem. I've needed to replace it twice on my truck; and I don't know if the thing was original when I bought it. The typical symptom is the gauge reads lower than you'd expect, and when you unscrew the sending unit to put a mechanical "shop gauge" on it to verify pressure--the sending unit is heavier than heck and sloshes as you move it around. It's nearly full of oil that's gotten past the seal; and the internal "guts" can't register pressure correctly.

Neither of my sending units have had external leaks when the inside got filled with oil. They've filled slowly enough that the oil pressure "drop" wasn't really something that stood out.

The last time I changed sending units, I "gained" about 20--25 psi at idle.

 

[rkd]

Not sure if this is much help, but I would scan it an pull the codes before changing any parts, unless something obvious has failed.

Even these obd1 puters can be helpful.

 

[sschevellefan]

I checked this morning and it fired up before the gauge read any psi so I don`t think they are connected at all. I normaly have 30psi just about all the time but now while on the freeway it goes to 35-40psi or so. It`s never been less than 30psi though. I don`t plan to change the distributor but I will change the cap rotor and wires and see what happens. It`s never given me any issues so I`m starting to worrie a bit since i don`t have the money to replace anything expencive right now. I`ll check the codes but the fact that the light went out tells me that whatever happend cleared it`s self up. If it was something serious it would still be on.

 

[SWHEATON]

If you have a bad/crakced cap or bad rotor or any plug wires are bad that can also partially foul the plugs too even if they arent that old so replace them at the same time or at the very least check to ensure none are fouled-dirty and if so then replace them.

Bad coil ,ign module,or bad fuel could cause same issues too.

Scott

 

[sschevellefan]

Just wanted to give a update. I replaced the cap/rotor and plug wires and the problem is gone and the engine light stays off. I noticed that the light would come on when the truck got up to temp at first but then it just stayed on. I guess one of the parts was breaking down when it got up to temp and then finally gave up. It runs great now with no other issues. I`m pretty sure I need a new TP sensor or a adjustment if they are adjustable because of the hard starting in the morning and the occasinal surge at idle and I`m going to replace the valve seals to stop the light smoke on start up and keep driving it untill i can afford to build a replacment engine or just buy a new Gm crate. Thanks for the input guys.

 

[richietables]

Thanks for the update. 228K is nothing to sneeze at, so whatever it takes, you know? Good luck with it.