84 K5 with a 6.2

[woodwright]

I recently picked up an 84 K5 with a 6.2. The PO had parked it some years back after getting some excessive coolant pressure. Long story short, I got it back together tonight and was trying to start it. It will almost start but then dies immediately when you let go of the key. And so far isn't showing any oil pressure. I didn't take the bottom end apart, as it only has about 20k on it. Do these older 6.2's with the mechanical lift pumps have an oil pressure kill switch? I also don't have any coolant in it as I was only gonna let it run for a minute.

How would I go about checking to see whether my oil pressure switch is bad, or my oil pump? I'm used to working on small block chevy's where you could pull the valve cover and see if you are getting oil up there. Thanks.

[DmaxMaverick]

It's likely your primary ignition circuit, fuse (ECM or IGN), or the ignition switch. The switch powers the pump like older gassers power a coil during cranking. There is no electrical interface with the mechanical fuel pump. The only "fuel control" on it is the ESS (Engine Stop Solenoid), on the injection pump (forward-most connector). Check for battery voltage at the ESS connector with key on. If it is trying to start while cranking, then fails after you release the key, you likely have an ignition power problem and air in the fuel system. Try applying 12V to the solenoid (jumper it from Batt+ to the solenoid), and purging the air. Get one problem fixed before going after the other.

[woodwright]

I did check the fuel solenoid. It comes on with the key. You mentioned air in the system, I just put the whole system back together so theres probably a little. Its weird though. It will start firing, and then instantly die when you let go of the key.

How do you check the oil pressure sending unit, and how can you visually check to see if oil is getting pumped around?

[DmaxMaverick]

Don't worry about the oil pressure, for now. If it's up to the mark, check the pressure after it starts. If it's been idle for a while, a start without oil pressure will have the lifters sounding off like a can of marbles. If after a start you still don't get oil pressure on the gage, you'll have to correct that, either by verifying pressure with a mechanical gage (recommended as a first step), and/or replacement of the sender, gage or wiring, as necessary. Make sure the sender connector is in good shape and secure. Oil pump failure is extremely rare, and hardly ever seen. Loss of oil pressure, when it does happen, is usually caused by another system failure, such as oil cooler lines, filter or internal bypass.

You may not have sufficient cranking speed. If less than 100 RPM's, starting is difficult. Add to that, other issues (like air in the fuel system), and starting is near impossible. Slow cranking will also delay oil pressure indication. Make sure your batteries are fully charged and providing full voltage, and the terminals/grounds are clean and tight. Limit your cranking cycles to 20 seconds or less, and allow a couple minutes between to prevent overheating the starter. If it sounds like it's trying to stumble into a start, it is getting fuel. Try adding a little throttle during cranking. If no change, then there is insufficient heat to fire off enough cylinders/fuel to run. Low cranking speed is low heat, even with well working glow plugs. Check the plugs and make sure they are working, as well. Trying to start may be a bit easier later in the day, before it cools off. A heat soaked engine will crank easier, and the additional heat helps with ignition.

[woodwright]

Little update on this thread, I got it running the next day, I think there was just air in the line. I want to run through what I've done so far, and get some feedback.

The PO parked the blazer 10 years ago due to getting excess coolant pressure. The bottom end only has about 20K, and the IP only has 5K. He told me the pump was turned up quite a bit, and rolls smoke under load. It also has 2 1/2" duels with flowmasters.

Anyway, when I got it, I didn't want to pull the whole motor, so I just pulled the heads to replace the head gaskets, and found cracks between the valves on cylinders 2,7, and 8. I had another crack free set, so I used those just in case. While I had it apart, I swapped in a J code manifold, and port matched the heads and manifolds. New fuel filter, and batteries, and tried starting it.

So now that's where this thread started. The day after I started it, I got the air bled out and got it running. When I went to put coolant into it, The radiator looked like it had been peppered with a shotgun, and a freeze plug was missing. So after all that, I pulled the motor anyway. I swapped out all the freeze plugs, the pan gasket, and the pump seals on the tranny. I replaced all the hoses, and installed new 60G glow plugs. Put the motor back in, and a rebuilt radiator, and back to square one. It runs really good, but is kind of a bear to start. I posted another thread about this, and I think its a mixture of old fuel and maybe a tired lift pump. I think there are a few bugs with the tranny, and I don't have the exhaust on, but it's running better and better. This is the first 6.2 I've ever driven so I don't know how it compares power wise, but it seems pretty peppy. I was once told that acceleration would be about like a throttle body 350, but I think we're better than that. Its deceiving with no exhaust, but it seems quicker than my last blazer with a 350.

I drove around a little today, and rodded on it a little. At full throttle it won't upshift unless you let off a little. And It won't shift to 4th until about 50 no matter the throttle position. And I don't think the TC is locking up.

So there's my longwinded story, any thoughts? Any advice on the tranny? Thanks.

[Edahall]

This is the first 6.2 I've ever driven so I don't know how it compares power wise, but it seems pretty peppy. I was once told that acceleration would be about like a throttle body 350, but I think we're better than that. Its deceiving with no exhaust, but it seems quicker than my last blazer with a 350.

I drove around a little today, and rodded on it a little. At full throttle it won't upshift unless you let off a little. And It won't shift to 4th until about 50 no matter the throttle position. And I don't think the TC is locking up.

So there's my longwinded story, any thoughts? Any advice on the tranny? Thanks.

Put that restrictive exhaust back on and you'll lose quite a few ponies. But yeah, with a non restrictive exhaust, the 6.2L puts out good power.

Make sure there is power going down to your transmission to ensure TC lock up. You might want to bypass the wiring circuit that's there and make your own circuit with a switch.

[Yukon6.2]

Hi Woodwright
My 6.2 was a bear to start when i use the 60 glows.Get a set of Quick heat glows from Kennady. Makes a world of differance.If you don't mind having a built for you truck you can put in a manual switch and keep the 60's on longer.
Thomas

[woodwright]

I would rather not have a switch for the TC lockup since 90% of my driving is empty, and the only thing I tow is my tool trailer that only weighs 2K. In my situation would there be a benefit to a manual switch?

Yukon, I already have a manual glow switch. I think around here its almost a necessity when it gets below freezing for 60 days at a time. Its pretty funny to see brand new trucks in the store parking lot that won't start.

Edahall, is duel 2 1/2" restrictive? If its the flowmasters, I was thinking of swapping them for straight glasspacks. Would that be better?

Thanks.

[Edahall]

I would rather not have a switch for the TC lockup since 90% of my driving is empty, and the only thing I tow is my tool trailer that only weighs 2K. In my situation would there be a benefit to a manual switch?

Yukon, I already have a manual glow switch. I think around here its almost a necessity when it gets below freezing for 60 days at a time. Its pretty funny to see brand new trucks in the store parking lot that won't start.

Edahall, is duel 2 1/2" restrictive? If its the flowmasters, I was thinking of swapping them for straight glasspacks. Would that be better?

Thanks.

Wiring in a switched 12 volt circuit would bypass the existing circuit. The existing circuit that goes through the brake pedal switch and throttle position sensor could be defective somewhere along the line causing your issue.

The stock exhaust setup is dual 2-1/4" and is pretty restrictive but does a good job at keeping the exhaust quiet. Straight glasspacks would help out some. Fabricating an H-pipe across would help some more. But none of this would help the restrictive bends. On my 1982 Suburban, I went with mandrel bent dual 2-1/2", H-pipe and headers. I could not be more satisfied. Much better power and better fuel economy.

[woodwright]

The PO put 2 1/2" duels on it. Whats the purpose of an H pipe? Does it make that big of a diference?

[Edahall]

The PO put 2 1/2" duels on it. Whats the purpose of an H pipe? Does it make that big of a diference?

The H pipe balances out the duals and makes it flow better. It also cuts down the noise. As far as difference, it's probably one of the better bang for the buck as far as increasing power.