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LT1 fun


Richard Cranium

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Hey folks. I'm curios of peoples ideas.

 

A couple weeks ago the LT1 started running rough. Was running fine one minute, then started acting up. Very drivable, no codes, but not right. We started looking for a vacuum leak and found a possible small one. While waiting for a replacement MAP sensor seal I decided to keep poking my head around. I found an fixed another possible vacuum leak.

 

When I took the car for a test drive and couldn't tell a difference. When I got back to the house I was letting the motor idle in the driveway while I continued to look at listen. Then I noticed the temp gauge was way high. I shut the motor off and started investigating that. Turns out I was low on coolant, so I topped it back up and bleed the system. I do have all the air out of the system, but the temp keeps creeping up.

 

Today, I head back out to continue troubleshooting and find a spark plug wire rubbing a pulley. It has rubbed through to the core, so I'm relatively confident that explains the running rough. But the temp problem is still bugging me. I check and see and the cooling fans are not running on the radiator. I've never had a problem with them before, so I plug my laptop in and the PCM is seeing temps of 168 - 172 while the dash gauge is reading well over 200 and climbing.

 

I figured it was worth throwing a new sensor in and see if that solves things. But it does not. I continue seeing wildly different numbers coming from the gauge and the PCM. BTW, I know the thermostat is opening because the radiator is getting pressurized when the engine is warm.

 

Since the gauge is fed by a sensor in the drivers side head and the PCM gets it's signal from the sensor in the water pump I'm starting to wonder if the water pump is not circulating coolant. I don't think there is a way to measure coolant flow. Is it worth pulling the water pump and checking it out? It wouldn't break my heart to do that since swapping out the bad spark plug wire would be easier without the pump there.

 

Any thoughts, ideas .... am I on the right track?

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What is voltage reading on your laptop ? Possible alternator may be going bad ?

 

PCM is seeing 13+ volts

 

Headgasket? :eek:

 

Pressurized when warm, disappearing coolant...

 

I am afraid of that, but once I got the air burped out of the system it seems to be holding coolant. Every time I crack the bleeders now all I get is coolant coming out. Also I don't really smell anything sweet at the exhaust. Not sure that means anything though.

 

http://t1.gstatic.com/images?q=tbn:ANd9GcTBza113FBC7wNSyr9Y662HuWhk1siPuxXEVvygiBgxwp5_dvY&t=1&usg=__JOr9SJ1Y7TvPgwVE03hJfEwWRQE=

 

Yeah, that is probably the best idea at this point. I'm terrified of over heating the motor at this point and turning a relatively small problem into a major one.

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Call me if you need any help Rick I'm just over in galloway 6146339662 I can swing by sometime today

 

Thanks guy. I'm going to run and grab a gauge. I have family coming over for dinner later, so I probably won't get much more done this evening. I just want to make sure I get this squared away for the track day coming up.

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Okay, mechanical gauge reads the same as the dash gauge. I watched the PCM reading and the mechanical gauge side by side. Both started under 100 degrees. In the time it took the PCM to read 100 the mechanical was reading 160. I can verify the coolant is not 100 degrees as I cannot remove the mechanical gauge until things cool down.

 

Once things cool down I'll move the mechanical gauge from the head to the water pump and try this again and see how quickly it heats up.

 

The only reason I can think of that the coolant temp in the head would increase faster than the coolant temp in the water pump is that the pump is either not circulating at all, or only a little.

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Try jumping the hot wire on the fans. So that the fans run all time and see if your still having a cooling issue. Then I would look into swaping the water pump

 

Tested with the gauge in the water pump this time. I'm still seeing huge difference (I saw a 100 degree difference once) between the pump and the head. Also the temp in the head climbs 5 times as fast as the temp in the pump. I'm seeing this the whole time the engine is running, before and after the thermostat opens.

 

do a compression leakdown test

 

Yeah, I do need to do a compression and a leakdown test. I just hate the idea because of how much work it will be to test all 8 cylinders.

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if you have LT headers, the compression test isn't too bad.

 

I had this issue with my car before, turned out I still had air in my system... that reverse cooling that the LT1's have is a real bitch to get all the air out.

 

Yeah, I have long tubes, but it still sucks. Also I have a compression gauge somewhere, but I'd have to rig something up for a leakdown test. I could go back to trying to burp air out of the system. Maybe try a few more tricks, like putting the front end up on ramps to raise the thermostat and the bleeders. Maybe even remove the thermostat for the process.

 

I'm stumped though on why the HUGE difference in coolant temp between the head and the pump. Even with some air in the system I would not think there would be a 100 degree difference. It doesn't sound likely, but the only thing that really makes sense to me is the pump isn't circulating coolant. So the coolant in the head just sits there and heats up, and the coolant in the pump heats up but much slower.

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I'm not sure which was more work, putting the engine back in after the rebuild or trying to get this stinking water pump out with the engine in the car. This sucks.

 

Anyhow, I figured she needs a new water pump regardless since it's still the original pump and now 145k on the clock. I have the pump loose and when I turn the pump drive shaft it does turn, but grinds. I ran out of light and patience this evening. I'll go back after it tomorrow and get the old pump out to see if it was running. Either way the new pump will go back in. With the pump out it will be easier to replace the fubar'ed plug wire.

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I probably will eventually. Right now I'm trying to get it back up and running so I don't miss the track day. Initially I didn't install an electric pump because I liked the idea of the mechanical drive, if the engine is turning the pump is turning. There is no core charge on my new pump so I can take the old one and install an electric drive later if I like.
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Hmmmm, is it a problem if the water pump drive shaft spins, but the impeller does not? Something tells me that is a problem. I have to run to Jegs anyhow to pick up a new spark plug wire set, maybe I'll grab an electric water pump while I'm at it and take back the new one. Thanks for the idea Ant.

 

Anyone know how to wire one of these up? I heard somewhere you need a relay to run the pump because a regular switch will burn up. I would want it running whenever the car is running without having to remember to turn it on.

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In that case, wire it to ignition and ground and it will run only with the engine running.

 

Some people like to install a switch to leave it running in the staging lanes with the car off, then you'd need a relay to keep the switch from frying.

 

And yes, the shaft spinning with the impeller staying put is bad :)

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I grabbed a Meziere last night at Jegs. We'll have to get the guts of the old pump pressed out before I can get the rest of this done. Luckily we have a press in the autotech lab here at school so I should be able to get that done today. With a little luck and some work I should be good to go by the end of the weekend.
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