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  #1  
Old 04-02-2010, 11:20 PM
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Angry Rough Running, Rough Idle, Idles Hot

I'm pretty much down to my last nerve and this truck is parked on it. The latest problem occurred about 5 hours ago. While my son was about 3 miles from the house, it started running rough and shaking. Because it was very low on gas, he made his way to the gas station thinking that was the problem and brought the tank to half full. When he went to start it, it started a little harder than normal but it continued to run poorly.

When he got home, he told me what happened and he also mentioned that the transmission didn't sound right. I went out to take a look and the first thing I noticed was the smell of gas as I approached the truck. I turned the key and it strated right up but boy, did it idle rough and it shook.


Now, some more information:
  • 1996 4.3 Blazer, 150,000 miles
  • Engine light did not come on
  • Has a known coolant leak at the intake manifold
    • It's checked 2-3 times a week with the last check being yesterday
    • During this episode it was leaking but there was coolant in the reservoir.
  • It seemed to make an odd knock every minute or so while idling in drive. I couldn't tell if it was the transmission or if it was backfiring(not a gun shot backfire).
  • I checked the transmission fluid with it running and it park and it seemed low. Subsequent checks of the fluid level were normal. The fluid smelled different but I don't think I've ever smelled bad transmission fluid.
  • While sitting in the truck with it idling, I watched the temperature gage steadily rise past 210 up to 230+. At this point, the "Check Gages" light came on. When I steadily pressed the accelerator, the temperature rapidly dropped and I do mean rapidly.
Repairs within the last 3-4 weeks:
  • New serpentine belt and tensioner pulley
  • Heater core flushed
  • New O2 sensor
  • New distributor cap
  • New coil
  • New fuel filter
  • New fuel pump
So, does anyone have any ideas of what I might be up against?

Thanks for reading my post and your help is appreciated.

Ken
  #2  
Old 04-03-2010, 06:33 AM
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Quote:
Originally Posted by nhguy261 View Post
When he went to start it, it started a little harder than normal but it continued to run poorly.



Now, some more information:
  • 1996 4.3 Blazer, 150,000 miles
  • Engine light did not come on
  • Has a known coolant leak at the intake manifold
    • It's checked 2-3 times a week with the last check being yesterday
    • During this episode it was leaking but there was coolant in the reservoir.
  • It seemed to make an odd knock every minute or so while idling in drive. I couldn't tell if it was the transmission or if it was backfiring(not a gun shot backfire).
well Ken, it sounds like you already have the info right there-your lower intake gasket is more than likely filling up a cylinder (or two), fouling up the plug and causing your rough running condition.

and the "it started a little harder than normal" confirms (in my mind) that the truck is filling up the cylindar with coolant while it's sitting, thus causing the "hard to crank over" starting condition.

it either the LIG or a head gasket (which is what my '92 had when it started running like you described). how long has the coolant leak been going on? have you noticed any white vapour/smoke coming from the exhaust?
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  #3  
Old 04-03-2010, 09:28 AM
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Default Rough Running, Rough Idle, Idles Hot

old skool luvr

My son inherited the truck from my father in November and I know that my father had the coolant leak for years. His mechanic put something into the cooling system to slow the leak and it seemed to work for a long time.

We haven't noticed any white smoke coming from the exhaust but there's usually a little puddle of water under the truck if it's parked and idling. We've always considered that to be normal.

My mechanic mentioned the leak when the fuel filter was installed about three weeks ago and said that it would cost about $600-$800 to repair which just isn't in the budget. I don't like adding anything to the cooling system other than water and coolant but do you think it's worth the effort to flush the system, add new coolant and a sealer?

Ken
  #4  
Old 04-03-2010, 10:13 AM
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i'm not too keen on adding any of that leak stop stuff-not even the Bar's Leak brand, you never know what it could get into.

could you imagine the damage if your cooling system was breached into a cylinder? all that grit in between the piston & cylinder wall? then getting washed down into the pan & sucked back up through the oil galley's?

not a pretty sight.

do a little searching on here, you'll find it really isn't that difficult to do the gaskets yourself (it'll save you quite a bit of $$$).
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  #5  
Old 04-03-2010, 09:37 PM
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Default Rough Running, Rough Idle, Idles Hot

Good point on the stop leak stuff.

I searched the forums and found some great information...I'm pretty sure I can do this. My approach is typically slow and steady. With that said, I suspect this will take me at least 2 days and without a garage, the New Hampshire weather will stretch that even longer. I do have access to a garage that's about 15 miles away, is it OK to drive this vehicle that far, if at all? I read on one post that damage to the bearings can occur if the coolant has leaked internally.

Ken
  #6  
Old 04-03-2010, 09:58 PM
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you should be able to make it. i would change the oil before i drove it though, just dirt cheap 5w-30 is all you need.
  #7  
Old 04-16-2010, 06:52 PM
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The saga continues.

This past weekend, I replaced the intake manifold gaskets hoping that would fix 1) the coolant leak and 2) the rough idle. Well, I think it fixed the coolant leak but I'm not 100% certain because I'm afraid that if I take it for a good test drive it'll break down due to the rough idle condition that still exists.

I did some more research hoping to find and do some of the easy fixes before I have to bring it to my mechanic for the things that are over my head. Today I did the following things:
  • New PCV valve
  • Replaced the tube connecting the PCV valve to the manifold because the rubber boot at the manifold was wrapped with electrical tape.
  • New EGR gasket. The gasket looked questionable when I took the EGR off this past weekend but the EGR had no carbon buildup nor did the ports.
  • Cleaned MAF with CRC MAF cleaner. The screen nor the wires looked dirty at all.
I'm starting to fear a head gasket problem because today while it was running, I got the impression steam was coming from the exhaust but it was raining and the temperature was in the low 40's so I could be mistaken. Tomorrow I plan to inspect the spark plugs and test the compression. What is a normal compression reading?

I'll also be looking for vacuum leaks. Do you have any other suggestions of what I could check? I'll have access to a multimeter so can any key electronic components be tested? If so, would you explain the procedure?

Thanks
Ken

I forgot to mention.
  1. The engine light is not on. Would it come on for a bad head gasket?
  2. When it's first started, it idles very rough and seems to improve after 2-3 minutes. It gets a little better when it's put into drive but when the accelerator is pressed, it shakes and sounds terrible.
Thanks again
Ken

Last edited by swartlkk; 04-16-2010 at 07:13 PM. Reason: **Combining Consective Posts** - Please use the EDIT feature to add information to your post if another member has yet to reply.
  #8  
Old 04-16-2010, 07:42 PM
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Normal compression is kind of an odd thing.. Every engine is different. All of the cylinders should be within +/-10% of the average compression.
  #9  
Old 04-29-2010, 10:22 PM
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Default Problem Solved - Rough Running, Rough Idle, Idles Hot

The rough idle problem on my son's 1996 Blazer has been solved. Since my last posting, the following was done but none of them solved the problem:

IAC cleaned
MAP sensor tested normal
Compression test cylinders all were ~170 psi
Pressure tested the cooling system - no leaks
Fuel pressure tested at ~55 psi
Spark plugs replaced

After this, I drove it to my mechanic who found two things:
  • The new distributor cap was defective
  • Two spark plug wires had splits/cracks in their insulation
Problem solved
  #10  
Old 04-29-2010, 11:58 PM
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thanks for the update.

glad to hear it's all better now. too bad it was the long way around in finding the problem. but @ least you know the truck will be good for another decade or two. hopefully.
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'78 Chevy Silverado LWB, slammed (sold)
'79 Buick LeSabre 4dr, w/Olds 350 Rocket (1st ride)
'84 T10 Blazer w/8" of lift (sold)
'90 GMC Suburban SLE, a Canadian rust bucket (R.I.P.)
'90 Chevy Suburban Silverado, 6.2 diesel, a Southern Belle
'92 T15 Jimmy SLT, 4dr, 1 of only 2 factory 5spds. in Canada, and stupid fast (R.I.P.)
'95 Buick Regal LS, 290K, still going strong
'98 T10 Blazer LT, 4dr The Incredible Hulk
Old 04-29-2010, 11:58 PM
 
 
 
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