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Author Topic: Detonation issue on Suburban  (Read 4029 times)

Offline crazedhick3

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Detonation issue on Suburban
« on: February 19, 2008, 07:35:53 pm »
1989 Suburban 350 TBI.  I have had this problem for a year or so now, but I dont drive this thing enough to really worry about.  I have set timing according to underhood decal.  0*@BTDC.  I only get the spark knock under load.  It will trip the Knock sensor code and clear up slightly but not completely go away.  Any suggestions?  Bad distributor?  Thought about maybe changing to an aftermarket HEI and change to Carb, but I really prefer the TBI.  Easy starts and cruise control.  Dont really want to give them up.  Any suggeations would be greatly appreciated.
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Offline VileZambonie

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Re: Detonation issue on Suburban
« Reply #1 on: February 19, 2008, 07:38:21 pm »
Did you open the EST connector when you set the timing?
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Offline crazedhick3

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Re: Detonation issue on Suburban
« Reply #2 on: February 19, 2008, 08:05:32 pm »
Yes
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Offline VileZambonie

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Re: Detonation issue on Suburban
« Reply #3 on: February 19, 2008, 08:09:49 pm »
Well many things can cause pinging. I will get into what to check in a minute, but 1st a few q?s

Does it do it when the engine is cold too? Is your EGR hooked up?

A few things to quickly check

Make sure you have the correct spark plug heat range. What # plugs are you running? Do you have access to a scan tool? Make sure you have no vacuum leaks. Does the check engine light come on?

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Offline crazedhick3

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Re: Detonation issue on Suburban
« Reply #4 on: February 19, 2008, 08:24:39 pm »
I will have to get back to you on the spark plug heat range.  What should it be?  I dont believe it does knock when cold but I honestly do not drive it when its cold.  I always start the truck to let it warm up before driving.  I guess I do that because I dont drive it  but once a week even if that.  eGR is hooked up and I went through alot of the vaccum hoses last year and replaced a few of collapsed and cracked hoses.  But I cant be sure I dont have a leak somewhere.  Other than the knock, I have realized the motor would stumble slightly at a stoplight.  Nothing drastic but a small stumble at idle after cruising.
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Offline VileZambonie

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Re: Detonation issue on Suburban
« Reply #5 on: February 19, 2008, 08:32:26 pm »
spray a little carb clean around the base of the throttle body to check for leaks there. Make sure you have good fuel pressure, replace the fuel filter if necessary and tune it up. Make sure the T-stat is working correctly. If everything is good and it's still pinging do a top engine cleaning. GM sells top engine cleaner or you can try sea foam. I've used both and prefer the results of the top engine cleaner. Make sure after you do it you change your oil & filter.
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Offline crazedhick3

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Re: Detonation issue on Suburban
« Reply #6 on: February 20, 2008, 08:52:18 pm »
Vile, thanks for all the suggestions.  Ill try it all maybe this weekend.  But one more question for all,  is the TBI worth keeping?  Or go with Carb, Intake and Cam kit?  Just debating.I really need to keep all my attention focused on my '77......
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Offline Redneckchevy

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Re: Detonation issue on Suburban
« Reply #7 on: February 20, 2008, 08:57:41 pm »
I would keep the TBI...Most every one wants to switch from carb to TBI...Your already a step a head..
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Offline Captkaos

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Re: Detonation issue on Suburban
« Reply #8 on: February 20, 2008, 09:17:25 pm »
The TBI is definitely worth keeping.  Better drivability, fuel mileage, longer engine life, auto adjusts for weather variations, etc, etc.
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Offline VileZambonie

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Re: Detonation issue on Suburban
« Reply #9 on: February 20, 2008, 09:19:10 pm »
Keep the TBI, you can still change cams and do anything you would with a carb with the TBI systerm
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