I have an 89 chevy 1/2 ton 4x4 pickup with the 4.3L engine. Lately, I noticed when the engine is cold (starting for the first time of the day) that it idles like crap and backfires until it warms up. I popped the hood and noticed a small coolant leak between the intake manifold and cylinder head on the passenger side. I was just wondering if this is common with the 4.3L and if it is responsible for the engine idling so poorly when its cold. there is 80k on the engine, I checked the oil and it is free of coolant and the coolant level has not gone down in my truck.
------------------------------------------------------------------------------------------------------------------------------------- hey Matt you could be getting coolant in your cylinder that could be fowling out your spark plugs that could make it run like that are it could be that you need to look at your choke it may need to be replaced and the coolant is another problem like replacing the head gaskets. Mutt
Matt' have seen more than a few intake leaks like this, usually on the left bank though. be that as it may, let leak long enough will mess up the intake manifold requireing it to be replaced, And yes if its leaking coolant, it probably has a vacumm leak too. Once engine gets hot, manifold expands enough to seal again.
God save us from amateurs. 89 has throttle body, no choke cause there aint no carb. Leak is between intake and cylinder head, not cylinder head and block, which if you had read the post you would have known, there fore the head gaskets are fine.
this is what I thought was happening. Im assuming the backfiring is due to a rich air fuel ratio from the vaccum leak. The leak seems to be pretty small right now, any idea on how bad it can get?
It can get to the point it wont run any more. It can get to the point coolant wise where it starts leaking into the oil galley. Coolant and used motor oil form acids which eat bearings alive. It can get to where it blows a chunk of the gasket out and cooling system empties in 2 minutes, resulting is a long walk. The intake is aluminum. The leaking coolant can "erode" groves in the intake manifold and make is scrape metal. The manifold gasket is easy to change, about three hours with hand tools. I leave everything on it, drain radiator, just disconnect fuel lines and vacuum hoses, heater hose and upper radiator hose, throttle linkage, pull distributor, disconnect all electrical connections. I set it upside down on a right side up milk carton, and then scrape the gasket surface clean. Put lots of rags in the lifter galley of the block and then scrap the gasket surface clean. I stuff paper towels in the intake ports of the heads to keep debris out. 1-2" wide wood chisels make great gasket scrapers on cast iron, use a sharpened putty knife on the intake, as the aluminum is softer, and you don't want to gouge it. I like Felpro gaskets.
and its not going rich, its going lean, your sucking more air in.
dont assume the problem is the only problem on an older vehicle if the truck is running lean then it could be the vaccum leak but if it is running rich then it is probaly an isolated problem that does need to be looked at. if ti is running rich then the problem is most likely a map sensor or oxygen sensor check to see if there is a check engine light or service engine light if not they could still be the problems. the older vehicles were not as sensitive as todays self diagnosing vehicles especially if the problem is temporary as in it goes away after the vehicle warms up if there is a check engine light on then you can go to an autozone they will read the code for free instead of paying fifty or more dollars for a shop to do the same thing
I think i can change this myself, seems pretty straightforward. Pulling the distributor looks tricky however, as you have to have the No. 1 cylinder at TDC in order to pull it out. Can this be done easily?
No doubt about it. For that mater you don't need a code reader for an 89, you can do it with a jumper wire on the aldl connector between "A" and "B" which should be the two upper pins on the right side of the connector under the dash to the right of the steering column.. As to the lean/rich, I was stating that a vacuum leak will cause a lean condition, not a rich condition. The original poster stated he believed vacuum leak causing a rich condition causing the back fire. By age and mileage he's due for an O2 sensor. But I believe the biggest issue is the coolant leak. Its only going to get worse, and get more expensive to repair the longer he waits. I should have added he should have some vacuum hose on hand as he will probably find some hard as a rock when he goes to disconnect them. There are always a couple rolls of various size in the garage, and things always on hand sometimes slip the mind.
But then that's what's great about things like this, someone else stepping up to the plate to add to the info.
You can pull the dist out without being at TDC, you just have to mark it so you put it back the same as it came out. Mark the rotor to the housing, and the housing to the engine. Pay attention to the rotor when you pull it, it will turn a bit (cause of the way the gear is made) and it will have to turn the opposite way to go back. When you go back with it it might not go all the way but close. Just have a helper bump the engine over while you push down on the dist and it will drop in.
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