HT4100 4.1, 4.5, 4.9 Discussion, Newbie needs help with 87 seville 4.1L in Cadillac Engine Technical Discussion; I have just bought a 87 Seville 4.1L. with a misfire problem.
the guy I got it off said that ...
I have just bought a 87 Seville 4.1L. with a misfire problem.
the guy I got it off said that all the cylinders have good compression and he thinks that the misfire, that is on the second cylinder in from the drivers side on the back, is being caused by a split in the intake manifold gasket. he also said that when the engine is revved, it sounds like it is trying to kick in. could anyone give me some advice on fixing this. I hope to do it myself as I have some limited experience with engines but have never done anything like this, oh and living in the UK garages will probably charge extra. is there any easy way to check that it is not the injector? or should i replace it regardless when i do the gasket?
Also this is my first Cadillac, can anyone give me some general tips or advice that may be useful?
First lets make sure the engine has good compression. Can you do a compression test? Once you get the plugs out check them for color . they should be light tan to off-white on the center electrode with all the plugs looking the same color. If you find one that is much different , that is the cylinder to look closer at. I don't want to scare you but the early HT 4100 engines had some problems with the valve rocker arm mounts wearing out or breaking. You would hear it ticking and the misfire would not go away. Hopefully this is not what's wrong with your engine. Anyway, a good first step is to look at the plugs and test compression.
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Re: Newbie needs help with 87 seville 4.1L
While you have the plugs out, replace them with fresh. Check you plug wires for proper resistance. Check your cap and rotor and rule out your ignition system as a culprit. You should first get yourself an OEM service manual. they are available at www.helminc.com though I'm not sure if you will have any problems getting it in the UK.
You can also do a vacuum test on your intake, if there is a leak in the gasket it might show up in the vacuum test. I beleive you only have two fuel injectors just above the throttle body so those shouldn't be an issue with the miss to one cylinder.
While you are doing all this you will want to clean your throttle body. Do a search on throttle body here and follow Bboynski's instructions on it.
If you have to replace the intake gasket you should be able to with a good set of sockets, wrenches, the manual, patience and gumption. Take your time and take progress pictures for later reference replacing everything.
As said by Aaron, you need to first establish what the compression is. If I am right, they should all be in the 130-135 region +- 5psi. And look at the plugs for any variance off the nice tan colour to help locate the offending cylinder.
If the compression is OK, reinstall (or take the oppourtunity to replace) the plugs. Start the engine. By the sound of your description, the problem may be spark related.
Take a self powered test light and ground the end to the engine and probe each of the wires. Take care to do this as not to ruin any wires. You have to slide the test light between the boot and the wire on the cap end. This will short out the spark to an individual cylinder. As you do this to each cylinder, you will notice an increase in the roughness of the engine. When you get to the one where there is no change, you have found the offending cylinder.
Shut off the engine and remove the wire from the plug. Use a spark tester, or if you do not have access to one, inser a screwdriver into the end of the wire and restart the engine. Hold the screwdriver about 3/4" from a ground and you shouls ee a good healthy spark. If not, replace the wire and try again. If there is still no spark, remove the cap and inspect inside for carbon tracking and the condition of the tower. Replace the cap and you should be good to go. While you are in there, replace the rotor as they are known to carbon track in the centre and cause hesitations, stalling and no start conditions.