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I have a sick 4cyl and I was bored so....


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I am planning on replacing the engine so I figured that it wouldn't matter if I cracked the cover and took a look at the valves on the off chance there was a simple and obvious fix that would get my truck back on the road temporarily (and give me a manly sense of mechanical prowess- which, you have to understand, I am a writer :typing: not a gearhead so it would be neat if I could feel competent working on the simple 4 cyl I have)


My 4 banger has been backfiring through the TBI so I am looking at the exhuast valve as a probable culprit. I think it has a rough spot where the valve sits (on the underside of the head) but I don't beleive there is any way that I can check this from the top of the engine with the cylinder head still mounted. Maybe I am wrong.


At this point I am doing this because I want to get more comfortable under the hood and since I am replacing the motor, and the truck isn't essential at the moment, I can't really screw up alot of stuff.


Looking at my Haynes it says I can idle the truck with the valve cover off- which I really can't believe (section 2-8), it says you can feel if there is a problem with the valve while it is running at idle with finger pressure on top of the armature. This sounds like a good way to blow oil all over my engine bay (and me) not to mention a good way for a unskilled but curious apprentice in the mechanical arts to really cause some mayhem... So I'm avoiding it.


I may pull the cylinder head just to see what the underside looks like, I am already part way there... :dunce:


BTW is the fan supposed to be able to freely turn? Is it clutch driven or something?


If anybody wants me to I will take some pics tomorrow.

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Go with the basics : Compression test , (check the plugs while their out ) , spark on all 4 ? , then follow your curiousity to the mysteries of the innards . And yes its OK to run the engine sans valve cover for short periods of time , rags around the perifery are a prudent precaution (you will get splattered a bit ). Have fun , count your digits after . :cheers:

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If youre getting backfires through the TBI, it can not be an exhaust valve. It would have to be an intake valve if that is the problem at all. The exhaust valve has no direct run to get to the throttle body. If it is an intake valve, there could be a buildup of carbon on the backside of the valve causing the valve not to seat properly which could cause a backfire into the intake manifold. That problem if let go long enough can also burn a groove in the valve... for which the only fix is to remove the cylinder head and replace the valves, and seats. You can test for this by doing a cylinder leakdown test, which takes an air compressor and special tools, so if you want to do this you may need to take it somewhere. Let us know what you find or if youre just going to give up and swap! We won't hold it against you either way.

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LOL, I'm not going to rev it up.


My mechanic did the compression test on cylinder 1 and we could hear air escaping (through the exhaust we thought). All other cylinders had normal compresion given the age of the original engine (223k). My mech said to replace it - it would be cheaper for me.

The part that was so puzzling, at least to me, is why it would run fine for about five minutes, I could rev it all the way up and shift and rev again, and then it would start backfiring into the TBI when I hit the gas, and it hit on that cylinder. (Just recently I fould an abrasion/burn hole in the PCV line where nothing contacts it. So the air fuel was too rich?)

So I have the valve cover off and I'm debating just putting it back together for now, going the replacement route (going for a new engine), or it is going to be worth my time to explore further?

Things I know (be nice lol)

1 Timing chain not ever replaced

2 truck was not running, had original wires and coil when I got it and I replaced them- it ran beautifully for 5 months and got 33 mpg (thats why I love the little guy and would spend money and time on it)

3 The PO changed out the lower part of the distributor, I replaced the cap.

4 the plugs are not fouled

5 engine never rebuilt

6 new engine with warranty is going to be a 1000.00 ish

7 I hate the idea of scrapping a car and going out and spending 12k on a newer one without any guarantees... I will replace the engine or fix it.

Yeah I'm stubborn :thumbsup: but I don't want to be a complete :dunce:


What do you think? :huh???:

Timing issue. Engine Fubar'd. Just replace it and quit taking up the forums time.... (frankly probably the most certain course.)


Thanks for your input, I will post pics on Wed, that my soonest day off.

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#1 compression loss could also be head gasket ,since your in there anyway ...pull the head ,take a look , do the valves (cheap) check for cracks etc. ,put it all together again . The bottom ends on the 2.5 are very stout , chances are , re-freshing the head and a new timing chain will give you many years of good service .(NOMB but find a new mechanic ) :cheers:

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