New motor. Ran fine. Now problems

[david-b]

What's up all?!

Finally been nice out so decided to start putting some miles on the built 420a. On Sunday was cruising around boosting trying to not hit over 10psi. I had the over-boost on MegaSquirt set to 12. I know I hit that once. MS was logging, but ended up corrupting the file so now I have nothing from the runs.

Long story short, I'm coming off the expressway, pop the car out of gear, and it dies. Start back up, dies again. Basically won't idle without me giving it gas. Babied it home, and still died. Checked under hood, no leaks, no nothing. All vacuum lines to MS are good (checked again the following evening). The car starts and idles now, but a low idle, and when I rev it, it's fine, but when the rpms come back down, it gets too low and sometimes dies there too.

Compression test came back as: 175 - 140 - 165 - 185
Pistons are 8.8:1. No overheating. Spark plugs are oil on top of them when I pulled out the wire, but I'm guessing the valve cover didn't seal too well.

I sadly did not take one before I started running her
So obviously, something is wrong here. Motor has about 270miles on it. Any ideas on what could have happened? MS is not fully dialed in, have her running richer than she should, just to be safe.

 

[Doctor DSM]

Funny thing, I just posted in another thread all the reasons (or some) to why the guy should NOT bother boosting his 420A, and there you come up like a X-mass gift to confirm that. Thank you.

 

[dsm'r sk1mp]

You know, on this site we like to only comment to help others when needed, or when beeing asked for help. im not trying to critizise you but this guy is asking for help and not for some one to come along and bash on the build he just did. OP- what i would do is check the idle control and your fuel lines. it might be the idle senser so try to adjust that. if you already did this then i appologize and ill look more into what it could be.

 

[david-b]

Funny thing, I just posted in another thread all the reasons (or some) to why the guy should NOT bother boosting his 420A, and there you come up like a X-mass gift to confirm that. Thank you.

Ya seriously guy, that's a douche remark. Mines is fully built, just like numerous of the 4g63s here. You guys have problems too, so please, keep it to yourself.


Moving on...
IAC is disabled. MegaSquirt is controlling the idle. I haven't plugged the IAC hole yet, and I know boost can blow open the IAC, but usually not til about 15psi. And that would cause high idle from extra air blowing in.

Fuel is all good. All stainless steel lines in the bay, no leaks or anything. Static pressure is perfect at 25psi, controlled via SFMU.

I guess I'll start pulling it apart this weekend and see what happened. The compression numbers are bad anyways so there's something going on in there.

Thanks dsm'r sk1mp

 

[95talongirl]

That one lower compression number concerns me. Did the timing belt slip?

 

[david-b]

That one lower compression number concerns me. Did the timing belt slip?

No it's still straight on there. All of them would have been lower.

I got it half torn down last night and just have to pull the timing belt to get the head off now. I'll be taking it to a machine shop to check for flatness. It was machined many years back when I originally built the head, however, it has overheated once or twice before, not too bad, but enough. Wouldn't hurt.

I'm going to pull the pistons and check all the rings and make sure they're all good and replace if needed. This was my first time gapping rings, so who knows how that turned out after they were installed.

Only thing I noticed so far in the tear down was the valve cover didn't seat properly at all. All seals were leaky, so doing all new gaskets for that and applying gasket sealer on all connections there.

Also pulled all the emissions junk finally as well. Sadly, it's going to be cold this weekend and snowy so not sure how far I'll get along since it's not in a garage right now.

 

[david-b]

Question, I've got the head off and so far everything is still looking good. Rings are on their way in. I was told I was going to have to hone the cylinders. Is this true? The block only has ~270 miles on it and the walls are undamaged. Cross hatching is still visable.

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[BogusSVO]

It would be best if you did hone the bores, so the new rings can seat in sooner/better

 

[dsm'r sk1mp]

it wouldnt matter if you did this 200 hundred or a thousand in to the miles of the block it is always the best to hone the cylenders so the rings can properly sit faster and right. on the idle problem for the beggining of this thread i would also like to mention that it might be possable that your CAS is of a little bit. its just something to look at is all. let us know how things are going

 

[vinnio]

did you do a leak down test before you pulled the head?

What head gasket did you use? Would be my first guess. Did you find out if it was warped or not?