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Head on - Still have BIG Problems!


Everyone says I'm a jerk.
NAXJA Member
Torrance, CA
Oh damn...

Background: So I got stuck in Bakersfield, overheating, was still running fine, just hot. I parked it and came back three or four hours later and had no power. I knew I had a slightly blown head gasket (HC in coolant) so that was the idea...

Today: I finally got the freshly rebuilt head on (mine was cracked, had to find another one), put it on, got everything buttoned up, took it out...NO POWER!

Same damn thing. It feels a lot like fuel starvation (about the same symptoms as when I had really bad leaky fuel injectors). Hesitation and no power on acceleration, lots of backfiring out of the intake (fore-firing?). The idle varies from smooth as silk to rough as my jeans after all day wrenching. A little bit of hesitation when gunning the throttle with no load, but none of that popping BS.

I pulled my fuel filter (bypassed it), that didn’t fix it. I haven’t checked the output of my fuel pump, but it doesn’t sound bad. The plugs are new, as is the cap and rotor. The plug wires are not new, but this problem happened VERY suddenly, in any case I’ll be getting new wires anyway. The intake and exhaust are both good, no cracks, and of course fresh gaskets all around.

So...any ideas? The only thing I can come up with is Distributor, but I don’t see how that can go from perfectly fine to perfectly screwed just because I parked it...

Oh, one more thing...I’m still running hot as well. Got almost to overheat on a simple test run this evening, ambient temperature was probably 65 – 70, no hills or anything, no AC. I just flushed everything out in my cooling system...

I've thought a bit about that as well, because of the popping business. I'm going to reset the distributor just for kicks. I didn't pull it though (I never pull those things out unless I HAVE to!).

George -- any chance that you left the MAP sensor hose disconnected??

The fuel-pressure may be worth a look see (depending on how long it sat)

have you run a compression test?
I'm going to check the fuel pressure today probably (as soon as my emergency at work is dealt with). As for the MAP sensor..that's in idea, I'm sure the hose is attached, but I'll try to find some diags on it to see if maybe it failed on me....

As for compression...well, I'm planning on doing that and dreading it (damn numbers one and six cylinders are going to be a pain to do!)


PS - It's not George :) (Actually, the G. stands for Geoff, I tend to go by Sequoia because there's too many people around with Geoff sounding names, most of them spell it wrong though :))
I hate to be the evil one here but how hot did it get? If you cracked the head it's not too far off to crack the block.
Recently I didn't get it terribly hot. About a year ago I buried it in the red, I believe that's when my head cracked...

I think I'm going to take it down to my friendly dealer and have them do diags on all the sensors...
MAP check is easy -- (easier than figurin' where I came-up w/ George - sry 'bout that!)

Pin "C" should have 5Vdc while the key's in run.
Pin "A" is ground

Output from pin "B" should be near the voltage on pin "C" key on engine off
At idle pin "b" 's voltage should be less than 1.5Vdc (0.5 is fine!)
one more thing, when we repaced my engine, i sprayed the engine off with a pressure washer, got the engine in the next day, would crank and drive, just no power at all, wouldnt go but like 10 mph, turned out being the cps, i guess i wet it enoughh to mess it up but not totall kill it
All right kids, here's what I've done. First, I doulbe checked the firing order, all's good there. I didn't do the compression check, lazy.

Anyway, my MAP sensor is out of range. When the engine is idling and warm I'm getting 2.33 - 2.44 VDC, so looks like that may be the culprit, could a volt do that much you think?


PS- Anybody know where I can get a MAP sensor aside from the dealer? This is for an '89, so think Renix
After replacing my head, I got all kinds of hesitation and stalling. It would happen mostly at stoplights. I would have to keep my foot on the gas to keep the engine running. I tested all the sensors and all were within spec. Turns out, it was a problem with the EGR valve. After unhooking it, the engine runs better than ever and it passed emissions with flying colors...
For a MAP Try a Wells SU105 -- Autozone should have "normal store stock" for under $30USD

Did you verify that the MAP ground was good? -- If the ground is good then that volt off of the MAP will make a significant difference (really - you're looking at a sensor that only has a 3.5 volt range for output... so 1 volt is nearly a 30% oops...)

Before you go suspecting the MAP -- it's intended to sense manifold vacuum -- have you checked the manifold vacuum at several places? A leaky TB gasket can drop the Manifold vacuum and that'd show in the MAP as would other leaks -- could be that your MAP is reading what's there

(Nobody mentioned how fun leaving off the Head Ground Strap is -- I'm assuming that you've checked that and all the other sensor grounds??)
I'm lame - posting a reply to myself (I wonder if I'm listening??) --

Something that does point to the MAP and its vacuum harness are the backfires outta the intake (that little diaphragm doesn't hang well with positive pressures!) It's a fairly standard GM unit and should be widely available

so ??