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Post head gasket frustration

Posted: Mon Mar 29, 2021 3:20 am
by mr.blub.blubs142
I just finished up doing head gaskets on my 91 n/a legacy. Everything went fine and dandy until I tried firing it up. I cannot get it to run right and am currently stumped as to where to look. The car starts up and runs fine when it’s cold IF I don’t touch the throttle. It’ll run until it’s warm then shut off. I can only get it to start back up if I hold the throttle down and once I release it, it dies again. If I try to touch the throttle or shift out of park (even when it’s cold), it immediately dies. I triple checked my timing before I put the engine in and it was spot on so I don’t think timing is an issue. I haven’t checked compression yet, but I would assume it was good since it idles fine until it’s warm. When doing the job I replaced the knock sensor since mine wasn’t good looking and had a messed up connector and I replaced the coolant temp sensor since I broke mine. I also replaced a couple of the small coolant lines that go between the throttle body and the IAC. I couldn’t find molded ones so I just used standard, flexible hose. Anyone have any ideas for what to look for?

Re: Post head gasket frustration

Posted: Mon Mar 29, 2021 12:33 pm
by arse_sidewards
You almost certainly have an electronics issue. The computer is trying to give the engine fuel/spark for conditions that do not match what the reality inside the engine is. Sounds like something is failing when it goes into open loop based on what you said about warm/cold. To get problems this big you need to have a very important sensor be spewing bullshit readings or no readings. That basically narrows it to the air sensors because the engine wouldn't run without crank position and all the other sensors. O2, throttle, cam, etc. etc don't make enough of a different to make the car die, run rich/lean, yes, but not die when you step on it. Fuel, ignition and compression problems don't generally behave how you're describing with regard to warm and cold. Dying or running like crap when you reach open loop is classic MAF/MAP sensor failure symptom.

Check the connection to each sensor and try running with each one unplugged individually. If that doesn't make the source of the problem obvious then clean them both.

Re: Post head gasket frustration

Posted: Mon Mar 29, 2021 4:44 pm
by mr.blub.blubs142
I was leaning towards maf but wasn’t sure. I was actually going to replace it with my spare, but of course, I can’t find it. I’ll report back if a maf cleaning or replacement fixes it or not

Re: Post head gasket frustration

Posted: Mon Mar 29, 2021 5:42 pm
by Legacy777
I would lean towards the MAF sensor as well. I'd also suggest checking the ECU for codes if you haven't already done that.

Let us know what you find out.

Re: Post head gasket frustration

Posted: Mon Mar 29, 2021 8:08 pm
by mr.blub.blubs142
I tried it with the maf unplugged and couldn’t get it to run at all. I checked codes yesterday and I had 21, 23, 24. The 24 was because I forgot to plug back in the iac after I swapped to a different good one to see if that was the problem. My coolant temp sensor almost doesn’t feel like it’s plugging in all the way, but I could also just be imagining it.

Re: Post head gasket frustration

Posted: Mon Mar 29, 2021 9:00 pm
by mr.blub.blubs142
I just pulled my timing cover off to double check my timing just in case it was off and I didn’t notice. It looks spot on, though I did notice that the new belt has left a lot of greasy grime on the idlers

Re: Post head gasket frustration

Posted: Wed Mar 31, 2021 7:43 pm
by Legacy777
Typically you troubleshoot the lowest code number first. I would suggest clearing the codes, verify the codes have been cleared before starting the car again, try starting the car again, and then check the codes to see what has come back. That will help with narrowing down what could be phantom codes.

Some additional comments, the wiring in these cars are now old and brittle so it's possible that when you replaced sensors and did the work moving wiring out of the way could have caused a crack or break in the wire. I had this issue with the knock sensor and ended up just running a new wire from the ECU to the sensor since it's such a low voltage.

You could try checking the resistance of a few key sensors from the sensor plug to the ECU pin to ensure the wiring is still good.

Re: Post head gasket frustration

Posted: Wed Mar 31, 2021 7:58 pm
by mr.blub.blubs142
I found my spare maf (I believe it works properly though I’m not sure). I tried it with that and also cleared codes. It seemed maybe a little better, still dies and I now have no codes at all popping up. I pulled the spark plugs out and looked at them. They were completely carbon fouled so it obviously was running pig rich. I picked up new plugs and will try it later today with those. I did also realize that I had picked up different plugs from normal when I changed the gaskets, so perhaps having the different plugs could be causing part of the problem?

Re: Post head gasket frustration

Posted: Wed Mar 31, 2021 10:48 pm
by mr.blub.blubs142
I put the new plugs in. Still dies and no codes showing. I only tried it twice cause I didn’t want to foul up the brand new spark plugs...again. I tested the resistance on all the injectors and I got 13.6 ohms, 12.4 ohms, 13.7 ohms, and 15.8 ohms. All of the injectors are original except the one with the 12.4 ohm reading. Are those normal readings for them?

Re: Post head gasket frustration

Posted: Thu Apr 01, 2021 6:06 pm
by Legacy777
The specification for good injectors is 11-12 ohms. I don't think your injectors are the problem.

Is your car AT or MT and what color is your MAF sensor?

https://www.main.experiencetherave.com/ ... sting1.jpg
https://www.main.experiencetherave.com/ ... sting2.jpg

Can you run these checks on the MAF sensor making sure to check the body harness wiring as well.

Also, out of curiosity have you tried unplugging the coolant temp sensor and tried starting it?

Re: Post head gasket frustration

Posted: Thu Apr 01, 2021 6:48 pm
by mr.blub.blubs142
My car is an auto. It has a black plastic and green label maf. I have tried to start it with the coolant temp sensor unplugged. It turned on the fans and did not want to start.

Re: Post head gasket frustration

Posted: Thu Apr 01, 2021 6:55 pm
by Legacy777
Ok, can you run the checks on the MAF sensor and MAF sensor wiring and let us know how that checks out.

Re: Post head gasket frustration

Posted: Sat Apr 03, 2021 7:53 pm
by mr.blub.blubs142
I was able to check some of the stuff out on those tests. The ecu checked out fine and the wiring looked like it is good too. I’ll put a different maf in it this weekend and see if it runs then.

Re: Post head gasket frustration

Posted: Sat Apr 03, 2021 11:31 pm
by mike-tracy
Is it possible that a rubber hose or other object is pinched in between the intake manifold and the heads? I did that once and had similar symptoms (seemed like I had a vacuum leak, and turned out I did)

Re: Post head gasket frustration

Posted: Sun Apr 04, 2021 7:08 pm
by mr.blub.blubs142
I tested some of the wiring for the maf and it didn’t seem like there was a problem with any of it. I picked up a new maf from oreillys too and tried that. Still won’t run with the brand new maf. I’m about to the point where I might just pull my intake back off to make sure nothing got caught underneath it when I put it on

Re: Post head gasket frustration

Posted: Mon Apr 05, 2021 3:30 am
by mr.blub.blubs142
So for funnsies today I decided to try and get it to fire up with the o2 sensor unplugged. With the o2 sensor unplugged I can actually get it to idle for 15-20 seconds in gear before it dies, where as with it plugged in it immediately dies. I also don’t get any codes for it when it’s unplugged, which seems odd to me. I did forget to unplug it when I had the engine out so my exhaust was dangling by the o2 wires for a bit.

Re: Post head gasket frustration

Posted: Wed Apr 07, 2021 7:16 pm
by mr.blub.blubs142
I put a new o2 sensor in it. It still will not run when it warms up. Once it starts to warm up, it stalls out. It doesn’t sputter or try to stay running either. Just completely off like I turned the key. I’ve replaced almost every sensor now and I haven’t found any wiring issues or vacuum leaks. It’s weird cause it’ll hold an idle up until it starts to warm up. Once my gauge starts moving, it won’t stay running.

Re: Post head gasket frustration

Posted: Thu Apr 08, 2021 6:36 pm
by Legacy777
This really sounds like the ECU is getting bad sensor data and causing your issues.

My suggestion at this point would be to use a multi-meter and check the resistance of the wiring from every sensor back to the ECU.

Out of curiosity, have you verified that the ECU is getting good voltage and is grounded properly? The ECU grounds through the wiring harness on the back of the driver's side intake manifold.

Re: Post head gasket frustration

Posted: Sat Apr 10, 2021 2:24 am
by mr.blub.blubs142
I’ll try to take a look at the wiring this weekend and see. I’ll double check the grounds too. I ordered replacement vacuum/pcv lines which I hopefully will get in a few days. The curved hose that connects into the pcv valve disintegrated in my hands when I tried to remove it. A couple other lines were pretty dry and brittle as well.