Dies on start without gas 1980 280zx NA

[BluDestiny]

Ok so what my car does is as soon as I start it, it will turn over nice and normal, but then die out unless I give it gas and let the tach "smooth out" as it were instead of bouncing around. once it is equalized its fine though. Just on start up, after its been sitting for 30+ min.

 

Backstory:

 

My car was fine driving around last week. Took it on a 1 hour drive to Orlando with my GF and back. Had no problems, on either trip. I was a little low on gas, below 1/8 of a tank by the time I got back home, I don't normally let it run that low.

 

Next day I drive it to work and again no real problems. Then when I try and leave it won't start. I had to really give it gas to get it to start and stay on. A little embarrising, but that's what old cars are for. I hadn't filled up yet mind you, but a round trip to my work is like 4 miles. I get it home and park it, planning on checking it out in the morning.

 

Morning; I try and start it and it hardly runs, like its running on 3 cylinders. My assumption was that it just needed gas, as this car hasn't given me problems yet since I got it running in November of 2011. I daily drive it so I would notice little things, but I've never had an engine problem.

 

So I get some gas and it seems to start a little better, but then 2 hours later after it cools down, no dice. I can't even get it to start. I assumed that the O2 sensor is gunked up since the car runs a little rich, so I go and get a replacement that day put it in and it still doesn't run that well.

 

Next day; So I checked the dizzy and the cap and rotor were corroded. I'm thinking that's the problem, I picked them up today and put them on. It starts but takes a while for it to settle out ( the rpms I mean), drive it around the neighborhood and bit and it dies as soon as I always shift to neutral like when I come to a stop sign. Other than that it was running good when it was in motion and in gear, had a little trouble revving past 3k, but that went away after 10 min of driving. So I get it back to my house let it idle for a bit and begin checking if all the injectors are firing, they are. So I notice the volt meter is a little low, so I tighten up the belt. I also mess with the TPS ( turned the whole unit clockwise) and the idle screw ( turned it out ever so slightly). Take it around the block and it runs like a champ. It smoothly comes down to a nice idle at 750-850, and doesn't hiccup a bit.

 

So I bring it back in, shut it off and start it back on again without having to give it gas. about an hour later I went back out to check on it and it wouldn't start without a light feathering of the gas until the rpms equalized. Had to shut it off and head to work before I could mess with it more. I'm actually thinking that the problem will only be worse when the car is completely cold.

 

Side note: The fuel pressure is set to 35 according to my aeromotive FPR. There is a slight leak that depressurizes the rail when I shut it off after about 20 min, but it has never been a problem. The car would start normally when it read 0 psi.

 

So if that was a little long, things I did do: Replace o2 sensor, replace dizzy cap and rotor, adjust the tps all the way clockwise and turn out the idle screw a tad.

 

Car runs fine when it is moving and driving. Just the start up is annoying.

 

Car is a 1980 280zx base model, I have a shaved intake with no idle up or cold start injector, and 6-2 headers. I had the o2 sensor installed right at the collector instead of just on one of the runners.

 

I will upload pictures of anything anyone has a question about, maybe even a video of what is going on if need be.

 

Lastly sorry for the amount of detail, but I've learned that detail will only make it easier for everyone.

[Heroez]

Sorry to hear about your car trouble, it reminds me of mine. Do you get a five second fuel prime before you crank the car? What is the temperature of the car just as you park it? Once the water pump stops and you park, and no air flow, the temp climbs before it eventually cools down. Does your aux fan come on after 3 minutes of being turned off after driving? These questions plus your fuel pressure dropping could be heat soak. Heating vapor in the rail causes more problems than heating a pressurized rail with fuel in it. No fuel prime would not cycle heated fuel or vapor out. Aux fan coming on would indicate a cooling problem that compounds existing problems such as described. Unfortunately I have yet to discover why one day my fuel prime stopped working on my 1980. Try to fill in the answers to these questions to verify or rule out heat soak.

[BluDestiny]

Vapor lock has never been a problem to me before, but the temp gauge is just a tab before half. That's normal for it.

 

I do not have a fuel prime...I didn't know the ZX's had that. My 81 didn't have that either

 

Also I don't have an aux fan. I only have 2 12" electric fans to my radiator with a shroud. I'm also running a pallnet like fuel rail and an N42 shaved intake.

 

This is roughly what it looks like minus the harness

 

Really don't think its heat soak, only because I've been driving it all summer and its been much hotter ( the car and ambient temp) and I still haven't had problems.

Edited July 29, 2012 by BluDestiny

[78zstyle]

Honestly sounds a lot like heat soak.

[BluDestiny]

Not heat soak. Like I said it has defiantly been hotter and I have not had this problem. I've done autox events shutting the engine off after a lap and starting it back on again 15 min later for my next lap and it never had this problem.

 

Messed with it again, changed the tps position back to about where it used to be and changed put the idle a little lower. Was working better, but on decel it would pop and backfire out the muffler bad. Worse than normal. At least it started and idled fairly normal.

 

Also while I was going through the gears every now and then when I would floor it it would just hit a wall, like a rev limiter, at 3k. Mostly in 1st, 2nd and 3rd since I couldn't get up to speed. This would happen every other time I took off from a light almost at random.

 

The starting issue isn't there any more either. It seems to just start up just fine now. At least tonight it did. I will report more tomorrow.

 

I'm almost convinced it's something like the timing is just slightly off. Like the rattling of the car just moved the dizzy a little.

[neotech84]

Have you checked your AFM? And double check your grounds.

[BluDestiny]

OK messed with it a little more today and took a video

 

 

Ignore the first start, but at 10 sec you can see how low it idles. I try and rev it and it sounded off so I let off. At 40 I shut it down, at this point the car has almost reached operating temp and I restart it without any throttle help. It just starts then flops. Last start I use throttle and then let off and it very nicely comes down and lopes from 500-750rpm.

Edited July 29, 2012 by BluDestiny

[BluDestiny]

Ok update, decided to check the spark plugs and they were black as coal.

 

 

So I got some new ones popped them in and nothing changed. At this point I gave up and brought it to my mechanic. He said its probably the afm or cylinder head temp sensor on the side of the block. He took out the fsm and told me to find out how to test them.

 

Found that with a mulitmeter the cylinder head temp sensor should be reading between 2.1k ohm and 2.9k ohm. Well it was reading 1.4k ohm. Ok so I need to replace that. He also told me to check the afm since it was easy to get to and it was his multimeter. well turns out the air temp sensor in the afm is off too. fsm said between 2.1-2.8k ohm, and it read 1.4k ohm.

 

 

So I ordered a new cylinder head temp sensor and need a new afm asap.

[neotech84]

Yay me!!!

 

Glad you got it figured out.

[BluDestiny]

Yeah kinda short lived. I can't order a new afm from MSA since they need the part number and my afm had the sticker scratched off. So I'm basically gonna start converting to turbo. Sooner than I expected but meh. Should be fun.

[BluDestiny]

OK so I found someone selling the correct afm part number for pretty cheap. I had to get my friend to check the afm that I use don his car since it was originally mine.

 

Anyway I changed the chts and it ran a lot better. Still not perfect, like I wouldn't drive it somewhere. I'll post again on Monday when I have get my new afm in the mail.

 

Couple questions, when I changed the chts it was bone dry. Does that mean the head coolant drains into the block? Sounds like a noob question, but its the first time I replaced it.

[BluDestiny]

ok so I got the new afm in and it sounds smoother, but it still won't for the love of me idle. It just keeps dying. I used a 2x4 to chock the pedal at around a 1000 rpm idle.

 

I messed with the idle screw which helped some, but messing with the tps or the o2 sensor does nothing. If I remove the chts it dies, and likewise if I unplug the afm it does.

 

One other strange fact, the intake near the 4th ( counting front of engine to back) runner is cold. Like 30 degrees colder than rest of the intake. It actually started to form condensation.

 

Does anyone have any ideas?

[NewZed]

If it will run but won't idle, and the idle adjustment screw doesn't have any effect, I would look for vacuum leaks. That would lean out the mix, causing cold start problems that would diminish when warm. A hose might have split. Don't forget that the PVC system is connected to the intake.

[BluDestiny]

well after more coaxing, and probably burning off all the excess gas that was in the cylinders I did get it to run. The idle screw was just really turned in and that's probably why I didn't notice an effect.

 

It pretty much runs and drives but.....

 

I still have a few problems. I managed to get it to idle, like I said, but once I try and adjust the screw down to 750rpm it will start acting like its being choked. This AFM doesn't have an adjustment screw like my old one, so the idle screw on the throttle body is the only thing I can use.

 

Now if the idle is up at 1000-1100rpm it will run and start no problem, but when I floor it, I get a lot of hesitation from 3000rpm-3500rpm or until I shift into second. this only happens on 1st.

 

But when I adjust the idle down to 750 rpm it will not have any hesitation, but will not start on its own ( I need to give it gas).

 

I haven't ruled out a leak, so I'm going out now to test with some carb cleaner. and probably sand a few more connections down.

[BluDestiny]

well after messing with it more, I've set the idle at 900 and changed the tps a more to the middle. It seems to start up and idle, but I haven't let it fully cool down. There are no vacuum leaks thank gosh, I sprayed carb cleaner everywhere to try and find one.

 

Still getting hesitation at like 75% throttle, but full throttle is good and so it just slowing climbing up.

 

I still think it has something to do with the a/f ratio.

 

I will report more in a few hours once it's cool.

Edited August 6, 2012 by BluDestiny

[BluDestiny]

No go, when I went to start it up this after a slight cool down ( temp gauge had just moved past the 120* mark) it was just like when I first started it up. It wouldn't hold idle, and the intake got cold near the middle again. Does anyone know why this is happening?

 

here is a pic so you don't think I'm crazy.

 

I'm trying a new tps tomorrow and if that doesn't work then turbo swap.

[NewZed]

In Post #13 I was going to suggest that you check your FPR for a blown diaphragm. I'm guessing I should have left that comment in. Is that the vacuum line to the FPR pointed at the cold spot? Vaporizing fuel and loss of pressure regulation?

Edited August 6, 2012 by NewZed

[BluDestiny]

Yes it is exactly where the vacuum for the fpr is plugged into. about to start it and pull that vacuum line and see whats up.

 

edit: pulled the vacuum line right at the fpr and guess what? NewZed wins a cookie, gas spilled out.

 

So I'm going to try and find a cheap fpr at autozone.

Edited August 6, 2012 by BluDestiny

[BluDestiny]

Got a new FPR in the mail. I got the same exact one as it made it a remove and replace job. Took me 30min tops. Anyway car is idles prefect, starts a sec after the key is turned, holds pressure much better ( I said the old one would bleed off pressure in like 5 min).

 

So I'm about to start my cross country journey, hoping ot make it back to my home town Burbank by Saturday night.

 

I'm sure all the other parts I changed helped too though

[BluDestiny]

Just for reference this is how bad my FPR was: