Losing Faith

[cozye]

Ok Well, I got the car running. It's kind of fumbly, but she idles. However, you press the gas, it instantly dies. Any ideas?

have you gone through the FI troubleshooting procedure in the FSM ? Could be water temp sensor making it run rich. Could be a lot of things. Did you ever get a fuel pressure gauge on it ?

[FastWoman]

Hey, congrats on getting the thing running (sort of)! What did you do to get it to fire up?

When you lightly press the gas, the throttle position sensor (TPS) is actuated, and the idle enrichment is lost. That's probably enough to change the mix enough to kill the engine. You do need to go through the basic EFI troubleshooting in the FSM, as Cozye suggests. My guess is that you have at least several problems going on.

It's VERY, VERY important, before you get too wrapped up in EFI diagnosis, to make sure you don't have any vacuum leaks. I'd bet money that you do, at least if you haven't gone through and replaced all your vacuum hoses. In my own case, there was a huge vacuum leak between the intake manifold and the head. It was even drawing in leaking exhaust -- a super-EGR sort of thing going on!

Chris' suggestion of dual SU carbs is a reasonable, time-honored approach. However, a properly running EFI engine is soooooooo much more reliable. It's just getting to that point that's the bear!

[SledgehammerX]

I did change all the vacuum lines and can still hear a hiss but cannot track it down. My intake to head gasket may be gone. Hmmm, I'd love to go carb, but it's so expensive or at least when I found it

[FastWoman]

Well, to check for an intake leak, you might pull off your AFM and plug the AFM-to-throttle boot with a yogurt cup. Pull off the brake booster line, and connect a clean hose to it. Blow air into the intake manifold (by mouth), and you should feel it holding pressure, at least for a little while. You can see how fast air leaks from a known leak by disconnecting the adjacent HVAC control vacuum line (the smaller hose). A leak of that size will alter the running of the engine a bit, but not radically. I determined on my own engine that the sum of all leaks (including around valves, past rings, etc.) was much, much smaller than the leakage would be through that one fitting, so I was satisfied my engine was tight enough that its functioning wouldn't be compromised by vacuum leakage.

If I had determined there was a leak, I might have found it by blowing air into the intake, while feeling for escaping air in suspect areas. You could also shoot a bit of starter fluid in the intake, put just a tiny bit of pressure behind it, and sniff around for escaping ether. If totally stumped, you could probably "sniff" the leaking starter fluid with one of those freon sniffers, that you could borrow/rent from an auto parts store.

I hope it's not your intake gasket. That's a bugger to replace (assuming you have seized studs, which you probably do). However, if you have a big leak there, that could certainly make your engine run like @$%!.

[Walter Moore]

You can also check for leaks by spraying carb cleaner on various fittings and gasket surfaces around the intake. When you spray the cleaner on the leak it will be sucked into the intake and the engine will suddenly run "differently". It may die. It may stumble. It may surge. But whatever it does it will change, and that will allow you to identify the source of the leak.

[ChrisZ]

Sarah, I can't agree with you a, well tuned re furbed pair of SU's is pretty much set and forget and will probably give you less trouble than a FI like the kind in the 280Z

Chris

[FastWoman]

Dunno... I'm not anti-carb, but just not particularly thrilled by them. I've had lots of carbs of various types, two L-Jet Z's, and a few more modern lambda-type hot-wire EFI vehicles. Although the L-Jet Z's are less reliable and more finicky than the modern EFI systems, they've still been more reliable and better performing systems than any carb I've used. My '75 was my daily driver for over a decade, and the EFI never let me down. I admit I don't have much time/use on my '78 EFI yet, after having straightened it out, but it's running beautifully -- instant starts, even in the bitter cold.

By comparison, I've had carbs by Datsun (210), Mazda (RX-7), Toyota (Celica), Chrysler (Fury III), Olds (Cutlass), Holley, and Edelbrock -- and probably others that I've forgotten. In all fairness, the manual-choke Mazda 4bbl carb was pretty well tempered, but I didn't own it very long, and I bought the car new. The 1 bbl carb on my John Deere tractor comes closer than any of these to being trouble-free (and it's really not). I admit I've never owned an SU, though. Seems like a good design.

Sledge, if you do go with a carb system, I'd avoid the Holley conversion. I just finished rebuilding the Holley on my boat, and I'm not at all impressed with the design or build. It's cheap, though. I'll give it that.

[cozye]

Too many people ditch the EFI because they can't diagnose. Putting carbs on isn't going to make you a better mechanic, nor is it going to solve the problem. Just take a methodical approach to getting it resolved and you will get there. I'd be willing to bet you are fairly close now and could fix it without much money if any at all.

The hiss could be your idle screw is out so far to make up for a poor tune or faulty EFI part that you are hearing the hiss from air through the throttle body.

Poor fuel pressure could cause the symptom you are seeing.

I had this same issue once when I was working on my ignition, I could get it started and idling sort of, and it would die if I gave it gas. I simply forgot to plug the water temp sensor plug back in and it was running way too rich.

Go through all of the EFI troubleshooting steps in the manual. It will take you no more than an hour.

Get your fuel pressure reading to us at idle and report back.

Part of the EFI troubleshooting will be to take an ohm reading for the water temp sensor at the ECU 35 pin connector. It will tell you if that is working correctly.

Also, can you feather the throttle and get it to rev up at all? If you can get it to rev up, can you hold it at say 3000rpm ?

[FastWoman]

Sledge, did you manage to make any progress? Just wondering...

[cozye]

I'm sure he fixed it, never to be seen again or report back what it was.