rx7_freek

Help! Here's the scenario:
I've got an '81 rex that we've been working on for a while now, trying to get it to stay running after 6 years of sleeping in Michigan. I've replaced the ignition coils (leading and trailing) and tested for spark...good spark. We dropped the tank looking for a clogged strainer, blew out the fuel lines, took the horn off the top of the carb, blew the holes out and cleaned and checked the float level in the fuel bowl. We appear to have good fuel flow because when we remove the feed line from the carb and turn on the key, fuel does pump and fills a quart container within a minute.
The deal is, that we can get the car to start, but after about 20-30 seconds the rpm's drop like a rock and the engine dies. I've searched through the post archive and see that a possible blockage of the cat could be causing this, so yesterday we removed the cat and still get the same results. One thing that I DO notice is the 'Overheat Exhaust System' light is on when running...regardless of the engine temp. When removing the cat, we didn't even see the electrical connection that is supposed to be between the cat and muffler.
Is there any type of troubleshooting list out there where we can eliminate more possible causes of this malady? And/or does anyone have ANY more ideas here? I'd hate to have to start blowing money, buying things we don't really need to replace.
Help! Thanks!

JD
p.s. We are planning on checking the compression next weekend.

Manntis

I was going to suggest inadequate air supply, but with a carb'd engine that rarely happens. Surely you'd notice a clogged filter.

rx7_freek

Actually, right now, we don't even have the air cleaner attached...air flow is not a problem.

Rotor13B

6yrs? Maybe your floats are bad? Flooding?

rx7_freek

Well, when we took the carb apart, we did a measurement of the floats. Can't remember the exact specs that were in the Chilton's, but they checked out okay, although when I look through the site glass at the front of the carb, it does appear to be a little high.

Hereonout

Hey man same here, but mine ran for 1 day, went to go to work the next morning and its been doing what u say for the past 2 months....im going to get a used pump today......pray.

rx7_freek

Ok guys...I found something last nite that is 'wrong', but I'm not exactly sure what it is.
The item in question is below the windshield wiper fluid container and is attached to the passenger side strut tower. The black circular object that has two hoses coming from it that attach to the fuel system via brass tubes. One of the brass tubes runs across the top of the engine compartment to the driver's side, then down and back to the fuel feed assembly somewhere...I didn't take off the fuel pump/filter access plate to see exactly where it goes. The other tube then connects to a rubber hose that connects below the carb, driver's side.
I couldn't find any reference to this thing in my Chilton's but figure it's not supposed to have a 1/2 inch x 1/4 inch hole in it (chewed by mice)...probably breaks a vacuum in the fuel system?

I'm going to drop by the junk yard tonight and scavenge the part off an '83 that I know is there, but would still like to know WHAT it is

Pics attached:

inittab

It's the charcoal canister. From what I understand it helps remove gas fumes. Mine was disconnected for a short while and the car ran fine.

djmickyg

yeah like inittab said that ur charcoal canister. and it removes the 'bad' part from the fumes, as charcoal is a nutral filter and pumps the clean air back into the gas tank so it doesnt polute the air. but u dont need that for the car to run, mines disconected.

when u start ur car, are u starting it by just pumping the acclerator and turing the key or are you pouring some petrol down the carb first??

does it die when u try and press the accelerator or just on its own??

it sounds like a fule delievery problem, in the carb.

rx7_freek

I start the car by pumping the pedal 3-5 times and full choke. It starts up usually after about 8 cranks, maintains 3-3.5k rpm and then after about 10-30 seconds, just DROPS...really fast, no sputtering. I have tried pumping the gas WHILE it's dying, to no avail.
Even though the pump appears to be functional (see original post), could it be the thing is operating intermittently? Has anyone used one of those 'universal' pumps? What is recommended for fuel pump replacement?

error402

When it just drops, does the choke cable go back in before or after it starts to shuts off?

-Error402

MyRxBad

I know this sounds stupid, but check the level of gas in the gas tank. Maybe there is a break in the fuel pickup in the tank. I helped a guy out once, we couldn't figure it out. The car would start and then die out eventually. No clog filter, we could siphon fuel though the lines (in the engine bay) and it turned out one he filled the gas tank it ran fine. Fill the car up w/gas and try it agian. *Can't hurt*

rx7_freek

Error 402: The choke goes back in AFTER the engine dies...I know this for sure because I've got my hand on the thing holding it out. I don't think I NEED to do this, but do just for thoroughness I guess.

MyRxBad: I guess I could try that...right now we've only put in 5 gallons figuring that would be enough for what we want to do. Guess I'll have to make a few trips to the gas station with the gas cans!
Thanks...I try that....keep em coming!

V8kilr

hook up a voltage meter to the coils to see if voltage is dropping off at the same time idle falls off, if so there may be something electrical shutting down sprk because it thinks the engine is overheating,
the choke should not return until
1- the car is heated up
2- the car is turned completely off

if the vehicle stalls the choke should stay out, its magnetic

the problem sounds electrical

what happens if you hold the gas in before it dies?
will it still die regardless?

I have seen that before but at the moment I cant remember what the hell it was.
but I remember it was electrical and it was also an 84 which is still a 12a but computer controlled egr stuff

the exhaust gas temperature sensor maybe grounding itself out, if its not hooked up then look more over towards the driver side and right across from where the cat was,
it looks kinda like a steel braided spark plug wire, check it.

let me know if anything helps, if you lived closer I would come by but your on the other side of the state.

rx7_freek

Well, not 'exactly' the other side of the state...the last Wings game I went to it took me 1 hr 45 m )

We do have a voltmeter and have used it to check return voltage from the alternator...that looked good anyway. Will try as you suggest and monitor the stalls.

Yes, if I hold the gas in it will die regardless.

I wouldn't doubt that this is an electrical problem, because we've had to graft an '83 engine wiring harness (to my '81) to repair mice damage. We grafted it just forward of the ECU (broad-many pinned) connectors on the drivers' side aft of the strut tower.
I do have both wiring diagrams for the '81 and '83 so we did have a reference, but they didn't match up exactly...couldn't have been THAT easy )
I'll check out the things you've mentioned and study the diagrams again...maybe there's something we missed.
Thanks!

V8kilr

does it make a funny noise when it stalls?

rx7_freek

No...no particularly funny noise...it just...dies.
When I press the gas in while it's dying, it sounds throaty...like it's getting gas, but is not firing.
We'll definitely do the voltmeter check over the weekend...also planning on a compression check although I don't believe that's my problem, but would at least provide a 'feel-good' about THAT anyway if it checks out ok.
Any tips on checking compression on the rotary?

V8kilr

if the compression is that bad it would even start and run for the 20 seconds or whatever it is.

diabolical1

iTrader: (3)

i just read through this whole thing. just to recap, to see if i got everything ...

- the car starts on choke, it runs fine for 20-30 seconds and then it dies
- you checked the tank
- you wired it with an '83 harness
- it dies even if you try to pump the gas

how has the filter checked out? did you replace it?
well ... my initial vote is that the pump is about to drop dead. i know you said that it fills a quart in about a minute, but at that point it's pumping without load - so it could feasibly seem fine while it's really not.

there's no need to check the compression (unless you just want to get numbers), v8kilr is right, if the compression was a problem here, then the car probably wouldn't run at all.

are the plugs new? if they are, then check them to see what they reveal ... a lean condition, perhaps. assuming that your EGT sensor is working correctly, then it would support a lean condition (i.e. lack of sufficient fuel)

that's my 2 cents based on the info

BrianHeston

My car acted much the same way. Sometimes it would die after a very short period of running. Other times it would idle forever and then die when I tried to actually drive it. It turned out to be bad needle valves. They weren't sealing properly, even though they looked perfect, and it was flooding out. They're cheap, and it's a quick and easy fix. If that's what it is, you'll kick yourself for not checking them sooner, I know I did.

I may be way off base, but hey, ya go with what ya know right?

BrianHeston

marshp

could it be a fuse?

rx7_freek

Ok...yesterday we followed V8Kilr's advice and hooked up the voltmeter to both the leading AND trailing coils(separate tests) from the positive sides of the coils to the negative terminal of the battery. There was NO drop in voltage when it dies, so I've got to think the problem is not electrical. I guess the next logical step would be to rebuild the carb...Now just to find a rebuild kit and some chem-dip. Although we did take off the horn and check the floats/needle valves, like Brian says...they could look fine, but not be.
As for the plugs, we haven't yet replaced them yet because on examination, they appear 'like new' with no build up at all.
I may just go ahead and buy plugs too, to put my mind at ease about that anyway.
Thanks for the advice...I'll keep this thread up to date.

JD

claytonjh1223

my car starts and doesnt idle and makes an awful hissing noise around the carberator and dies after 5 seconds iv moved the idle rebuilt my carb spark plugs are old and its burning coolant bad its pissing me off i have been working on this for 3 months all help is apreciated jc

Dcrasta

I would check for vacuum leaks. sounds like a big vacuum leak is getting both of you.

That rats next its easy for a split vacuum line to hide in.

Wankelguy

Sounds like your float bowls are running dry. The fuel system on these cars seems to be the Achilles' heel.
My '80 sat in the desert for ten years before it was given to me. I had to completely go through the fuel system, including installing a new pump. How long after it dies are you able to re-start the car? Also, the carbon canister mentioned does more than just get rid of fuel fumes, it keeps the tank purged so that it is in an air-starved condition so the tank doesn't blow up when the sending unit inside the tank arcs, which is normal. Have someone observe the fuel level in BOTH float bowls and see if one may be running dry. The rear one can be seen with an inspection mirror. Your problem COULD be as simple as a blocked fuel filter, or the little fuel inlet screens in the carb may be gummed up as well. You need to determine whether it is starving or flooding to be able to diagnose the problem. It doesn't sound like an electrical problem to me, seeing as how you checked the voltage to the coils, good work. -WG