Requesting help with a tricky problem!?
 

My pretty much stock 84 GSL is running very well except when I try to acccelerate hard, up hills or passing at high speed. Then it tries to die, losing power until I let off the gas and give it a few seconds to recover. Then it runs fine again until I'm pushing it too hard out on the highway or accelerating up a hill. It also goes through a stalling phase when it's first warming up on a cold morning, which is a little below freezing here in northeastern Georgia.

I've checked the fuel pump and it's a recent replacement that's pumping strong and steady (I used it to pump about 5 gallons out of the tank, looking for irregularities or signs of rust or water getting to the carb, but it ran clean, strong and steady during this test, with no water at the carb). I did find some water in the fuel filter, so I replaced the filter and added some dry gas, but this didn't change the stalling behavior. I've been watching the replacement filter, which has collected a few mls of water, but I don't think it's enough to cause this problem.

I've also systematically changed the plugs, plug wires, cap and rotor, both ignitors and both coils, still with no change for each of these replacements. Wiggling the ignition switch when the stall is happening doesn't make any difference.

It's a tricky problem because the car runs fine at idle and most driving speeds, the secondaries kick in and it accelerates normally at lower speeds. In fact it's quite driveable if you're careful not to ask it for that extra power at high speeds. When it's idling in the driveway everything seems to check out fine.

Anybody got any good ideas? Thanks!

Ray

check the screens on top of the needle and seat in the carb and I think some had a screen in the fuel banjo fitting where the rubber line hooks to the carb. also the float level will make it do this.

Can you verify that your accelerator pump is working correctly?

How can you do this?

If the accelerator pump is faulty when you accelerate the the engine you open the throttle and let in a huge quantity of air without fuel being pumped in to compensate. And the circumstance you describe are normal.

any idea what the flow rate is on that pump? sounds like the carb is running out of fuel.

Yeah, do a proper volume and pressure test on the fuel.

To check accel pump. Don't even need carb on for this, there should be if memory serves me (too much Iron Chef) two little ports that come from a single diaphram pump that spray into the primary chokes.

Float level look at the side (nikki decided to make little windows for you)if its at the line or lil more then 1/2 way you should be set.

Now here's the thing... are you over richening it too fast or leaning it out?

Or hey maybe you had Mech secondaries and you didn't even know it :P

Wow, seven responses since I posted this request at 10 pm last night - you gotta love the RX-7 community! I agree it seems like a fuel problem, but I know from experience and what I hear that most "fuel problems" are electrical.

I don't think it's the accelerator pump, there is no hesitation when starting to accelerate at all speeds, including doing 70 on the highway. It only starts to stall out if you hold the gas down and push it for 5 seconds or so, usually right around 80-83 mph (it will cruise steady at 80 if you bring it up to speed slowly, but occaisionally goes into the stall if you start going up a grade or try to pass some semis). Also I had the accelerator pump problem on my other GSL and the symptoms are very different, the faulty accelerator pump gives a short hesitation when you first give it the gas.

I didn't do the fuel pump test "by the book" but I did do my own backyard version, filling up a 5 gallon gas can in about 20 minutes. My pressure test, holding my finger over the end of the hose, showed I could squirt the gas about ten feet. So I don't think it's the pump, but I do have an almost new spare from my other GSL that I could swap in, maybe I'll do this on the weekend.

At this point, if it's not some electrical gremlin (like one of those vacuum activated valves that makes up the rat's nest??) then I think numan2 and Marek have the right idea, there's a problem in the carb. It has vacuum activated secodaries and these kick in nicely, giving real good accleration at lower speeds. In fact I can floor it on a level run and it will accelerate right up to 80 without a problem, using a lot of gas in the process. Another reason I don't think it's the fuel pump.

I'll check the float level (forgot about those little windows Marek, thanks!). I haven't been messing with the fuel adjustment or idle, both of which were working fine before this problem showed up. Also, please remember, other than the highspeed stall problem, the car is running very well, gas mileage is around 23 mpg.

So I'll follow numan's advice and crack open the carb, looking for those little screens. Still, I hoping it might be something a little more obvious (like water in the gas, bad pump or ignition parts and all those other things I've already looked at). Is there some kind of electrically operated high speed fuel circuit?

Again, thanks for the help Guys!

Ray

OK, I looked at the carb, there's gas in those little windows, both sitting and idling, on both sides it's a little less than half way up the window. Is this how it should look? The problem is gettting worse on cold mornings, but after it warms up it runs good (except at high speeds over 79 mph) so I've been using it for the 110 mile commute this week without too much trouble. Still, I need to fix this in case I need to embarass some mustangs. Any suggestions? I'm thinking about pulling the tank and redoing the fuel pump this weekend, the carb would be next.

Ray

here's a test to try run the car hard until it dies out once it shuts down turn the ignition off and cost to the side of the road open the hood and look at the windows again. What this does is doesn't allow the fuel pump to replenish the bowls if they are running dry you will see no fuel in them. If you see fuel in them then most likely it's not fuel related issue.
you stated you changed the fuel filter did you change the one under the car or the one in the engine compartment? most of the time the one that's full of crud is the one under the car.

where's the fuel filter in the engine compartment? I didn't even know we had one there.

Thanks numan, excellent idea, I'll give it a try on my home from work today. My 84 GSL doesn't have a filter in the engine compartment, although I did put a plastic one in for a few days just ahead of the carb to see if I could catch any water or dirt getting past the primary filter that's under the car, between the tank and fuel pump (this didn't happen, the gas in my engine compartment filter was always clean and dry). Actually the engine compartment filter was kind of neat and seemed like a good idea, but I took it out because I didn't want to create a possible gas leak later, when I wasn't watching it so closely. Wouldn't want to toast my engine, heh heh.

Ray

I've always run a filter just before the carb....cheap insurance if there's any crud in the line or the pump starts making debris.

OK I tried to do the turn off the key test when it starts stalling out, but wouldn't you know it, now the car won't stall. 85+ going up a hill, no problem. The thing's been coughing and sputtering at high speed for the last few seeks, more than 1000 miles and three tanks of gas. I've tried about a dozen different things to fix it, and now it seems to be resolving its issues all on its own. You gotta love those Mazda engineers.

Ray

Ray, how long has it been since the carb was rebiult? My 83 had the same problem until the carb was replaced with a fresh rebuild.

Definately a possibility Jays, swapping or rebuilding the carb is next in line after I swap out the fuel pump and take a closer look at the gas tank this weekend. Luckily I have a complete running parts car so I can swap parts when needed. But right now the dang thing is running great, maybe if it ain't broke I shouldn't fix it?

Ray

Dude, she's just running great until you let your gaurd down, lol.

I just read in the racing beat catalogue that if you have an after market carb the stock fuel pump might not deliver enogh fuel. That would explain the full throttle drop, but not realy the high speed part. Do you have an aftermarket carb?

FUEL LINE FILTER that solved the same problen in my car.

Nikki carb, filter's fresh. But you're right DriftFB, sometimes it's just not getting enough fuel, like the pump can't keep up. Problem is, somedays it's fine, other days it's bitchier, needs to be warmed up nice and slow; then she's fine. In fact, this problem has been alot like trying to figure out a woman who's in a mood, with something on her mind.

If it gets a little warmer out today, I think I'll go out and switch out the pump, the replacement that's in there now (which seems to work fine) was jury-rigged by my brother-in-law (hey Vinny, you out there) - he used some plastic binding straps instead of putting it up in the cradle where it belongs.

Hey Bob, you still kicking? Must be good to know GW won't be screwing with you all's social security. I'm a little worried, sounds like there won't be anything left for us prime-time baby boomers!

Ray

It's a good idea to replace ALL of the rubber hoses in the fuel system. Sometimes these old hoses swell up on the inside and block fuel flow. fix everything but this and you will still have the problem. Take it from someone who knows. besides, it's a cheap fix. Good Luck.

James, you may be onto something there. This problem just won't go away. Last week I thought it did, and no sooner than I reported this happy fact on the forum, ithe problem returned, on my way home from work last Friday. So I went ahead and put my spare fuel pump in last weekend and, viola, problem fixed! It ran great for 5 days, about 250 miles and a tank of gas. Then, a couple of days ago, guess what, it starts cutting out at high speed again, just a little at first but now, three days later, it's become a real problem (I really had to nurse it into work this morning).

It's really weird, cruising at 70-80 mph, it starts to cut out like it's starving for gas. I can quickly "fix" the problem by simply putting it in neutral, turning off the key for a few seconds, then turning the key back on and popping the clutch in 4th or 5th - it starts right back up and runs fine again for 10 or 20 miles (although this reprieve seems to be getting shorter, but we'll see how she's feeling on the way home from work today).

So yeh, I guess the next thing is to take out the tank, clean things up (I am still getting a bit of water in the filter) and, as you suggest James, replace any suspicious hoses (might as well do them all while I'm at it). The problem is, I'll bet you anything that after all this work, it will run just fine for a few days or even weeks, but then the problem will come back again.

Then I guess the carb is next. (But I keep wondering about electrical gremlins, given the fact that turing the key off and back on fixes the problem so quickly).

Good thing I enjoy working on this car and we have a nice weekend coming up! But any advice sure would be appreciated!

Ray