dankekong

iTrader: (2)

Background:

1985 GS, pretty stock. 2 brand new coils, 4 new plugs, new yellowtop battery, starter, alternator ground and positive cables. Definite exhaust leak at manifold, causing backfiring on decceleration.

Problem:

At full throttle in neutral and under load car would stutter, bog down a bit, but if I let off a touch it will pick up more speed/rpms and be smooth.

Also, recently started losing close to 50% of its power at random intervals, regaining it with some sputtering. Gas pedal to the floor to go 45 mph at points when it loses power. Also, idles at about 500 rpms when power is lost, but again regaining it and climbing back to idle.

A few days ago: intermittent power to starter, yet lines are new as of a year ago. Maybe they have come loose....at least the positive cable may have.

2 fuel filters in the system, both brand new. Any help/advice is welcome

7aull

iTrader: (2)

A crapped up fuel tank could be plugging up either at its exit point (which is meshed) at the tank or the filters. have you re-checked the filters? Do you notice the problem more when the tank is below 1/2 to 1/3 empty - or is it all the time. In my experience, the tank plugging/power loss got worse on low fuel levels.

Others may suggest carb issues (valid) but on a 25+ yr old car, esp if its spent long periods sitting, it may be time to pull the tank and get it chem-cleaned (rad shops will do this for $65+) then re-lined inside. POR15, for one, makes a kit to do this for... $30? por15.com. Not a difficult job...

'Luck!
Stu Aull
80GS
Alaska

dankekong

iTrader: (2)

The fuel level in the tank is irrelevant to the problem I'm having. However, I took a look at the old fuel filter and its pretty clean, nothing there to suggest a rusty or gunk filled tank anyway. I may have to go over my starter/battery wires again and see what happens, but there has to be something with the fuel also. Adding the 2nd fuel filter didn't cause any problems that I know of, but who knows.

rxtasy3

iTrader: (2)

impossible.

dankekong

iTrader: (2)

You're trying to tell me that I can't be having this issue when in neutral and when under load? These forums are designed to promote advice and progression with posts from members, not ignorance and unhelpful posting

t_g_farrell

iTrader: (1)

If you have sorted the fuel system and your sure theres no vacuum leaks then
I would start looking at the ignition. When its running at 50% power and
only getting to 45 that hints that it may only be running on the trailing alone.

dankekong

iTrader: (2)

Ignition seemed to be good....new coils and igniters not helping. Maybe the distributor could need some attention...I don't know

780rx7

still sounds like it's starving for fuel to me. Did you try taking out the second filter and trying running it? Also, I don't suppose there is any chance you have water in the fuel tank? I had this problem with my street bike once, exact same symptoms. I ran gas line antifreeze in the tank and after a while the water ran through and the power cleaned back up. Try adding seafoam to the gas tank? just some thoughts.

dankekong

iTrader: (2)

I had the problem before the 2nd filter, but i could try it. Seafoam looks good but I dont know if it actually works at all. What would be the best way to clean the tank without removal? U think seafoam?

RustyRacer

I think you need to clarify when these things are happening.

The reason rxtasy3 said impossible is because in neutral your car has no load. Did you mean at
1. full throttle
2. or in neutral
3. or under load?
which would be all the time


Are your 2 fuel filters in Series or Parallel? If they're in series and you're WOT then yea, you're going to run out of fuel, but if they're parallel then you've got twice the capacity available. Do you have one of those little filters by the carb? That thing can run out faster then it can fill back up.

How can you say you're not sure Seafoam works?

Seafoam won't necessarily clean your tank, and if it does you don't want any of that crap going through your fuel system. Drop your tank and get it cleaned out at a radiator shop, expect between $75 to $125. Its two straps and some hoses, just label and mark which ones go where. And get new fuel filters in Parallel.

dankekong

iTrader: (2)

No one seems to understand the difference between being in neutral with the pedal to the floor, and being in 5th gear, pedal to the floor.....that's the situation. Constant backing occurs but that could be the exhaust leak i have at the manifold. As far as moving my fuel filter, where would you suggest it be located? Right now its in series with the other filter on the supply line.

t_g_farrell

iTrader: (1)

Ok, did you do a pressure and flow test of the fuel system? You know check the
pressure with a teed in guage. Check the flow by timing how long it takes to fill
a gallon bucket (or half gallon) form the hose going to the carb. These are pretty
basic tests but should verify a lot of the fule system.

Still sounds like an ignition issue to me if its not fuel.

wankel=awesome

Could also be a combination of problems. It does kinda sound like a supply issue though.

RustyRacer

We understand the difference, but the way you wrote it made it seem like you were saying in neutral under load, which is impossible.

https://www.rx7club.com/1st-generation-specific-1979-1985-18/dual-fuel-filter-mod-528445/

Try this first, its the cheapest and knocks out one issue.

You should still check your timing, and get your tank cleaned out if your filter has junk in it. I'd suggest getting the clear plastic filter so you can see if there is crud in your tank. Ditch that filter by the carb, run the parallel in the back. Your carb has filters as well.

I agree with you TG but this happens at WOT, it wouldn't matter in the driveway to test the flow, but it'd be a good idea to test if you can.

gsl-se addict

iTrader: (3)

I think he means:

"At full throttle, in neutral, and(or) under load....."

Is this the case (happens at full throttle in the drivewway) or not? Depending on when it does it, it could be different things.

If it is fuel, thing would have to be pretty bad to cause it to choke out in neutral. The engine needs very little fuel (even at 7k RPM), if there is no load.

I would check fuel volume 1st. This is a little hard to do on the 84/85 12A cars, though. The reason is there is a relay that causes the fuel pump to only run when cranking or the car running. You could run 12v to the pump for the test or remove the spade connector from the starter and hold the key to 'START' for the test. Put the fuel feed line (at firewall or at carb) into a gallon jug. Do whatever you need to do to run the fuel pump, and time for 1 minute. There should be a little under 1/2 gallon in the jug when you are done. If it is much less, then you either have a clog (pickup tube, hard lines, etc.) or the pump is dying. This is a pretty quick test and will tell you a lot about the condition of your fuel system.

Once you know if the fuel system is good or not, then look at ignition and possibly the carb.

Did it run fine before? Any changes or work done prior to it acting this way?

dankekong

iTrader: (2)

No changes or work done. I may be leaning towards a dirty tank but its hard to tell. Timing is perfect and ignition system (other than distributor) is new. It sat for 3 months before I replaced the coils i needed to. Maybe thats the issue.....needs a cleaning. I may try the parallel filter setup, but it wont fix the problem. Maybe the pump is weak, and I will try one of the tests suggested to see how much gas its pushing.

Thanks guys, I will keep ya posted

rxtasy3

iTrader: (2)

what i'm saying is it's impossible to rev in neutral AND be under load. there's no load on the engine free reving in neutral. and fyi, i'm far from ignorant and unhelpful. i've helped quite a few on here over the yrs.

dankekong

iTrader: (2)

Ur right...it isnt possible to be in neutral and to be under load....thanks for the heads up. Seriously, u shouldnt assume people are so ignorant.

dankekong

iTrader: (2)

Ok here is an update: when driving under normal conditions and the power is suddenly lost, a couple of times the idiot lights flashed on....very quickly....when the car started to rev down. It wasn't stalling, or at least, wasn't going to stall. Makes me think the ignition is the problem, not fuel, because why else would the car think it is off for a split second? Seems to me like that would be an ignition issue.

What do you guys think?

74RX4

iTrader: (10)

Make sure the negative battery terminal, ground point on inner shock tower and connection to the long starter bolt are clean and tight. Clean (scrape) the Main fusible link terminals and the terminals in the box that holds it.

dankekong

iTrader: (2)

Thats a very good idea, but I did all of that about a year and a half ago. I will definitely go over it all again, including the positive cable to the starter, hopefully something has come loose and needs to be tightened or redone. Thanks for the tip, hopefully it works

dankekong

iTrader: (2)

So I went over both the negative and positive cables including the shock tower ground and it seems to have helped. Also tightened up the alternator connector/ground which was a little loose. Seems to have helped, but haven't taken the car out yet. May drive it later and see what happens.

dankekong

iTrader: (2)

All for naught, no fix...still intermittent power. I will be checking the plugs tomorrow to see which ones werent firing, if thats the case. When I drove it, like before, it had maybe half power and would stall everytime in neutral because the rpms would be too low to run on. Seems like its only firing on a couple plugs. Gonna check to see which ones....but if all 4 are clean, then I may have a clog in the fuel system or a dying fuel pump. Who knows

dankekong

iTrader: (2)

Just pulled the plugs. After the last run, when it was NOT running right and stalled out when I parked, the trailing plugs seem to be darker than the leading plugs, but not by much. It does seem like all 4 were firing.

Started it up when I put the plugs back in...it warmed up and when I came outside it was off so it must still be running the same way it was. Pulled the plugs, all 4 seemed to be firing but it's hard to tell if the problem is from lack of fuel supply or from weak plug firing. They werent dripping with gasoline, but they werent gold/tan either. Somewhat blackened but not fouled I don't think

Seems like a fuel problem? Maybe the 25 year old, original, fuel system needs some attention?

780rx7

My recent "searching for days" post went through some of the electrical issues I have been having recently. The big eureka that I just had was a loose ground to the fuel pump. Most of the rear electronics including the fuel pump and fuel level sending unit ground to an eyelet that is attached to the body inside the rear hatch at the hatch switch. You just need to remove the screws that hold the rear curtain cover inside the hatch and it is right there. THis black wire that is grounded to the body was loose on our car causing an intermittent fuel loss problem because the fuel pump wasn't getting enough electrical power. Not sure if this has anything to do with your problem, but might as well take the 10 minutes to check this ground. Also, turn the key on and listen to the fuel pump without starting it. It should be a steady audible fast clicking sound (if mine is correct). If it is more a dull buzz, it is not getting enought power.

Good luck!