85 GS Loss of power/backfiring when warm
 

First let me say that this is a wonderful community, I wish I could find the time to contribute more, the posts here have helped me fix my rx7 so many, many times.

But this time, I'm unsure even after searching and I apologize if I did miss a similar problem somewhere in the archives.

Vehicle: 85 GS Stock Nikki with 134a A/C conversion
Mileage: 87,455 (body and engine)

Past Problem:
I always used to have a strange issue where the car would idle and drive fine, but sometimes when I would start to touch the pedal, it would just try to die completely. This would happen in once out of 20 tries to the pedal, but it started to get worse so I did the change below.

Recent Changes:
After I changed the fuel filter, this problem went away and the car was driving much better, I didn't know why I didn't think of this before. I also ran some Seafoam in the gas, about a half bottle to a full tank.

New Problem:
Now the car seems to struggle more with starting and not immediately after changing the fuel filter, when warm, the car idles terribly (below 500rpm) and is hard to rev and after being brought to 6k rpm when it returns to idle is backfiring a bunch. The car also has barely any power. When the carb is being choked, it idles and drives fine, no problems at all; just when the semi-auto choke disengages do I have the above problem.

This problem almost immediately happenned, though it took a few miles where it was getting weaker and weaker to the point that I had to rev the engine and slip the clutch to get it moving.

All lights, temps, and pressures seem normal from the gauges.

Carb was rebuilt 4 years ago.

I did change the spark plugs and while the old ones were pretty bad, it did not fix the problem.

Things I did not notice:
No big banging noise from the engine. No smoke of any kind coming from the exhaust, even after sitting overnight.

Non-Important Stuff:
I love my rx7 very much and I very much hope and pray to the apex seal gods that my problem doesn't involve a rebuild.

Of course this problem happened the day after a teenager who was texting made a left hand turn into my DD and totaled it... also he didn't have insurance.

In advance... thank you to anyone who has any sort of advice about this, I greatly appreciate your help!

I'd say you still have a fuel flow issue because it sounds like its running lean when the choke lets off. Also
running fine with the choke on is almost always a good indication of fuel delivery issues.

I would take the fuel intake hose off at the carb and put it in a bucket and measure the flow rate. See if
its below what the FSM specs call for (find FSMs here Foxed.ca). If it flows ok at idle then I would
suspect that theres some gunk in the carb. Since this isn't a DD, it could just be gunked up from sitting
too long with old gas in it. You may need to at least pull the top off the carb and clean it with carb
cleaner. The other thing you can do is remove the fuel inlet hose barbs and make sure the screens are
clear in them.

So, I should do this part?

This would prove whether or not the fuel pump is working correctly, if it is then..

Then try using some carb cleaner and finally check the screens?

Thank you for your response!

Yes, exactly. If it only did this on acceleration, I would question the pump but since it does
it at idle also, I suspect its not the pump, but its easy to rule it out this way. Always work
your way from the source of the fuel to the intake, same for spark and air. It needs all 3
to actually work.

You said you put seafoam in the tank, was that after you replaced the fuel filter??

If so, replace it again. Seafoam has a tendency to loosen up crap in the tank, than plug the filter

Yes, I did put Seafoam in; before I put in the filter. AND after... Now the tank is running 16oz to a full tank. I am also premixing.

Today I tested the pump's output and it was normal.

I used some carb cleaner and then went for a short drive which towards the end it was back to having no power at all.

It is also kind of strange, it seems like the engine has really good power when the choke has just disengaged and the engine is warm and then it slowly gets worse and worse till the engine is at a crawl.

I'm starting to fear that this is a coolant seal issue. Does anyone know if coolant seal problems happen in this manner above?

I am going to replace my fuel filter again. Then investigate further whether or not there is a problem with the carb's fuel line. There has to be something that changes with engine temperature that I am not knowledgeable with. It just seems like the car is being strangled of all power.

Thank you again for all of your responses, my car greatly appreciates it. I put a halloween picture of my rx7 and my wife's 90 miata below.

Pull that filter and look at it closely,tap it on a paper towel and see what comes out. You may need to go thru carb but i wonder if there's a bunch of garbage in tank getting sucked up to fuel pickup sock and not allowing any volume of fuel flow. You shut car off,it cools off,crap drops off pickup til you start to drive it some. Rinse & repeat. Coolant seal failure almost always coincides with loss of coolant & steam/white smoke from exhaust.

Good point. I'll keep at it, thanks again!

How much coolant would be lost from a seal failure? Over the past 3 years my reservoir has gone from the middle of the tank to the lower marker. Would that be enough? I do not really see steam or white smoke though, maybe a faint amount and I do not notice it when the car is warm and is being strangled for power.

I wouldn't get too worried about that little amount of coolant "loss". Are you checking the overflow bottle the same way each time. When engine cools,radiator pulls coolant from bottle to keep system full. When at operating temp level of coolant will rise somewhat. Top up bottle to cold line with 50/50 mix,drive car til fully warmed up and note level of coolant. Look at it again when cold so you see what's normal,if there's no rise/fall of level in bottle indicative of air/coolant leak.

After exhausting the fuel delivery issues you may have an ignition issue. That said, make sure the fuel
delivery is good.

The igniter for leading may be going bad once it gets good and hot. This is typically how they fail. If its
just the trailing that failing you won't notice it but if the leading is failing, it can act like you are seeing.
The quick test is to just swap the leading ignitor for trailing and see if it all works better. If it does, then
theres your problem.

The reason I say this is because of what you said in the last post about it running fine even after the
choke lets go for awhile but then it degrades. This is a typical ignition failure mode. Runs fine until
the under hood temps get good and hot. Also gets worse and worse over time until you just can't keep
it running. Its similar to fuel issues except fuel is usually constant over temperature.

100% agree,was going to suggest that in subsequent post. Didn't want to overload op with too much diag info at one time.

Great idea! I saw posts regarding this test, but I was assuming that the problem was related to my recently replaced fuel filter. Good thing that test is rather easy to try out. I'll give it a go and see what happens.

You guys are great! Once again, thank you and let's hope for the best! I'd buy everyone a beer if we find the fix!

Darn... no luck. I cleaned the leads and swapped the ignitor coils and it still loses power after about 15 minutes of driving and it gets horribly backfirey and begins to be very hard to drive with little to no power.

I adjusted the fuel/air mixture and the idle throttle some and it seemed to help a little. But it will still drop into a mode where it just acts very very poorly.

Thank you for all the help everyone, I really wish I could figure this out.

Have you rechecked the fuel filter, is it possible you could retest the fuel pump pressure/volume when the car is acting up. I realize this may mean having tools on hand,maybe on side of the road or in a parking lot.If you're lucky,at home. Window of opportunity may not be very long to diagnose running problem so you have to be ready.
Suggest as car has reached point of acting up-don't shut it off or keep it running til the moment you're ready to test,then shut off and immediately test pressure/volume to eliminate as a cause.

Did you swap the ignitors or coils because you said "ignitor coils" so I'm cornfused. You swapped the
2 modules on the dizzy right?

I swapped the coils... should i have swapped the J109s? The coveted J109s? Like in the picture I attached?

Good idea, I'll bring it to the point when it's acting weird and then do the test again. I'll get back to everyone once I did. Thank you again everyone for the help!

You did just say "igniter" I guess I should have paid attention better... I just assumed the coil because it is less of a solid state problem and I assumed that solid state stuff either works or doesn't. Also in the FSM it states that the coils need to be measured at temperature, I didn't think the J109's would be affected by temperature in this way.

Yep, the j109 ignitors. Typical failure is that they overheat and degrade in performance. So give it try
swapping the leading and trailing j109s. Its easy to do.

T G Farrel and GSLSEForme... if you find yourself in Illinois, near Chicago. You both get some beers from me. It was the J109, I very much appreciate your help.

I was able to doubly verify that this was the problem because after I switched them, the tach would act up and go to zero periodically which is a sign of a bad J109 on the trailing igniter.

Thank you again RX7Club! You saved my RX7!

Good to hear Quel and it only took 20 posts to resolve it, a new record. LOL

Tim

You need to bring it down to DGRR now that its running.

http://www.dealsgaprotaryrally.com

My 85 started showing similar symptoms, I swapped my igniters around and it behaved much better.

I'll be completing my HEI Direct Fire Shortly.