Tacol0ver

Hey there!
I just got a 1984 rx7 fb targa top (auto, sadly) for a very decent deal with low miles.
The seller told me about stuttering problems but claimed them to be fixed. Gave it a spin and had no problems whatsoever.
Until I got the car up to 65mph when the car started stuttering. First a lack of power, as the rpm stopped and stuttered after reaching 60-65mph and slowly going down until the engine completely stalled. After that the car would fire up, but start stuttering at 50, then 40, then 20 and eventually just not fire up. Funny thing is that on neutral the engine has no problem revving up to redline, being able to hold down the power and go back to idle. Occasionally stalling but usually just fine. The owner stated that he drove it as a daily for a year before leaving out of town and coming back with these problems.
took it to the mechanic where it had the fuel tank cleaned, fuel pump replaced, and fuel lines cleaned. I was told it was good, but the issue is still present. Any ideas as to what it might be? Carburator? Electrical? It is to be noted that it has an ignition box bridged to the key, and the ignition and starter are done with the box, with the key being only useful to unlock steering and give full 12v of battery. I just want to have an Idea of what it might be before asking for a partial refund from the mechanic.
thanks y'all, and I hope your deeper knowledge can help me!

t_g_farrell

iTrader: (1)

Whats the ignition box? Hows it connected? Are you still using the stock ignitors on the dizzy for ignition?

If you were all stock I would say your leading ignitor is failing and as it heats up it gets worse. Your symptoms match that to a tee. With the other ignition box in there its hard to say without a lot more details.

Tacol0ver

I think this might be the problem. Is there any problem in using the trailing ignitor as the leading to see if the problem subsides? I have to wait for the other one to come in and want to check if that fixes the problem

Toruki

The ignitor for the leading and the trailing are the same part number in a stock setup. So if you are stock then yes you can swap them.

t_g_farrell

iTrader: (1)

What ignition box? Got pics? Still don't understand what you have there.

Tacol0ver

Oh I'm sorry I misread your post.
It has one of those black rocker switch boxes, that has the ignition and starter wired into it. The distributor is all stock, and that box came like that when I got the car. I assume to avoid getting a new ignition switch. It attached a picture of one that looks the same. The key also allows full 12v from the battery, as if I start with the box only it only does so with a lower voltage, but it will run for a bit.

I switched the leading and trailing ignitors, and now whenever I floor the gas from a standstill the rpms drop to a stall, something it never did before. I will try my luck at fitting the gm ignitors, before messing with the wiring of said ignition box and eventually the rest of the ignition assembly

Tacol0ver

I just changed the ignitors, and it is a little better but I'm still having that major stutter at the 40 mph mark. I guess I'm going to have to start looking into the whole system 😅

Maxwedge

iTrader: (1)

Forget "mph mark" and pay more attention to rpm (the engine doesn't know or care how fast the car is moving). That being said, idling fine but then sputtering out a few miles later is a classic sign of junk in the fuel lines. These cars are approaching 40 yo and the gas tanks rust and flake internally. The little rust flakes clog up the filter and the carb. This is just the case with old cars (rx7, mustang, dodge omni, whatever). I'd look into cleaning and flushing out the fuel system.

t_g_farrell

iTrader: (1)

What Maxwedge said, you need to clean up the fuel systems and carb then chase down any electrical gremlins. I'd also ditch that box and go back to the stock keyed ignition. Thats a hack at best.

KansasCityREPU

iTrader: (9)

Have you checked the trans fluid?

Tacol0ver

That was done by the mechanic already, both tank and lines where cleaned, and the pump and filter changed. I will go ahead and look into the carburator tho. And the reason I use mph is because in neutral the engine has no problem going all the way to redline. The issue only comes while driving.

Tacol0ver

I agree about the box. I have no idea why they went with that, I guess ignition switches are pricy lol now I just need to find how it was placed and fix it eventually

Tacol0ver

I haven't actually, but will be looking into it for sure. Even if it doesn't fix it knowing the state of the oil might be a good idea

Maxwedge

iTrader: (1)

I forgot if/that you got the tank cleaned. But even so, the idles fine but stutters at speed thing is still classic "bad fuel lines" stuff. Half the new members here start with a "car idles fine but stalls a mile up the road" story. Then they start getting ready for a full rebuild, new wiring, etc., but it's usually just a crusty old fuel system. All of these low-mile examples we find are low-mile because they spent the last 30 years under a tarp. Slowly rotting.

Tacol0ver

Yeah you are right. That was the first thing I did to it because of how common it is for it to happen. Thanks for the input tho, hopefully I can get a driving car soon!

LongDuck

Stock and original Catalytic Converter(s)? These have been known to collapse internally resulting in a blockage that prevents the exhaust from getting out of he engine efficiently. When that occurs, it will rev like he'll in your driveway, but once on the road and under load, it will bog down and not get out of it's own way. One test is to loosen the exhaust manifold where it attaches to the pre-Catalysts, and then take it for a quick drive. Note that it will be louder than opening the gates of hell and you don't want to drive it this way for long due to heat concerns from the now uncorked exhaust gases.

Doing this basically gives the exhaust a place to go other than through the catalytic converter, and will reveal whether the exhaust is the issue at hand.