richard21a

hello,
I have a 1988 mazda rx7 and the fuel sending unit was bad, so I put a universal one in,sunpro and changed the spark plugs because the car has sat for 4 years or so. After I installed the parts,the car will turn over and fire and run for about 10 seconds. When it goes idle the car compleatly bogs out. My basic understanding of the situation is that the fuel system is priming and allowing the car to start, but one the key goes into the run position the fuel pump stops running. Is this a fuel issue or a wireing problem, or a airflow situation. And this is my first rx7 I have ever worked on so open to any suggestions.

thanks,
Richard

RotaryRocket88

iTrader: (7)

Did the car run prior to changing the plugs and the level sender? If the car sat for a long time, you should probably replace the fuel filter, fuel hoses, and possibly vacuum lines too. Was the gas in the tank treated with any stabilizer, or has it sat turning to sludge over 4 years? There are some related tips here: http://www.aaroncake.net/rx-7/unstore.htm.

richard21a

Well upon reading that post you put on my thread, I can say that the car was improperly stored haha, but the car was really maintained. I knew the owner and what he did to get the car started before he sat it. starter fluid in the intake was the key, but now that i have ahold of it, im fixing the problems now. sending unit diod was bad wasnt making a connection so thats why i replaced it. yes the car did run before it sat and really well. but taking into consideration of the fuel system components it might not be a bad idea to check the fuel filter and drain the tank, i did mix old gas with new, and put hi octane in it, along with injector cleaner and system restore gum out. but like i said i cant get the car to stay running long enough for the gas to go through the system. but their is something i cant figure out about the negative charge system. the system is priming but the fuel pump isnt constant. what i have read is that the fuel pump only runs as the car is cracking over then stops, or is the sensor on the sending unit supposed to tell the pump to keep running after the system is primed and the key is in the on position? and i removed the plugs and wires first and the plugs were wet and fouled, so i cleaned them to the best i could and reinstalled them, but same outcome, I put new ones and the car is at the point of fireing on command now. so that fixed some what of the problem but not all of it. so now im at a loss !!!!

RotaryRocket88

iTrader: (7)

The fuel level sender has zip to do with fuel delivery. It's just there to send a signal to the fuel gauge. (You are talking about the level sender, right? The black box on an arm?)

The fuel pump runs under a few conditions:
1) The key is to 'START'
or
2) The engine has started running, and the AFM door is pulled open by engine vacuum. This disables the AFM's internal fuel cut switch.
or
3) The fuel pump test connector has been jumped (yellow 2-wire plug by passenger shock-tower), and the key is to 'ON'.

If a bunch of crud was sucked in when you first started the car, the filter sock on the fuel pump could be plugged, the fuel filter could be plugged, or the injectors may be sticking open. The last one would explain why the plugs came out wet with gas & fouled.

Another option is the fuel cut switch in the AFM is not working correctly, and is cutting fuel once condition #1 is gone. Jumping the test connector would bypass this. You can also test the switch with a multimeter. The FSM will tell you which pin on the AFM is for the fuel cut switch, and the resistance value should either be 0 or infinity depending on door position.

richard21a

alright man i appreciate the help, but after today of nothing but troubleshooting I finally found the problem. The maf. sensor is acting up. The flap was sealed shut and needed excesive force to open it, so which tells me that the flap wont open with air intake air flow. And the sensor was also bad cause i got 0 reading across the board when i finally got the flap open. But i am going to take your advise and go ahead and replace all the fuel system components all together, might try to have the injectors cleaned cause the cheapest i found so far were 379.00 a peice. So i might make that my last fuels system maitnence check. unless you no where i can find them cheaper?

RotaryRocket88

iTrader: (7)

What you're calling the MAF is the AFM (air flow meter) I mentioned. If the door was stuck shut, the fuel cut switch was being enabled as I suspected. Once the engine starts and the key returns to 'ON', the door must move to keep the fuel pump running. It's a safety feature to prevent the car from burning to the ground after a crash.

For the injectors, just have them cleaned/serviced. I've used these guys before, and you can't complain about $19 an injector: http://www.witchhunter.com/.

richard21a

yeah your right afm was the issue, ill check out those guys out for the injector cleaning as well anything else i can to do the car to get is running to its peak performance? you seem to have a lot of useful info so im taking your word on these things. haha

RotaryRocket88

iTrader: (7)

Depending on the condition of the coolant/heater hoses, you may want to replace them as well. The formed lines are not exactly cheap through Mazda, but neither is replacing an engine if an old one bursts. I replaced all of these when I first bought my car, along with every vacuum hose.