A bit of background on the car first: It is an 1986 5-Speed GXL. 130,000 miles on it, bone stock, except that I removed the pulsation dampner about 10,000 miles ago and replaced it with a banjo bolt. The engine probably has around 40,000 miles on it now. The car ran great and got 20MPG city, 24MPG highway. It did have a strange problem that started to develop that the power would surge slightly, especially noticable at 2KRPM and then again at 2.5KRPM. It got worse as I drove the car, but it was never very pronounced, just noticable.

-- So, on to the problem:

I was about ten miles into my daily commute to work, cruising along at 2100RPM in third gear, (car is running fine) and all of a sudden, out of the blue, the tach dropped to zero, and I lost all power (combustion stopped). Now, the engine was still spinning, as I was still in gear. The tach just said zero (A CLUE!). I couldnt get the car to kick over or anything while I was in gear, so I pulled into the shoulder and tried the starter. It wouldnt start, it would roar to life and then die instantly. If I held the starter on and feathered the gas, sometimes I could get it to go to 2000RPM, but it would die as soon as I let off the starter. After it sat for a few hours (on the side of Interstate 495) eventually I could get it to start and run like crap for a minute before it would die again.

Ok, so, eventually Pele (an RX7club member) came and towed the car for me. Now I've got it where I can work on it. I started with the ignition first, because of the tach dropping to zero.

I replaced the leading coil/ignitor unit with a known good unit (I know trailing is where the tach signal comes from), and replaced the plugs, and tested the wires. Still had the same problem.

I checked fuel pressure while I was at it, and it is perfect.

I checked the leading ignition with a timing light and it was doing some crazy stuff (like firing at the complete wrong times, or for short periods of time, not firing at all.)

SO, I replaced the whole ECU with a known good unit. STILL does exactly the same.

Think the CAS could be bad? Any ideas what I should check next?

Thanks in Advance and all help is appreciated.

- Jason

 

Also, trying to rev the engine now works somewhat OK, when I rev up to 3.5KRPM or 4KRPM the engine will suddenly cut out and die (cannot be saved by feathering the throttle) (The revving is done in nutral)

I have tons of parts and parts cars so swapping parts around isnt an issue if I can just find out what part is bad.

 

Can you do an ECU error code scan?


-Ted

 

Yeh, I'm going to give that a try when I get off work today. I don't have the internet at the house, so I have to print out the information on shorting that diagnostic pin here at work.

 

look in the intake piping maybe on the left side the hoes couldve fallen off happened to me once and the car started and died

 

If you add a capful of ATF in both rotors through the sparkplug hole and it help the car start run better, it could be low compression.

 

check that your throttle position sensor is working properly. My car acted the same way and I couldn't figure it out until I unplugged the connector and saw all the green corroded ***** in there. After cleaning it up, the problem disappeared completely.

 

its the airflow meter. swap it out and see what happens. i dont know why this happened to me, but the same exact crap happened to me. it would never start again. untill i threw it out it started again. try and replace it.

 

Yeah, i had a 87 that did that same thing. I would say the airflow meter also.

 

OK! I tested the car and it's not throwing any codes at all. And just to test it to make sure that the ECU wasnt just not telling me the codes, I unplugged the TPS and it threw its code. Same with the MAP.

The car has very good compression.

So, it's not the TPS, though the TPS might be a little old. The only things I have left to guess is the AFM and the CAS. I will swap out the AFM first tho.

Thank you all for your suggestions and advice.

 

The RPMs dropping to zero tells you it's almost for sure the CAS man... check that out first.

--Gary

 

noooo, poor rocky ( tofu's rx7's name ), hope he gets better!

 

Aren't you the guy running megasquirt 'n spark on his NA, Tofuball? You must have two FC's. I'd say pull the stock computer and megasquirt it - problem solved, hahaha.

(sorry I don't have anything useful to contribute to the thread.)

 

if rpm drop to zero and motor is still spinning its somthing ignition related. maybe the ignition wire by the battery is corroded or somthing? or the CAS might be going out,


ive had where i hit a bump and my ignition would cut out, and that was cause of corosion on the main ignition power wire .

 

either your maf fell of or got disconnected. I had the same problem when I upgraded my turbo. The surge would shut the flap and push the afm out. But check out the maf.

 

Are you getting spark till it cuts out? Have someone pull the spark wires off the coils a little bit to see if it sparks while cranking and when it first cuts out. If i remember correctly when my AFM came disconnected while cruising the TACH was slowly dropping as the car was slowing down. But that was a long time ago. And my memory is horrible

If your getting spark then the ignition is fine. The TACH gets the signal from the trailing coil. The engine will run without the trailing so anything getting a tach signal isnt required for the engine to run. The engine runs. So you are getting spark and the tach works while its running. Try cleaning all the connections. Make sure nothing it corroded.

You have fuel pressure. And the engine will start. So you are getting fuel

If you AFM was the calprit. Your engine would start every time but would only rev to about 3000 rpm If you have the cold start still enabled. Otherwise it may start or may not.

Your TPS is not the problem. The TPS cant cause this problem. Maybe on a S5. but not on a S4

Cant think of much else.

 

even though you said you checked the fuel pressure i had the same problem when i installed my walbro, go find the little yellow plug near the afm some where and put a jumper wire across it. put the car in the on position and you should here your fuel pump going. turn it on and see if it stays on. if it does then it means you need more voltage back their.

 

I doubt it's the CAS.
If the CAS was bad, the ECU would've triggered a code for it.

If the ECU lost power, it would kill the tach.
If the (trailing) coils lost power, it would kill the tach.
If the instrument cluster lost power (i.e. blows a fuse), it would kill the tach.

Did you check the 3-second initial self-test for the ECU?
When you initialize the error code scan, it should light up the CHECK ENGINE light for 3 seconds...


-Ted

 

Yes, my Convertable is Megasquirted.
This is my GXL :p
I have many, many FCs :p

Hrm. I'll just pop a multimiter on it. Thanks for the suggestion

Yes, it did the 3 second initilization. HOWEVER!!!! I have no check engine light! (It is a 1986)

I have no idea why the ECU is not triggering a code.

What would you suggest looking at?

 

(Right now I am praying that it is the AFM, as that is simple and easy to fix )

 

Ah, okay, so you used a pair of test lamps at the check connector?

Okay, if nothing major is triggering a code, it comes down to either spark or fuel.

Spark is pretty easy to eliminate, so I tend to diagnose that first.
Can you confirm you have spark?
Pull spark plugs wire boots and place them near a ground - look / listen for spark arc.

If that passes, then it comes down to fuel.
Usually it's fuel pump, fuel filter(s), or fuel injectors not firing correctly (i.e. no power to fuel injectors or fuel injectors are clogged).


-Ted

 

Well, it is not the CAS or the AFM either. Swapped those out with known good units and the car still preforms the same, and still does not toss any codes.

OK, I have used a timing light to show that I have spark, and I did your method (pulling the wire) and it shows I have spark. However, the timing light shows that spark is intermittent while the car is 'running' (when I feather the gas to get it to start and hold it at a few thousand RPM).

I CAN get the car to 'start' by cranking it without pressing on the pedal, it sounds like rrrrrrrrrr*ROOOM(tach at 1K, then dies)*rrrrrrrROOOOOMrrrrrrrrrrrrrrrROOOMrrrrrrrr(e tc).

 

Try jumping the fuel pump connector under the hood?
Sometimes the fuel pump cut-out switch in the AFM goes bad, and it prevents the fuel pump from working correctly.

It *sounds* like it's starting fine, but it doesn't stay running?


-Ted

 

OK, I guess the pinout is in the FSM? I'll look it up on monday I guess. Thanks for the suggestion

 

UPDATE:

Allright, Ken (MuyThaiBxr) came over and we started testing the sensor leads at the ECU one by one. Apparently the coolant tempreture sensor was reading something like -80 degrees centegrade. We take a look and the wires going to the sensor are all screwed up.

I'm going to give that a shot tommorow night and see how things turn out.