TR fuel system problems

I'm trying to balance the air/fuel on my TR, using an Edelbrock O2 sensor & LED meter. Even with the factory O2 sensors unplugged the air/fuel ratio keeps swinging back and forth. I would think that since the computer has no inputs from the O2s that it would go to "limp home" or some predetermined point and stay there. But it seems like it's making adjustments anyway. I've thought about disconnecting the fuel system ECUs from the fuel distributors, but am not sure what will happen. I'm sure many will cringe at my primative attempts to adjust my TR this way. But I had it running perfect a while back, but made the mistake of listening to a buddy and tried to tweak one more time and screwed it up. I've been kicking myself ever since. Also cold starting has been a problem, the car would run poorly for a couple of minutes and then smooth out. I would guess the thermo-time switch is the culprit. Do the cold start injectors spray fuel based purely on the elecrical signal, or is the amount of fuel sprayed also affected by the air/fuel settings on the fuel distrbutors? If the fuel dist.s are on the lean side, do the cold start injectors also deliver less fuel? Thanks for listening to my early morning ramblings.

Where is the Eldebrock measuring the CO? With the car sensors unplugged, there would be a steady reading. The ECU has to be connected. The cold start is independent of mixture setting, only injects on cold crank, controlled by temp sensor.
The fuel is very sensitive, sounds like a poor setting giving a poor idle until warm up.

Hi Brian. The Edelbrock unit is simply an O2 sensor hooked to an LED readout, and indicates air/fuel ratios from 12:1 to about 16:1. So I remove the factory O2 sensors and screw in the Edelbrock unit. Thanks for the info. on the cold start injectors. With the fuel ECU O2 sensors unplugged, what would the typical air/fuel ratio be? Would it go to a rich or lean condition (limp home)? I think it would be lean, don't remember where I heard it though. Also, does having the air filter on versus off make a difference? I would imagine that if the fuel ratio is floating back and forth with the factory O2 sensors unplugged it would indicate maybe a vacuum leak? Lastly if the thermo-time switch, if it's bad, is unplugged, would the cold start injectors work until the switch was reconnected? Aren't I just full of questions? Thank You for your patience.

Hi Jeff,

And to think I was havig a bit of trouble diagnosing a lean mis-fire on my "high-tech" carbed BB...

As to the cold start circuit...

Here's how the cold start valves/thermo time switch works:


The thermo-time switch has a metal contact arm inside which is wrapped with a heating element. When it's cold, the arm contacts a ground connection. When you turn the key to start (the cold start valve ALWAYS receives power when the key is in start, and ONLY when the key is in the start position -- temperature is irrelevant as far as the cold start valve itself is concerned) 12v is sent to the cold start valve. If the thermo-time switch is cold, then the thermo-time switch grounds the cold start valve, allowing it to inject fuel. When the key is "on" the heating element in the thermo-time switch is warming up and slowly bending the contact arm, and so once it gets warm enough, it breaks contact and no longer grounds the cold start valve, shutting it off.

However, this applies only when cranking. The cold start valve never receives 12v when the engine is running, i.e. when the key is in the "on" position, only when the key is in the "start" position. So, to answer your question, no, the cold start valve is probably not staying on, unless you've got some weird wiring.

And the thermo-time switch does not supply 12v to the cold start valve, it merely supplies a ground for the cold start valves.

Regards,
David

Hmmm...very interesting David...Thanks. My TR has the KE Jetronic system. I don't think there is a cold start VALVE, but it has the electric injectors on the side of the intake plenums. But using your information, the cold start injectors work only during cold cranking. If cranking when warm (thermo-switch warm) then they will not operate. I can understand this. But what about just after start-up, when the engine is still cold but running (not cranking)? Where does the cold running enrichment fuel come from? I thought that the KE Jetronic cold start injectors continued to work until the thermo-switch reached a certain temp. and then shut them off. I guess I'd better do some more reading up on this issue before displaying my ignorance for all to see. Thank You for your help Brian and David.

The cold start injector is on the plenum. You should have one on each side. It will have a blue harness connector on it.

Yes Richelson...they are located on outboard center portion of the intake plenums. What I need to know is: What operating conditions do they work in? I know they spray at cold cranking, but I believe they also are energized during cold running while the engine is warming up, and stop spraying when the thermo-switch reaches it's grounding temp. At least I think so at this point....

Jeff,
You're understanding of the cold start function is correct...Typically, the maximum time the CS injectors will fire is about 20 secs. The signal to initially fire comes from the starter circuit...then if coolant temp is below xF, we get a cold start injector spray...else, the starter signal is ignored.

Presuming a totally cold start, the CS injectors spray until the coolant temp reaches xF, as usually specified on the thermo-time switch.

Regards,
David

Thank You David. If the thermo-time switch is bad, then I assume the cold-start injectors would fire during cranking only, and then stop firing when the ignition key is released to the engine-run position. My car fires up fine, but then runs terribly for a minute (or less) and then the idle smooths out. So I would guess the switch is bad. I'll pull it and test it per the shop manual procedure. I will also check the auxiliary air valves too. I'm getting my car close to running properly again. If my backyard mechanic methods work, I'll be one happy guy. I know I can get it right, just gotta be patient. When it was spot-on before, the car ran like a banshee. It did everything so smoothly, rev'd great and dropped back to a perfect idle every time. The car even seemed to shift and drive better. I'm amazed that the fuel mixture adjustment screw is sooooo sensitive...it doesn't take much movement to have a big effect. It's almost too touchy. I still wish I knew what the air/fuel ratio would be on a perfect running car with the O2 sensors unhooked. I could tune to this value, hook up the O2's...and theoretically be close to optimum. And I still would like to know why my air/fuel ratio swings back and forth when there are supposedly no controls working. In addition to the O2's being unhooked, I wonder if I should disconnect the ECU inputs to the fuel distributors so there is no chance of adjustments? Just rambling here. Thank You Everyone for your help and input.

Jeff,

As someone suggested, the A/F ratio swings are probably due to some intake leak. However, if this was true, then you should hear the engine revs change with each swing........I would think.

If not, then, my conclusion would be a "slow" Edel.. sensor unit. The only other thing, I could think of, is a fluctuating response by the "pressure actuator" located on the FD body.

Just my thoughts!!!!

BTW: Are the A/F ratio swings noted on both banks?

(Message edited by henryk on October 05, 2004)