EJnMN

Have a strange starting condition that I need help diagnosing. Thought I had it fixed, but it came back.

Car is an 83 NA, daily driver, but slowly evolving to track car. The emissions works are gone. Air Oil Separator runs to catch can. AC is deleted. New starter, New Battery, Newish plug wires, DME/Relays, etc last year. other irrelevant mods.

After the emissions stuff was deleted, it would require a little bit throttle to keep it running until it warmed up. No biggee... by the end of the block it would be running perfectly.

A few weeks ago, it started to behave oddly when I hit the starter. It would rev up to a 2k or so, just like when it normally started, as if it was getting a little fuel, for about half a second, and then when revs start to fall, they'd just fall all the way down to zero, when I hit the throttle it did nothing. I would turn it over like this many times... maybe 5 to 10 times if it had been run in the last hour or two, maybe 20 or 30 if it sat all day while I was at work. Eventually, it WOULD start... and run great. No problems at all once it started. After it warmed up, like if I went and ran an errand and came back out, it would start right up just like new.

We diagnosed it as a Throttle Position Switch... confirmed with Clarks Garage test of the switch. I replaced the TPS and it started fine. When I set the old TPS on the work cart, it was completely full of Oil. (I've been fixing oil issues for a while... recently having redone the balance shaft seal)

I ran it for a week or so, it ran fine. Then the exact same symptoms came back. I have not yet pulled the TPS to see if it magically filled with oil again. (Note, with emissions stuff gone, there should be no way for oil to get back up there anymore)

Has anyone out there seen anything like this? As I mentioned, once I get it started, it runs fine. It's like something has to be woken up, or dried out, or freed up... and then just fall back after it sits.

F18Rep

Common on turbos but not NAs. Suggest you peek in through the TB an see if oil is present in the intake. Or, maybe an over-serviced K&N filter. ;] Bruce

EJnMN

I agree that's what it seems like. (I should have some free time to pull it apart tonight) But how would the oil get into the throttle body now? The AOS goes to a catch can, not the intake. The two other connections in the J boot and underneath are capped. The only connection between the Intake and anything besides the fender wall is the vacuum line to the regulators on the fuel rail. (and the big line from the brake accumulator to the intake manifold, but that is after the TB)

EJnMN

I checked the inside of the throttle body and its dry as a bone. Just as it was after I cleaned it.

New data... there seems to be a correlation between temperature and the number of cranks it takes of it to kick in and start. On a cold, damp day... 20 or more. Today, hot and sunny... about 5.

EJnMN

Also...a bit of fuel smell when it starts

Black51

I'd take a peek at the temp sensor. I've heard others guys here issues like this before due to the temp sensor. Especially since you've shed light on the temp related starting. Pretty sure that if the temp sensor's not working, it gives the dme a false temperature reading, and thus the car won't stay on when cold.

Someone correct me if I'm wrong, but I think our cars' dme's have a setting for cold starts and hot starts. For cold starts, the temp sensor gives the dme a temperature, and the dme interprets the engine is doing a "cold start", so the dme sends a little(actually a lot) extra fuel to keep the car running. For "hot starts", well the engine's at normal or close to normal op' temp. So not as much extra fuel needed... But it seems like your temp sensor isn't giving accurate info to the dme for starting, more so for cold starts.

So to sum it up, check the temp sensor. Hope this helps.

EJnMN

Nice Call!!


Disconnected the temperature sensor above the balance shaft and it started right up. After a couple seconds it started running rough with it disconnected. (There was also fairly significant cloud of smoke, which wafted leisurely into the open windows of my neighbors at 7:00am ... so I suspect I'll hear about that.) I then hooked it back up, and it started fine that way, the engine having been warmed.

Looks like I'm shipping days away from being back on the road.

Thanks!!

Black51

Glad to hear you found the problem!

EJnMN

Well.... I thought we'd found the problem.

I got the new DME Temp sensor in the mail last night. Put it in and fired it up. Started perfectly the first time. Tried a couple times. Ran fine. Went to bed with a smile on my face.

Got up to go to work this morning... no joy. Exact same problem as before.

Didn't have time to do any diagnosis. Not sure what I'd check at this point.

EJnMN

So last night... when I went home to diagnose the problem. It started right up. Drove it to dinner, back. No problems.

This morning, it did eventually start, after 10-12 attempts. Same old symptoms. Smelled very gassy when it did start. I don't think that the other temperature sensor goes to the DME... that one is just for the gauge, right?

EJnMN

Soo... I've been driving the car for the last few days... basically I learned the right way to get it to start and it's pretty reliable. I thought I'd post what I do, and see if anyone had some ideas what might be creating the situation.

Basically, when I start the car, I turn the key over to get it to start, and then after it has revved up, on the way down in RPMs, I put just enough throttle to throw the TPS switch, but not enough to give it any large amount of fuel. If it stumbles, I click the throttle right on the edge of closed and releasing the switch until it starts to run, and then I give it enough gas to get it up to about 2k rpms for a second or two until it is steady there, and then I just hold it around 1k until I've driven a couple hundred yards. After that, all is fine.

peanut

have you tried to replace the DME relay with a 3x wire bypass ? see how it starts and runs with the bypass in place.
(see Clarkes garage workshop manual for DME)

EJnMN

Interesting. If it happens in the morning, I'll try that. I have a spare DME relay too I could try. (I have a spare DME as well... I suppose I could try that if the relays don't make a difference)

peanut

if you use the bypass wires and the car then runs ok , it will elimininate a lot of the cars components being the cause of the problem and help narrow down the search. Its diagnostic in other words .

Have you tested the thermistor or temperature sensor yet as Black51 suggested ? Your initial fuel mixture is determined by this component

peanut

spot on

on the early cars( ie pre 85.5 ) if the temperature sensor senses the engine is cold the ECU (engine management unit) increases the number of pulses to the injectors thus increasing the amount of fuel delivered for 10 seconds or so.

On late cars there is actually a fifth injector called the cold start injector and that gives extra fuel delivery when the engine is cold as measured by the engine temperature sensor. (not to be confused with the coolant temperature sensor.