Rx7_Nut13B

iTrader: (1)

Hey there everyone, It has been a long time sense I had to ask for help with a problem, but this one has me stumped.

Specs First..
Fresh rebuild with street port (About 15miles so far)
Stock S5 ECU, Injectors (Cleaned) and Mass Air Flow Meter
Compression Cold (Front Average 91) (Rear Average 88)
Compression Hot (Front Average 103) (Rear Average 99)
Vacuum 17-20in/hg @700-900 rpms
Idle Rock steady

The problem is it is very hard to get started when it is cold, but if I shot just a little starter fluid into the intake it will fire right off and hold a steady idle. This would lead me to believe that it is a fuel issue, but the rock steady idle and drivability of the car would push you away from a fuel problem. The timing is pretty close, I hate how the TPS will change the ignition timing and there isn’t a way to lock it to a set point, I have tried it advanced (didn’t like that) and retarded (little better). The real problem is this engine has a aftermarket main pulley and has 4 timing marks instead of two so I cant really tell witch one it is suppost to be on, it looks like a Mazdatrix pulley I think. The thing isn’t even trying to hit off when it is cold, like there isn’t any fuel, very little in the combustion chambers, or the timing is just to far off. But the idle is what is pissing me off, it is great.

After the car is warmed up to operating temp it will fire up(1-3sec of cranking) again this pushes you away from fuel problems.

Then I was thinking it could be a sensor giving the ecu some bad data but most of the time on S5's they will throw a check engine light. While this is only sometimes true, this car isn’t saying anything is bad, but this doesn’t mean a sensor is out thou.

The only thing that I am going to try and fix is the slow starting, this could be causing the problems but it doesn’t affect the hot starting. I don’t have a exact number for cranking rpms but it isn’t the fastest I have seen. The only thing that worries me about the starting is the car has a TII Drive train with a NA motor, I don’t recall the gear reduction of the TurboII (lower compression) vs. the NA (Higher Compression) this could be the cause of the slower starting speed. When I say slow I am not saying barley moving, it should be turning fast enough to start even when cold.

That is about it, I have been fighting this problem for 2 or 3 days and just can’t track down anything that would cause it only when it is cold.


Here is a video that I made showing how it is running and driving, when the car is idling at the very first of the video I had the idle a little high, sense then it has been dropped to a more stock location. Then it shows the vacuum at idle, then a hot start and idle, then just a little bit of driving around. Remember this engine has only a few miles on it that is why I am keeping the revs low at this time.

http://s19.photobucket.com/albums/b1...eenRebuild.flv

Thanks for the help in advance, like I said it is weird for me to ask a question like this, but i am out of ideas.

Rx7_Nut13B

iTrader: (1)

Small Update sence I typed the above.

I have learn about something I never new, that the stock Ecu has a start fuel map, and that it doesnt look at the mass airflow sensor on startup.

The reason I bring this up is because, the wiring in this car has seen some mods, i noticed that the starter control wire ( single wire to starter to activate it) isnt connected and there is another wire ran to the starter. It could be that the ECU isnt seeing a start signal and is defaulting to the mass airflow sensor witch would not give enough fuel to start it when cold but would when hot (Colder engine needs more fuel then when hot). I am going to look at the wiring when i get to the house and see if the ecu is seeing this start signal.

Please feel free to add anything else.

HAILERS

Yes. That and make sure the water thermo sensor circuit is not open. As in the plug is connected up on the sensor on the back of the water pump housing. And or check the voltage at the sensors wire at the ECU with all plugs connected up.

arghx

iTrader: (3)

I would completely replace the water thermo sensor (like $35 from the dealer maybe) and verify that the wiring is good. Even when the wiring is good they can read inaccurately. I know there is an FSM diagnostic procedure but you should replace it anyway.

scrip7

iTrader: (6)

Having a rock-steady idle tends to rule out vacuum leaks. Having to add external fuel such as starting fluid indicates not enough startup fuel enrichment. Check that starter signal like you said. As was mentioned, the coolant temp sensor can be the culprit, and it doesn't always trigger a ECU code/ check engine light. The sensor resistance can "skew" out of range after 15 to 20 years of use and thermal cycling. An open or shorted sensor will give you more severe symptoms, but a skewed sensor may not. You could take the time to use a DVOM and compare resistance readings with actual coolant temp via the chart in the FSM, or just replace the sensor. Removing the alternator makes it easier to change the sensor. Also check voltage at the fuel pump connector under the rear carpet while cranking. I have seen quite a few bad pump resistor/relays (my GXL had 4 volts at the pump about a year ago due to a bad resistor). Engine compression numbers should also come up once the engine is broken in, depending on the rotor housings that were used in the rebuild.

HAILERS

You don't have to ohm out the sensor. You just backprobe the sensor and watch the voltage drop down to approx .5vdc when the engine is fully HOT. Fully HOT is when the stock thermostat is approx 180*F.

You backprobe while the engine is idling and watch it as it drops.

A disconnected senor circuit will be close to 5vdc whether the engine is hot or cold.

A cold engine will start off with a voltage of b/t 2-3vdc and steadily drop to the half volt once fully HOT.The upper voltage depends on how cold the water is. In Summer after sitting overnigt it'll be in the 1-2vdc range. Colder will equat anything over that.

If you had a RTEK2.0 you could simply watch the water temp on it drop down or default to a open sensor.

You say you have no faults so it seems you took the right path to see if there is a START signal from the start circuit. Lack of a start signal means the Lean afm will be used and the internal start map won't be used.

1C should see 9-12vdc anytime the key is put to Start.

HAILERS

Not that it matters since his problem is lack of a start signal, but I went out to one of the car that's been sitting since yesterday and metered the water thermosensor.

The water is 42*F and voltage reads 3.09vdc. Then started the engine and let it idle. 50.7*+2.6vdc..........60*=2.54..............70*=2. 25.............80*F=2.02vdc.....................90 *=1.76vdc..........100*F= 1.57vdc.........120*=1.15vdc....................13 0*=1.00vdc..........140*=.89vdc..............150*= .78..............160*=.69...........170*=.56vdc... ........176=.53vdc. Couldn't get to 180* It's a little problem with who I bought the thermostat from.

Not the thread owners problem though. Just FYI thing.

Rx7_Nut13B

iTrader: (1)

Well a big thanks to everyone that posted

I have learned something new, that is hard for me, thought I new just about everything about FB's, FC's and FD's and still working on Cosmos.

The Startup map was the problem, the car wasn't getting the Start signal to the ECU. Made a jumper wire to it and fixed everything, Cold Start up, hell any start up.

I just goes to show you that you have never learned everything.

HAILERS

I've often wondered about the threads that say they have installed a switch and *new* power wire to turn the starter over. Might work in hot/warm climates, but it seems to me it would cause problems in temps under ??? 50*F or less.

Good to hear *old timers* can still learn. humor

scrip7

iTrader: (6)

Good info Hailers. You might want to keep these numbers handy for other threads. Seems like somewhat of a common topic

To the OP, glad you got her fixed up!