kc92hatch

Hello all,

I could use some help - I'm having a hell of a time fighting an intermittent no start problem.

1997, running generally pretty well. There is a slight miss/vibration throughout the rev range, but I haven't tracked it down yet...maybe transmission mount? We'll see.

Car seems to always start with the engne cold. But after a drive that fully warms up the engine, I'll park and let the car sit for maybe 20 minutes (+/-) and I might (not always) then get a no start. Engine spins, but it doesn't start. I've tested for spark and no spark in this situation.

When this happens, after a couple attempts, the CEL will come on with code P0335 (crankshaft position sensor circuit trouble). Car, after sitting some time maybe an hour or two, will eventually restart. I haven't had this happen with the engine running. I tested the impedance of the sensor and it is 1400 ohms. Seems to be about this value both hot and cool.

The test of the sensor seems like it is OK, but this seems like certainly something going on with the crankshaft position sensor circuit and seems to be temperature related. I hate to throw a new sensor on it when the old one seems fine, but I'm about out of ideas.

Open to any suggestions!!!!

Thanks

Yamae

I would check the waveform generated by the CPS when cold and hot first using an oscilloscope or a scanner which can read the waveform. The resistance 1400 ohms is only one side of the characters. The CPS changes the character depending on the temperature. It is often the case that the amplitude goes too small when hot among aged CPSs.

kc92hatch

Thank you Yamae. You are a steely eyed missle man! (A compliment!) Based on your input, I think I'll try a new sensor. I'll post back results.

dicer

Since the symptoms and code says cps I would have just replaced it.

sha4000

iTrader: (1)

I agree even though it checked out ok.

kc92hatch

Well *&^%!!! New crank position sensor did not help. Same problem. Here is a run down of the situation:

1. Have been battling slightly rough running and misc. trouble codes.
2. Recently replaced ECU capicators. None were leaking, but the ECU was original. Hard to tell how much improvement. No weird codes any more. The problem described below also occurred before the capacitor replacement.
3. Recently replaced spark plugs.
4. When the engine will start / stay running, it is running quite good. Firm transmission shifts, good power through the RPM band. Have done multiple full throttle 6K RPM shifts up to about 100 mph....car seems strong and happy.
5. Car has not stalled out on me while it's been running and under way.
6. When car is cold, seems to start fine, no issues.
7. After a bit of a heat soak after running, car either doesn't start (no spark either) or,
a. I've started it, then turned off. Started again, then turned off, and if I keep this sequence up for three or four times, eventually, the car will start and then within about 5 seconds it will quickly die. Once it dies, then on subsequent restarts it will either not start at all, or maybe try to start for 1 or 2 seconds and then die.
8. Yesterday, after what I describe in 7a, I would get code P0335 (Crank Position Sensor circuit malfunction). Today, I'm not getting any codes at all.

Yikes, I don't have a clue what's going on here..............ECT sensor? Maybe something bad in the ECU unrelated to the capacitor problem?

Another thing to mention. I have read on this board folks disconnecting their MAF meter to troubleshoot the meter. They say if you unplug the MAF and the engine runs better...... In my case, if I unplug the MAF meter electrical connector while the engine is running, the car dies immediately. Also, with the meter unplugged, I can also not start the car. Just throwing this out there in case it might be relevant.

Any help or suggestions are appreciated guys!!!!

kc92hatch

Updated the last post to add a section that the car won't run / won't start with MAF unplugged....just in case that might have bearing on the situation.

Could ECT sensor be part of problem? Maybe something wrong in ECU unrelated to the capicators?

Hmmmmmmmmmmmm...........

Yamae

So it was your fault.
Remember that when the ECU detects one of following conditions, it forces the circuit opening relay open not to supply +B to the fuel pump. Thus the engine has no idea to keep running without the gas.

1, No signal from the MAF for more than 3 seconds.
2, No signal from the crank position sensor for more than 5 seconds.
3, No signal from the cam position sensor for more than 5 seconds.
4, No IGF signal from the igniter for more than 3 seconds although the IGT signal is sent.

Why don't you measure the resistance of the ECT sensor. It shows 2 kohms or more when the engine is cold, once it reaches to the operating temperature, it shows less than 400 ohms. The ratio is more than 5 times and you can judge it good or not very easily.

kc92hatch

OK guys, we're getting close. More trouble shooting with these results.............

A. ECT sensor: 2000 ohms when cold, 320 ohms when engine at operating temp. So looks OK.
B. Did some more testing......after the engine is at temp and I turn it off, but I LEAVE THE HOOD/BONNET up, the problem will not occur. If I do the same test, get engine at temp, turn it off and leave the hood/bonnet down, problem will reoccur within about 15 minutes.
C. This is very repeatable.

So seems that something under the hood is getting too hot after engine shutdown and hood down. The likely reason this doesn't happen happen while driving is that there is plenty of air circulation under the hood, so things stay cool enough.

Still no engine codes. If you recall, when this problem was occuring before, I was getting a crankshaft position sensor circuit malfunction (335) code. I replaced the sensor and that did not fix the problem, but code 335 has not returned.

Could the ignitors be faulting under higher temperatures? If not the ignitors, what other electrical/electronic devices under the hood could be suseptable to heat?

Also, if it could be the ignitors faulting under high temperature, could that also be the reason why I'm having a slight engine miss throughout the RPM range?

Thanks for your thoughts, I think I'm almost to the end of this problem.

Yamae

I'd check the igniter to let it arc in the air not in the cylinder. The spark should travel more than a half inch/12.7mm at under 1 atm/ambient although it travels only 1/10th in the cylinder at 10 atm or more.
Instead of a spark plug, you need to prepare and use an air gap of 1/2 inch. Try this when cold and hot.

Correction: Regarding the resistance of the ECT sensor, it should be 322±32 ohms at 80 degrees C. So your ECT is just good.

dicer

If you had someone with a good scan tool all the tests could be done to find the fault. If its like gen 1 there are 2 cam sensors that play into the equation also. I have had igniter or also knows as pulse amplifier on other cars be the cause of temperature related running and start problems. Need to look for the signals from the position sensors too.

kc92hatch

Hi guys,

Checked both igniters today. When the engine was in a no-start / no-spark condition (due to car being run in idle to operating temperature, with hood closed, then turned off and about 20 minute wait), I ran the igniter bypass test and both fired.

So that seems to tell me that the igniters would correctly respond to a command from the ECU.

So items that may still be problems:

1. Cam position sensors. No codes, but I'll check their resistance hot / cold.
2. Igniter feedback to the ECU. If I understand correctly, the igniters feed back "firing" to the ECU for confirmation. I confirmed that igniter fires, but not that feed back was sent.

Beyond these two items, I'm at a loss. Again, this is a condition only present after engine heat soak.

Thanks for any suggestions!

kc92hatch

I'll be checking the cam position sensors as soon as I can.

In the meantime, I was thinking about other under hood components that could be affected by heat. Are there any relays that if not operating correclty, could cause the ECU to not fire the ignitors?

The one thing I know is that when this issue happens, it results in no spark. So what components under the hood could be heating up (are suseptable to heat due to age, etc.) and are part of the ECU igniter firing circuit?

Thanks for ideas!

dicer

Go to the Toyota site and look at the manual, or to a dealer. Study the trouble shooting charts, it should give a step by step elimination process. Do both coils not fire when this heat issue happens? If its both its not ignitors or coils, both aren't pooping out at the same time. The only other things could be position sensors. Relay ? don't know.

kc92hatch

Thanks Dicer, good advice.

Yes, both ignitors are dead in the "overheat" condition. No spark on either cylinder bank.

I'll post back as soon as I come up with anything else. In the meantime, if something comes to might that would be worth a check, jot it down!

Thanks all!!!