short term engine start problems
10-17-17, 08:04 AM
#1
Lead Lap
Thread Starter
short term engine start problems
First off, this is about my grnadsons 1991 lexus ls400, not my 1996. He called me last night and said his car wouldn't start, so I brought my basic tool box and volt meters with me. I got there and found out it would start fine and then die within seconds of running. I must have tried starting it about 25 times with no success. It also didn't seem to have any throttle response in the short time it was running, the rpm wouldn't go up if you floored it. I did notice that after it died, the engine oil light would come on(like it should on a killed engine) but also the coolant light came on. I checked and sure enough- the coolant in the overflow was very low. You could barely see it at the bottom of the tank. I went home and came back and filled to between the two lines. I tried starting it again, but it died like before. I tried it again, but while it first started, I went to neutral and revved it and for the first time it responded to the accelerator and continued running. After it started, it continued to work normally on all further start attempts. Could a coolant sensor on top of the engine caused this because of low coolant? My son-in-law is leery now of letting his son drive the car and I'm trying to figure out a plausible reason for the fix(?) I did on the car.
Last edited by jaaa; 10-17-17 at 08:08 AM.
10-17-17, 10:35 AM
#2
how many miles are on the car? as with all of us here, we always suspect the ECU to be a big culprit. it is known to have bad capacitors, thus displaying similar issues to what you are experiencing.
https://www.clublexus.com/forums/ls-...capacitor.html
low coolant is of a minor concern bc the engine should still fire up and idle even with low coolant.
https://www.clublexus.com/forums/ls-...capacitor.html
low coolant is of a minor concern bc the engine should still fire up and idle even with low coolant.
10-17-17, 05:02 PM
#3
Lead Lap
Thread Starter
how many miles are on the car? as with all of us here, we always suspect the ECU to be a big culprit. it is known to have bad capacitors, thus displaying similar issues to what you are experiencing.
https://www.clublexus.com/forums/ls-...capacitor.html
low coolant is of a minor concern bc the engine should still fire up and idle even with low coolant.
https://www.clublexus.com/forums/ls-...capacitor.html
low coolant is of a minor concern bc the engine should still fire up and idle even with low coolant.
10-17-17, 05:40 PM
#4
Moderator
What happens when starting fluid is used? Does the engine continue to run as long as the starting fluid is sprayed?
A 91 has two separate injections. One is only for the starting up and the other for the engine running after that.
It seems to me that your problem is related to the above switching.
A 91 has two separate injections. One is only for the starting up and the other for the engine running after that.
It seems to me that your problem is related to the above switching.
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jaaa (10-18-17)
10-18-17, 10:54 AM
#5
Lead Lap
Thread Starter
What happens when starting fluid is used? Does the engine continue to run as long as the starting fluid is sprayed?
A 91 has two separate injections. One is only for the starting up and the other for the engine running after that.
It seems to me that your problem is related to the above switching.
A 91 has two separate injections. One is only for the starting up and the other for the engine running after that.
It seems to me that your problem is related to the above switching.
Last edited by jaaa; 10-18-17 at 12:41 PM.
10-18-17, 05:58 PM
#6
Moderator
So there's no more problem. But I worry about it's coming back again at middle of no where.
I think I'd better inform you what I have experienced. Several years ago, my local shop owner asked me for a help having exactly the same problem with yours. The engine started up easily but quit running in a few seconds to several seconds. The accelerator didn't respond at all. The shop owner diagnosed it but there was no code and thought it was caused by the fuel pump. He replaced it but nothing was changed. He used a known good ECU but still the result was the same. He had no more idea and he decided to call me.
The engine continued to run as long as the starting fluid is sprayed and I found it not a ignition issue but a switching issue of the fuel supply. As I checked the injection signal, it became extremely short after the start up. The switching signal was sent from the ECU but the width of the signal was less than 1 msec. The problem was caused by the dead air flow meter, I finally found. It was reporting the ECU that there was no air coming in and the ECU minimized to drive injectors. Thus the engine couldn't continue to run.
I suggested shop owner to replace the air flow meter and also demonstrated a method to use a potentiometer and a DC power supply. I used those to make and send the pseudo signal to the ECU informing that the air is coming in. Doing so the engine continued to run and the shop owner nodded. He was a little amazed at the trick but it was a common way for me. Electric signals can be often made using a potentiometer. You also can cheat the ECU by this way.
I think I'd better inform you what I have experienced. Several years ago, my local shop owner asked me for a help having exactly the same problem with yours. The engine started up easily but quit running in a few seconds to several seconds. The accelerator didn't respond at all. The shop owner diagnosed it but there was no code and thought it was caused by the fuel pump. He replaced it but nothing was changed. He used a known good ECU but still the result was the same. He had no more idea and he decided to call me.
The engine continued to run as long as the starting fluid is sprayed and I found it not a ignition issue but a switching issue of the fuel supply. As I checked the injection signal, it became extremely short after the start up. The switching signal was sent from the ECU but the width of the signal was less than 1 msec. The problem was caused by the dead air flow meter, I finally found. It was reporting the ECU that there was no air coming in and the ECU minimized to drive injectors. Thus the engine couldn't continue to run.
I suggested shop owner to replace the air flow meter and also demonstrated a method to use a potentiometer and a DC power supply. I used those to make and send the pseudo signal to the ECU informing that the air is coming in. Doing so the engine continued to run and the shop owner nodded. He was a little amazed at the trick but it was a common way for me. Electric signals can be often made using a potentiometer. You also can cheat the ECU by this way.
10-19-17, 06:46 AM
#7
Lead Lap
Thread Starter
So there's no more problem. But I worry about it's coming back again at middle of no where.
I think I'd better inform you what I have experienced. Several years ago, my local shop owner asked me for a help having exactly the same problem with yours. The engine started up easily but quit running in a few seconds to several seconds. The accelerator didn't respond at all. The shop owner diagnosed it but there was no code and thought it was caused by the fuel pump. He replaced it but nothing was changed. He used a known good ECU but still the result was the same. He had no more idea and he decided to call me.
The engine continued to run as long as the starting fluid is sprayed and I found it not a ignition issue but a switching issue of the fuel supply. As I checked the injection signal, it became extremely short after the start up. The switching signal was sent from the ECU but the width of the signal was less than 1 msec. The problem was caused by the dead air flow meter, I finally found. It was reporting the ECU that there was no air coming in and the ECU minimized to drive injectors. Thus the engine couldn't continue to run.
I suggested shop owner to replace the air flow meter and also demonstrated a method to use a potentiometer and a DC power supply. I used those to make and send the pseudo signal to the ECU informing that the air is coming in. Doing so the engine continued to run and the shop owner nodded. He was a little amazed at the trick but it was a common way for me. Electric signals can be often made using a potentiometer. You also can cheat the ECU by this way.
I think I'd better inform you what I have experienced. Several years ago, my local shop owner asked me for a help having exactly the same problem with yours. The engine started up easily but quit running in a few seconds to several seconds. The accelerator didn't respond at all. The shop owner diagnosed it but there was no code and thought it was caused by the fuel pump. He replaced it but nothing was changed. He used a known good ECU but still the result was the same. He had no more idea and he decided to call me.
The engine continued to run as long as the starting fluid is sprayed and I found it not a ignition issue but a switching issue of the fuel supply. As I checked the injection signal, it became extremely short after the start up. The switching signal was sent from the ECU but the width of the signal was less than 1 msec. The problem was caused by the dead air flow meter, I finally found. It was reporting the ECU that there was no air coming in and the ECU minimized to drive injectors. Thus the engine couldn't continue to run.
I suggested shop owner to replace the air flow meter and also demonstrated a method to use a potentiometer and a DC power supply. I used those to make and send the pseudo signal to the ECU informing that the air is coming in. Doing so the engine continued to run and the shop owner nodded. He was a little amazed at the trick but it was a common way for me. Electric signals can be often made using a potentiometer. You also can cheat the ECU by this way.
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10-19-17, 09:50 PM
#8
Moderator
You are welcome jaaa. There is one more item I'd better to inform you.
It's about the operation of the fuel pump. It works fully at the start up. As you see the wiring diagram at the link below, the fuel pump relay supplies the DC12V directly to the fuel pump and it works fully at the initial start up. But once the engine is started up, the relay switches the contact and the fuel pump gets less power via the fuel pump resistor and works a bit weakly. It works fully again when the load is big such as to climb up hills or to run very fast being switched the contact by the ECU.
https://www.clublexus.com/forums/ls-...m-problem.html
When the resistor is open or the contact is not in good conditions, the fuel pump can't get the power and there's no fuel supply to injectors. In this situation, the engine can't continue to run too.
It's about the operation of the fuel pump. It works fully at the start up. As you see the wiring diagram at the link below, the fuel pump relay supplies the DC12V directly to the fuel pump and it works fully at the initial start up. But once the engine is started up, the relay switches the contact and the fuel pump gets less power via the fuel pump resistor and works a bit weakly. It works fully again when the load is big such as to climb up hills or to run very fast being switched the contact by the ECU.
https://www.clublexus.com/forums/ls-...m-problem.html
When the resistor is open or the contact is not in good conditions, the fuel pump can't get the power and there's no fuel supply to injectors. In this situation, the engine can't continue to run too.
10-19-17, 11:53 PM
#9
Lexus Champion
First off, this is about my grnadsons 1991 lexus ls400, not my 1996. He called me last night and said his car wouldn't start, so I brought my basic tool box and volt meters with me. I got there and found out it would start fine and then die within seconds of running. I must have tried starting it about 25 times with no success. It also didn't seem to have any throttle response in the short time it was running, the rpm wouldn't go up if you floored it. I did notice that after it died, the engine oil light would come on(like it should on a killed engine) but also the coolant light came on. I checked and sure enough- the coolant in the overflow was very low. You could barely see it at the bottom of the tank. I went home and came back and filled to between the two lines. I tried starting it again, but it died like before. I tried it again, but while it first started, I went to neutral and revved it and for the first time it responded to the accelerator and continued running. After it started, it continued to work normally on all further start attempts. Could a coolant sensor on top of the engine caused this because of low coolant? My son-in-law is leery now of letting his son drive the car and I'm trying to figure out a plausible reason for the fix(?) I did on the car.
The earlier (1990-1994 LS400) had better quality engine harness connectors, but negative battery terminal to ground battery cable is suspect...including engine grounding points...
Age-related resistance with resulting voltage drop is bound to occur with vintage wiring
Check out my postimg on negative grounding issues
Your positive batteey terminal clamp is probably due for replacement.
Check out my posting on positive battery clamp.replacement.
Last edited by YODAONE; 10-20-17 at 12:00 AM.
10-23-17, 03:07 PM
#10
Driver School Candidate
Join Date: Jan 2017
Location: OH
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Hey guys, I'm new here but not to forums. Came across this post as I have a the same issue on my 96 LS400(240K). This happened to me out of the blue. car ran GREAT for 3 days and then this. Now reading the post I see the word MAF "meter" and at the sake of sounding dumb is this different from the MAF sensor? Just want to clarify that they are or are NOT one in the same part. When the rain stops I'm going to tackle this project myself. I had a mechanic come check it. He got the car running but at the cost of $225, replacing plugs and few minor things. Car ran ok for the rest of the day and then this morning I come out to go to work and back the start up and die issue.
10-24-17, 10:47 AM
#12
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I do have CEL and flashing trac light. No reader to check codes. The mechanic had one but didn’t share his findings other than to tell me a cyl 4 misfire. I’m getting a reader to check myself.
10-26-17, 08:41 AM
#13
Lead Lap
Thread Starter
Yamea or someone with ECU knowledge
I pulled an ECU out of a pick pull to change caps for this problem car. I didn't notice that it had a different part number. The one in the car is 89661-50032. The one I pulled from the pick pull has a part number of 89661-50042. From what I can see, the one from the pick pull has traction control and the original doesn't. Can I use it anyway? Or would that cause problems?
10-26-17, 09:09 AM
#14
Moderator
I pulled an ECU out of a pick pull to change caps for this problem car. I didn't notice that it had a different part number. The one in the car is 89661-50032. The one I pulled from the pick pull has a part number of 89661-50042. From what I can see, the one from the pick pull has traction control and the original doesn't. Can I use it anyway? Or would that cause problems?
10-26-17, 11:03 AM
#15
Lead Lap
Thread Starter
Well, I went ahead and just tried it and the traction control ECU appears to work just fine with the non traction control car. I was afraid it might set some kind of CEL or something. At least it hasn't done it yet. I'll recap the original one tomorrow and see how that goes. That makes three ECU's I've replaced caps on without bungling the job(I guess my US Navy training didn't go for naught). Thanks for the heads up on JDM and Celsior, looks like it works on USA models too.