Ls400 Dies When Given Gas

[mrsrt8]

So I as driving along to school one day, and after I passed over a bump, my 1996 LS400 died on me. We checked the fuel pressure and it was normal. After going over the bump, the car would not start. The distributor caps are brand new, the spark plugs are brand new as well. We replaced the fuel pump ecu capacitors with no avail. We tested the ecu in another ls400 and the car started and worked perfectly. Now the car will not accelerate , but it idles. Im open for discussion.

p.s it has 201000 miles

[landar]

You are open for discussion? Good. Me too. ;)

First off, I would not put to much emphasis on the bump. Could be simple coincidence.

Now, will the engine rev properly and normally while in Park(I am talking about taking it smoothly up to 4k RPM's) or does it die with no load?

[mrsrt8]

The car doesnt rev at all, it dies with no load

[mrsrt8]

So

The car doesnt rev at all, it dies with no load

Sorry i meant it dies right when you give it just the minimal amount of gas

[landar]

So, several easy things to try. Get a can of starter fluid and 'spritz' a little bit of that into the intake snout(probably be easiest to spray directly into the throttle body..be careful and use it lightly, very flammable of course) to see if you can 'nurse' it above an idle. If you can, then you have a fuel delivery problem. Alternatively, you could check for spark using a timing light. Observe sparking at idle then simply give it some throttle. If the sparking dies, then its an ignition issue. You will need to check each coil, repeating the test.

Simple, yet useful tests in the next step of action.

[mrsrt8]

So, several easy things to try. Get a can of starter fluid and 'spritz' a little bit of that into the intake snout(probably be easiest to spray directly into the throttle body..be careful and use it lightly, very flammable of course) to see if you can 'nurse' it above an idle. If you can, then you have a fuel delivery problem. Alternatively, you could check for spark using a timing light. Observe sparking at idle then simply give it some throttle. If the sparking dies, then its an ignition issue. You will need to check each coil, repeating the test.

Simple, yet useful tests in the next step of action.

The spark plugs and ingintion coils were replaced, but I havent tried the STarting fluid , i will attempt it soon, and report back

[landar]

Keep in mind that although you replaced the plugs and coils, that does not clear the ignition side. Could still be many other electrical things..sensor/ECU/ignitor/connector issue.

[mrsrt8]

we checked the voltage and tried everything everyone here said, with no avail

hope is not lost :)

[fsuguy]

Hi,

This may be a long shot, but if the bump was significant in the issues you describe, it could be a ground wire knocked loose. Yo may be able to get a schematic of all the ground connections and check through them one by one to eliminate that possibility. Alterntively, it could be some crud clogging up the filter/pump, and while flow may be enough to idle the engine, it may not be enough to sustain higher RPMs. One other thing that comes to mind is the Throttle Position Sensor may have a flat spot on it, or it may be going south. Testing with a known good one will eliminate that as a source of problems.

Hope this helps.

[mrsrt8]

Hi,

This may be a long shot, but if the bump was significant in the issues you describe, it could be a ground wire knocked loose. Yo may be able to get a schematic of all the ground connections and check through them one by one to eliminate that possibility. Alterntively, it could be some crud clogging up the filter/pump, and while flow may be enough to idle the engine, it may not be enough to sustain higher RPMs. One other thing that comes to mind is the Throttle Position Sensor may have a flat spot on it, or it may be going south. Testing with a known good one will eliminate that as a source of problems.

Hope this helps.

I'd like to note that the car was idling a bit too fast, I will try the TPS replacement and look for a ground wire schematic

[mrsrt8]

tried it doesnt work

[landar]

So the engine starts and idles...all while the transmission is in Park. Now, if you simply put it in Drive, does the engine die as the transmission engages or does it continue idling (and at what RPM)?

[fsuguy]

...couple additional things, and some of the more experienced engineers can chime in anytime -

If the car idles more or less fine, but dies when given gas, then two possibilities exist:

a. It is not getting enough fuel to combust the higher air volume mixture (too much air volume for the metered fuel), or

b. Spark strength is not enough to combust the denser mixture (I think this is a very low probability), so...

Do a vacuum test...the idle too fast is symptomatic of higher than normal volume of air - possibly a vacuum leak - do the test and verify the correct level of vacuum - there should be a number available. If the vacuum is too high, you have a significant leak and when you open the throttle too much air is killing the engine. Possible areas to check are the accordion style connector to the air intake on the manifold - cracks develop in the folds and are not readily visible without taking it off and risking cracking them, anyway, the three thin hoses on the TB, and if you still them attached, the PS vacuum hoses. These are common areas where you may develop leaks. The bump may have jarred a relatively loosely clamped hose and now you are experiencing the leak - if that is the problem. Of course, if you have not ruled out a loose ground wire, you will experience all sorts of weird problems, since the ECU must have its grounds for all the sensors for the circuitry to operate optimally.

One final after-thought check the connector on the MAF to see if it is tight - should not cause the engine to die, though.

Good luck and hope this helps.

[mrsrt8]

PROBLEM SOLVED!!! :D

Finally after 6 months without my favorite ca in the world, a trusty mechanic in new york told us that the OEM timing belt that another mechanic installed was bad. After further investigation, the engine was wildly out of time. So onward to replace the timing belt and tensioners. It is now idling at 650rpm, and it pulled a camshaft sensor code, we replaced them.

Thanks to all who have helped me through this crazy experience!

[fsuguy]

Hi,

Glad you have your wheels back, and working well. Also, thank you for posting your solution - it helps us all!!!