Rmmccarthy

I'm not sure if this is a similar problem but the connector is a 2 wire just in front of the diag connector in engine bay under front of fuel rail next to a 5 wire connector I had a leak on coolant hose under idle air valve I believe led to corrosion and poor connection I diagnosed with a "wiggle" test while running I moved various wires and connectors and found this hope it helps I should add that I have already upgraded ecu caps

oldskewel

iTrader: (1)

Here's a troubleshooting thing you can try next time it flakes out. This works on my '91, so it should on yours too.

1. Pop off the cap on the gray rectangular diagnostics port in the engine bay
2. Use a paperclip to jumper the two rear corner pins (rear means toward the rear of the car)
3. That will cause the fuel pump to run at full power all the time, when the ignition is ON. This bypasses the control circuit and fuel resistor, which are smart enough, if working properly, to know when the fuel pump can run at a slower rate.

So if that fixes your problem, then you can start looking into those features as the cause.

I've read about people running that way for years before the fuel pump burns out. So it would not be a problem, I think, if you want to just leave it jumpered to rule out those items until you get this problem figured out.

Also, while on the topic of easy things to do, you might want to run with a 50% or higher fuel tank level. Just to rule out some problems that are rumored to sometimes appear when the fuel level is low.

dicer

So the connector is under the idle air control? What does it go to?

pacerdonfl

Hi - I had an earlier thread about this - thought it might be getting to long/deep. Some good suggestions but no resolution so far.

NOW - it Starts up and runs beautifully for 45 seconds, then slowly starts to lose rpm's...then after almost quitting, will jump back to a smooth idle....then in 10-20 seconds later, slowly lose rpm and then either die, or jump back up to smooth idle....

When it dies, I can start it back up easily, runs nicely for 30 seconds, then back into the cycle of slowly stalling out and or then jumping back to nice idle .... it will eventually die within 2-4 cycles of this.....

Arrrrghhhhh!!!!! - help please / also - no check engine indicator.....


Thanks much!
/Don



This was my earlier post - thanks to all for suggestions.
91LS400-Stalls after 15 minutes, Starts, Idles/runs beautifully when running

Yamae

You'd better check the fuel pressure.
If you can't do it quickly, simply bypass the fuel pump resistor to see the difference.

oldskewel

iTrader: (1)

And that procedure I mentioned in post #17 does that (bypasses the resistor), right?

pacerdonfl

I have another good working 91 ls400- from it i have swapped both fuel pump resistor, the fuel pump relay to the stalling car, and still no change. Runs then slowly stalls, cycles 3-4 times, then finally dies. I have also replaced the fuel pump filter.

This stalling ls400 has only 140k miles and supposedly had a dealer 100k service....

Thanks for more thoughts / don

pacerdonfl

Yesterday I started it in the driveway about 5 different times - starting perfectly, but would then cycle from smooth idle to almost stalled and back to nice idle... then eventually die. Sometimes 1 or 2 cycles, sometimes as many as 5 times. This same scene happened all 5 times during the day that I tried starting it.

Today I started it up, moved it 30 ft in the driveway, and left it idling in park - after 45 minutes, came out and ran it up a couple of times to 2000 rpm and back....no stalling. I then turned it off.

It's driving me nuts it's so intermittent w/no chk engine light.

It's not the fuel filter, fuel pump resistor or fuel pump relay. Also jumped the pins in the diagnostic bundle that causes the fuel pump to operate full power - no change.

Any ideas please???

/Don

joeyb

A few years ago, BMW 7s had a similar issue. It turned out to be spiders would nest in the fuel tank vent line (really) and would create a vacuum in the fuel tank.
I doubt you have spiders, but try this experiment. Try running it with the fuel cap loose, or immediately after it shuts off remove the cap to see if it sucks air.

dicer

I think what ever causes these problems may be something different in the different cars.
Don, have you done anything with the cam or crank sensors?
I think the fuel pressure test is a good idea, you could have a pressure regulator or damper problem, like its taking away fuel then it comes back. The warming up type problem is more something with sensors that come online after warm up or during it. If I figure out what my problem is I'll post it. It would not be fun being 200 miles from home and have this come on suddenly with no resolution.
Since the OBD1 cars don't show much of anything on a scan tool, I'm not sure if the top of the line ones show more. This makes it more difficult to figure stuff out. A person would need to have a good collection of test equipment hooked up to check all the signals to try to track this down.

dicer

Anyone with this problem try disconnecting the small vacuum hose from the EGR, that is the one near or in front of the PCV hose. Let me know what happens.

jscoda

The car starts to spudder.....try to give it more fuel since such a low rpm then the rpm jump but not over 2000 like a limiter cuts in to protect the engine. Then rpm go between 200 to 800 and jump back and forth. Car shutters more then shuts off. BUT sometimes the car runs just fine like nothing is wrong at all. I mean for days at a time. Other times the starter wont catch and have to turn the ignition switch over and over till it turns the starter and starts.. My first guess was the starter but when it does turn over the car wont start at times. Then I thought fuel pump but I smell raw fuel.
Haven't tried the mass air. Hate to throw parts at it but am looking to sell it but its gotta run for someone to want to buy it.....guess I need a laundry list of things to try.

Any help would be great.

sndlight

Check the ECU thread. Your symptoms reek of bad ECU caps.

pacerdonfl

I removed the fuel cap - the car has been running flawlessly for 2 days....??? Where is the fuel tank vent line?

As I understand, these tanks should have a positive pressure - what creates that pressure? How is it possible to have a vacuum then???

Thanks,

/Don

dicer

Evap system is the fuel tank vent, the caps can't leak if they do they throw a code on obd2 systems. For emissions no fuel vapors are suppose to leak out of a vent system. Good find though.

Okay a correction, the fuel cap has a vent hole and a check valve that lets air in when the tank has a vacuum and closes when there is pressure in it.

I was thinking of obd2 systems. The LS400 manual shows a check valve in the fuel cap so that system can't do the vacuum test.