1997 Ls 400 Won't Rev Beyond 4000

[MUDGUTS]

Hello from England,

I am looking for any help or suggestions regarding a 1997 LS 400 I have that doesn't want to rev past 4000.

The whole sorry tale is at: The UK Lexus Owners Club

Basically the car will let me rev it to the red line either steadily or by 'blipping' the throttle but if you push the accelerator pedal to the floor the revs will drop to 4000 and it then stays there as long as your foot is planted, once you lift your foot, the revs can rise again. The car will run perfectly on the road until you floor the throttle pedal then it will kick-down a gear or two but seems to limit itself at 4000 RPM again, once you release your foot the box changes up and off you go...

The updated list is below of things already checked / to check:

Already checked:

Exhaust & Catalytic Converters checked

Valve timing checked

EGR valve cleaned & checked

Throttle Body & Plenum Chamber cleaned

Distributor Caps, Rotor Arms & HT Leads replaced (Old Spark plugs were not suspect so replaced after new ones tried)

Engine sensor connections checked

Gearbox shift position sensor (confident this isn't at fault)

Fault code 21 cleared with new Oxy Sensor

Fault code 28 cleared with new Oxy Sensor

Throttle position sensor checked

MAF Sensor unpugged: Check engine light is on, engine runs rough and won't rev up much

Battery off for 30+ mins: Was disconnected at the dealers

Air Filter replaced

MAF Sensor (another one tried), this would be the third on the car

A temp sensor or faulty water pressure cap (I'll discount these as just about everything like this has been checked now)

Coil Packs

To Check:

ECU

A new theory: Some kind of fault with the gearbox and kick-down switch / sensor / wiring

The car is now with a 1UZ-FE specialist in the UK. They have pretty much tried everything and we are now down to the ECU or a fault with the gearbox.

All contributions welcome

[MUDGUTS]

Well, there is nothing wrong with that engine.

It's been with Thor Racing at Coventry, who have gone well above the call of duty and comprehensively checked out the engine and systems. Just about everything has been checked and analysed, most of the list below re-checked and also: Ignitor swapped for a known servicable unit, same with the ECU, Throttle Position Sensor, Fuel pump and control, etc.

Time was running out, so I have the car back now and will run it for a while.

One last theory is that the car seems to go into a self imposed limit of 4000 RPM. The tech at Thor and I (whilst on the way home), note that when the throttle is floored and the car reaches this 4000 RPM limit, moving the shift lever has no effect, I had it in 'D' '3' 'L' and even 'N' whilst it kept driving along. As soon as you lift off and it comes out of this region, you can move the shift lever and the box shifts accordingly.

The updated list is below of things already checked / to check:

Already checked:

Exhaust & Catalytic Converters checked

Valve timing checked

EGR valve cleaned & checked, pipes also checked

Throttle Body & Plenum Chamber cleaned

Distributor Caps, Rotor Arms & HT Leads replaced (Old Spark plugs were not suspect so replaced after new ones tried)

Engine sensor connections checked

Gearbox shift position sensor (confident this isn't at fault)

Fault code 21 cleared with new Oxy Sensor

Fault code 28 cleared with new Oxy Sensor

Throttle position sensor checked

MAF Sensor unpugged: Check engine light is on, engine runs rough and won't rev up much

Battery off for 30+ mins: Was disconnected at the dealers

Air Filter replaced

MAF Sensor (another one tried), this would be the third on the car

A temp sensor or faulty water pressure cap (I'll discount these as just about everything like this has been checked now)

Coil Packs

ECU

To Check:

Gearbox

[VBdenny]

Not sure about a 97 but my 90 has a button underneath the accelerator that kicks the car to WOT when floored. I don't know if it has anything to do with your puzzling problem but looking at everything you have checked, seems like any suggestion is good.

[SRK]

Many of the items you've listed will produce a trouble code. With swapped ECU's and no code, I can only think that the problem is not one that produces a code. And as you've not listed any check of the fuel pressure in the rail, I'd check fuel pressure.

Of course, from this distance I'm just guessing....

[MUDGUTS]

Thanks Gents. KD switch works OK and the fuel pressure has also been looked at, the specialists had a go at bumping up the voltage to the fuel pump as it has two different pressures it runs at.

It seems to sense a high demand for fuel or something like that and cuts the fuel off if you punch the throttle...

I'm probably going to have to live with this now, this car cost less than £900 but I have spent another £1400 or so just trying to diagnose what the fault is. Having said that, the car is in very good condition, there are no knocks, bumps or problems with the suspension, it drives straight, etc. Some of this money has been spent on replacing faulty components such as Oxy Sensors and cleaning out throttle body, EGR system, etc. Also the Rotor Arms, Distributor Caps and HT leads have all been replaced.

Four things are remaining to fix:

Loose wiper blades (require a new motor and will eventually get around to replacing this but can live with it)

I need to re-fit one of the headlamp washers (just requires a little time)

The radio lights need replacing (been quoted £70, once radio is removed, which I can do)

The Drivers heated seat doesn't work (this I can live with)

Other than that lot, I can service it or have an independant do some of this.

On the drive back last night I learnt that I can probably adapt my driving style to get around this problem: By using the ECT Power mode and knocking the overdrive off by using '3' rather than 'D' I can get this car to give adequate performance.

Once I get a chance I will be looking at the Gearbox conections though, as I think this is pretty much the end of the line as far as enquiries go. Once that is eliminated I'll probably live with it until I change for a LS 430.

[MUDGUTS]

...Just one thing, I have thought of is a faulty Knock sensor?

[SRK]

I've never heard of a fuel pump that changes pressure by voltage. In every case I know of, it's done with a pressure regulator, and that may or may not have a manifold pressure diaphragm to change pressure with engine load. Modern engines no longer use manifold pressure adaptation in most cases.

I have certainly seen many engines that appear to limit rpm due to weak fuel pumps which can produce pressure but not volume. When volume goes up, pressure drops. A good technician would scan the pump for rpm and current draw - those figures are usually not published, but experience will show when a pump is failing.

It needs to be driven with the pressure gauge hooked up so that it can be observed under all conditions. Simply checking at idle will not do.

Whatever the problem is it is simple. I wouldn't be satisfied with driving around the issue.

[MUDGUTS]

I've never heard of a fuel pump that changes pressure by voltage. In every case I know of, it's done with a pressure regulator, and that may or may not have a manifold pressure diaphragm to change pressure with engine load. Modern engines no longer use manifold pressure adaptation in most cases.

I have certainly seen many engines that appear to limit rpm due to weak fuel pumps which can produce pressure but not volume. When volume goes up, pressure drops. A good technician would scan the pump for rpm and current draw - those figures are usually not published, but experience will show when a pump is failing.

It needs to be driven with the pressure gauge hooked up so that it can be observed under all conditions. Simply checking at idle will not do.

Whatever the problem is it is simple. I wouldn't be satisfied with driving around the issue.

Thanks for the input SRK

The car will run past 4000 RPM but I have now discovered but to do this I have had to put it into '3' or it's a bit to fast for out British roads but it will go past. The issue is that if you punch the throttle, either the fuel is cut or something happens that is so dramatic that the power drops right off. If you punch the throttle below 4000, it just sits there like a limit.

So it must be getting enough fuel at high RPM.

[SRK]

Has the secondary ignition been observed on an old style automotive oscilloscope? Almost sounds like coil saturation.

I'm certainly keen to hear what the problem was once it's fixed. It's a tough one for sure.

[MUDGUTS]

Well, I have done over 10,000 miles in this car now with no change to the original symptoms.

It's had 4 new tyres and is still driving nicely.

No fault codes have ever appeared.

I fixed the loose wipers with a replacement wiper motor (thanks benfur) and apart from a replacement temp sensor and a couple of bulbs, it's given no problems.

Regarding this 4000 RPM problem: I have a sneaky suspicion it's the knock sensors, I'll be considering getting this looked at.

As always, any contributions welcome

[MUDGUTS]

I've never heard of a fuel pump that changes pressure by voltage. In every case I know of, it's done with a pressure regulator, and that may or may not have a manifold pressure diaphragm to change pressure with engine load. Modern engines no longer use manifold pressure adaptation in most cases.

I have certainly seen many engines that appear to limit rpm due to weak fuel pumps which can produce pressure but not volume. When volume goes up, pressure drops. A good technician would scan the pump for rpm and current draw - those figures are usually not published, but experience will show when a pump is failing.

It needs to be driven with the pressure gauge hooked up so that it can be observed under all conditions. Simply checking at idle will not do.

Whatever the problem is it is simple. I wouldn't be satisfied with driving around the issue.

...Well gents, I have done over 22,000 miles since purchase now and finally there is something that approaches a symptom manifesting itself:

I have quoted SRK above as the symptom I get now (nothing else has changed apart from this, the car stil drives OK) is a high pitched whine from the rear: Sometimes as I first pull away and now I can re-produce it when I accelarate hard but as soon as I come off the throttle, the noise stops. It's like the noise is from a fuel pump or some similar component straining...yet the car starts and runs fine.

[curiousB]

I think SRK gave you some important clues a while back. Testing engine revs in neutral or park isn't a very meaningful test on the fuel system. It may be useful to check ignition (erosion of spark output at high RPM) and see if there are coil and/or ignitor problems though. Never cars have REV limiters to stop RPMs past a certain level. Its controlled with software in the ECU. Not sure what the ceiling is on these cars.

For fuel system volume/pressure the engine needs to be under load. Is there a way you can connect a fuel pressure gauge to the fuel rail and tape the gauge to the windshield (dial facing inwards) and go for a short ride? See if the pressure is maintained under load conditions (heavy acceleration, highway speed acceleration). The whining sound has to be fuel pump related. If you change pump I'd change inline fuel filter for good measure.

Also I should mention there is a fuel pump relay in the electric circuit to the pump. It switches in and out a series resistor to limit current to the pump motor. If the relay is stuck such that the resistor is never shorted (bypassed) the pump may have volume problems at high demand. A simple test would be to short the resistor with a jump wire and see if the symptoms change.

Are you trying to race a LS400?!?! Not really the target application of this lumbering comfy couch on wheels.

Have you really spent £1400 in repairs on a car worth £900? Yikes, that could have been many Guinness's.

[MUDGUTS]

Thanks for the input CuriousB. The voltage to the pump was checked a while back and its getting the correct boost of voltage. Also by driving it around I can cause the noise but creating high demand (flooring the throttle under load) so I think everything up to the pump is good, I wonder if the noise is the pump struggling to meet the demand and maybe it has never been that strong.

Not trying to race the car BTW and for the money I,ve spent in total, some of which has been on tyres, etc. tha car has given good service.

[curiousB]

The voltage to the pump was checked a while back and its getting the correct boost of voltage. Also by driving it around I can cause the noise but creating high demand (flooring the throttle under load) so I think everything up to the pump is good, I wonder if the noise is the pump struggling to meet the demand and maybe it has never been that strong.

Noise isn't typical so it could be a warning sign the pump is on its last legs. A blocked filter could be adding load to the pump as well. A worn pump will show its problems by not being able to sustain required pressure at higher volume flow. This is the WOT case you are having troubles with. Curbside fuel pressure measurement can be deceiving. Maybe there is enough evidence to just swap out the pump and filter rather than spending ££££ on test equipment to sort it out.

[MUDGUTS]

Have done a bit more research and by jumping FP and +B in the Diagnostic port the pump gets a higher voltage, so I'll do this next chance I can and see if it reproduces the noise I'm hearing.

[landar]

Interesting dilemma. You sure have covered a lot of bases in trying to pinpoint this issue. My 'Yank' mind cannot get past the clues you have given on the accelerator pedal. You say that feathering the pedal can get you past 4k RPM, yet tromping on the pedal limits the engine to 4k. I would like to explore that area further. I am wondering if there is an issue with the Thottle Position Sensor or Accelerator Position Sensor. I know, you have checked those items off of your list. Still, I wonder if there is not some 'dead' spot on a position sensor resulting in the ECM throttling back the engine. Would you be game to try a rather crazy test? Limit the travel of the accelerator pedal such that it cannot actually touch the floor even when you mash it all the way down. Perhaps a small board(cardboard or wood) placed betwixt the pedal and floor to limit the full travel? This it just a short term test. I would like to know if there is some sort of dead zone in the latter part of the throttle response. With a small limit on the pedal travel, could you consistently get to, say, 5k RPM? Does this make any sense or have I misinterpreted your previous statements?? ^_^

[MUDGUTS]

Thanks for the input Landar, I'm pretty sure it's not the above. One of the things the specialist did was to swap those components for known servicable ones and the fault was still there.

It is definately related to demand, so if I allow the speed to build up it will pass 4000 RPM but by placing a large demand on the engine by punching the throttle for example, the result is it digging in its heels. There is some mechanism that either stops extra fuel or does something with the ignition (hence the suspicion of knock sensors).

I have tried jumping FP and +B in the diagnostic port and the pump does seem to get a higher voltage, you can definately hear it then but otherwise it is silent. It certainly sounds like the noise I'm hearing.

Obviously this could be a red herring but I won't know until it's changed. The dilema is that this car is getting quite old now and I'm very reluctant to spend any money on it. My strategy now may be to run it until that pump fails and then have it replaced. If that fixes the fault, that would be great but I won't put any more money into it unless it needs it to keep it on the road. If the pump replacement is expensive, that would be the end for the car.

[landar]

Fair enough, Phil. You certainly have gone over that engine with many different approaches and in all truth, nothing should be wrong. Yet it is. It may be time to go over some of the obvious again as they may have been deemed 'good' but on second check, found to be faulty afterall. Now, you could get a scan tool and check the system. Not a simple OBDII reader. The scan tool gives you many more parameters. Your issue is really fairly basic and yet the problem area has not yet been pinpointed. To wit...you command the engine to a certain range via the throttle, the engine responds and produces the desired output. If it were mine, I would want to verify that the engine is indeed being commanded and if not, why. If so, why is the engine not responding? Fuel delivery lean/rich, timing retarded, etc. A scanner may help you glean that information and greatly narrow the search.

As far as the knock sensors, have you tried a high-octane fuel or octane booster, to see if that might help (if only for a test). Again, knowing the timing at higher RPMs would verify this but requires instrumentation.

[MUDGUTS]

Sadly, mine is only OBD 1 (have double checked) and you are right, if the car was fitted with OBD 2 this would have probably have been diagnosed by now. With regard to the octane booster, this is something I thought about but never did, again due to trying to limit the expenditure. I could have had the knock sensors replaced but that would be more cost and they haven't produced a fault code. I checked today using the 'Flash' method in the OBD 1 socket and nothing comes up, in fact the only fault codes this car ever produced were for Oxy sensors, which were replaced.

I could send it to the specialist one last time if the pump does look like failing and have that done, as the car is otherwise a good runner and has a valid MOT test until September, once there I could allocate another £100 to get it on the dyno there and let them mess around. Apparently it may be possible to see if the ignition is being affected when this glitch occurs: That would point to the knock sensors.

[SRK]

As I mentioned months ago you need to have the fuel pressure checked. Hook up the gauge, tape it to the windshield and drive the car. If the gauge is steady at the correct pressure, then the secondary ignition should be placed on a 'scope.

You're looking for something that doesn't produce a code - that means it isn't a sensor that is monitored and something that affects all cylinders equally.

[MUDGUTS]

As I mentioned months ago you need to have the fuel pressure checked. Hook up the gauge, tape it to the windshield and drive the car. If the gauge is steady at the correct pressure, then the secondary ignition should be placed on a 'scope.

You're looking for something that doesn't produce a code - that means it isn't a sensor that is monitored and something that affects all cylinders equally.

This is a good suggestion but I don't have a guage otherwise I would do this. The issue I have is that whilst a good car, I just cannot justify any more expense unless it cures an existing fault and is not too much to fix.

Anyway, this evening the whine is not only still there but seems slightly louder, so I conducted a bit of research: The noise ocurs just after start and definately when I floor the throttle, it will stay on, whining away, until I take my foot off the pedal. At the same time the engine will hold back as always, so the noise and the engine holding back are happening at the same time.

Also I tested the system that ups the pump voltage again by jumping FP and +B in the diagnostic port and the pump does seem to get louder, it's not so pronounced if the engine is off but with the engine running, the noise I hear is the same as described above, so now I can be fairly sure that the whining is from the pump working harder. My theory now is that the pump was never powerful enough to supply the extra fuel demanded and that leads to the engine holding back somehow.

I'm going to get a new pump tomorrow and have it fitted as soon as possible. I'll try to keep the old one to carry out an autopsy on it and will post up the results.

[curiousB]

Its a reasonable assumption that a worn pump can't meet pressure and volume at higher fuel demands (WOT). Other supporting data is the noise which is not normal. The jumper of the FP/+B port is just shorting out the series resistor so the pump sees full 13.3V instead of something less.

A fuel pressure gauge isn't very expensive but it doesn't sound like you'd use it much. I bought one 2 years ago and still waiting to crack it out of the carton.

[landar]

Phil, a lot of information is just not adding up. You say your 97 LS400 is OBDI???? I thought 95 and up was OBDII?

You also say in earlier UK posts that you can put the tranny in Neutral, floor it and the engine will limit to 4000 RPM. While a weak fuel pump might limit the engine performance under load, It seems to me that the engine would not limit to 4000 RPM in 'N' simply because of a pump. However, it might be some rev limiter kicking in. And maybe that same limiter is inadvertently kicking in while in 'D'?

[MUDGUTS]

Hello landar,

Apparently OBD2 came in earlier in the USA than Europe, we got it later. I definately have OBD 1 though, sadly.

What I have said before still stands, if I put the tranny in Neutral and floor it the engine will limit to 4000 RPM but by 'blipping' I can get the RPM up and I have had it higher whilst driving, so it doesn't seem to be a hard limit.The more I think about it, the more this problem occurs when extra fuel is demanded.

Some time back I updated the thread on the UK forum with this:

Driving home on the motorway recently, I thought the issue had gone away, when I floored the throttle, the car responded instantly, whereas normally it seems to trim back the fuel, as if taking your foot OFF.

2 days later I tried flooring it again and the car dropped a gear and the RPM went to about 5000 and swung about wildly while the car stayed at its current speed. Once I took my foot off the throttle, it changed up and carried on as if nothing had happened.

I'm dropping the car off for the pump to be replaced later, so should have the car back by the weekend. If the problem is still there, I know it's not that.

[SRK]

Whoever is replacing the pump should have the gauge to check fuel pressure - it's a simple hook-up. If the pressure is good during this "self-limiting" period then you know it isn't the pump, and you can save that money for the real problem. If not, it's the pump.

The pump should be replaced because it is diagnosed to be bad, not because it is suspected so.