Odd loss of power?

[DAMINK]

Hey chaps. A bit of a weird problem i just encountered and wondered if anyone had any ideas.
My car is a 1994, Disco 1 3.9 v8 Auto.

What i did before it happened. (car was running perfect on petrol before).

Changed an intake manifold for another i had which has gas injected.
Changed the Stepper motor housing as the one i put on has 2 vaccum points instead of one.
All went well, done it quite a few times before. Changed gaskets and fuel injector o rings.
Test started it ran fine. Got to operating temp and quadruple checked all water etc. No leaks no fuss.
Turned it over to gas and ran as expected. No leaks and everything is running as normal.
Gave it quite a few good revs checking things and what not. A good 15 minutes running in my shed.
Perfect so time to take for a test drive.

The problem i had after it.

*Happens on both gas and petrol.
Drove about 500 metres down the road, car doing about 3k revs when it dropped to idle. No matter how much pedal it would stay at idle.
Let it slow down and notice i can drive between idle and around 1500 revs ok. Over that revs and it drops off to idle again.
Turned car off, restarted and gave it a rev. All good, went for a drive and the same thing happened. This happened 5 or 6 times.

What i have tried so far to fix the problem.

The obvious turning the car off fixes the problem until i drive it again.
While driving turning the car off, in neutral then starting and back into gear, it drives fine until symptoms come back again.
Tried taking the negative terminal off to let the ecu have a break. No change.
Tried swearing at it and as per damn usual that never helped.
Trying having a beer now and expect that to have no result.

What im guessing could be the problem.

The symptoms appear to be electrical in nature.
I have heard there is a sensor on the gearbox letting the ecu know its in gear, i wonder if this is playing up?
Some other sensor i have perhaps knocked or is not making a good connection? Fuel and water sensors i thought had a default setting in the event of a failure. The others i have no idea.

At this point im a little stumped to be honest.
Any ideas appreciated.

Andrew.

[rangieman]

Is it happening on petrol or gas or both ?
If it is gas id suggest check to see if your gas converter is freezing up due to a coolant air lock maybe [bigwhistle]

[DAMINK]

Is it happening on petrol or gas or both ?
If it is gas id suggest check to see if your gas converter is freezing up due to a coolant air lock maybe [bigwhistle]


Sorry mate should have stated that.
It happens on both gas and petrol. The converter is not freezing, i checked that. 100% sure.

Just had a shower. (do my best thinking in the shower)
Thinking now it is a really strong possibility its the TPS. If the TPS fails to read my throttle the ecu will go to idle yea?
Its not cutting out like if spark was lost, rather like the accelerator cable snapped.

Yea really thinking the connection to the TPS was not made properly and its briefly throwing an error and causing it.

[PhilipA]

No a 14CUX will run fine without a tps, but not have injector cutoff at 1500 rpm, and may not be as crisp in acceleration as is only using the MAF to sense load.
i should qualify as mine also had O2 sensors.

regards Philip A

[DAMINK]

No a 14CUX will run fine without a tps, but not have injector cutoff at 1500 rpm, and may not be as crisp in acceleration as is only using the MAF to sense load.
i should qualify as mine also had O2 sensors.

regards Philip A


Damn rules the easy one out.

[PhilipA]

Do you have any time delay relays in the system like to change from petrol to gas..?

also I didn’t get about the stepper. AFAIR they have 1 vacuum tap for the fuel pressure regulator. Is the other tap for gas.
gas diagnosis is always hard as the setups vary.
regards Philip A

[DAMINK]

Do you have any time delay relays in the system like to change from petrol to gas..?

also I didn’t get about the stepper. AFAIR they have 1 vacuum tap for the fuel pressure regulator. Is the other tap for gas.
gas diagnosis is always hard as the setups vary.
regards Philip A

There is a temperature delay for gas. Has a sensor on the gas rail.

Yes the stepper housing i put on has a second tap for the gas basically.
Hmmm i wonder if i piped that wrong some how?

I ran one pipe split in 2. One to the fuel regulator and one to the heater thing.
I ran a second pipe split in 2. One to the gas diafram and the other to the gas box thingamebob.
There is a box on the firewall for gas. It has a hose from the gas rail that goes to the box and vaccum also and an electrical connection. Its not a solinoid rather a square box of sorts.

143029 Added a pic of that box. Sorry its not a better picture. Its dark outside, windy and raining quite a bit so it tested my camera abilities.
The left V is where i have the vacuum and the Gas one is off the gas rail. Third thing is the electrical plug. Hard to see in this pic.

[LRJim]

Try unplugging the VSS and go for a drive and see what it does. Its what mine was doing, unplugged the VSS and drove fine. I thought my VSS was stuffed then I adjusted the TPS, plugged VSS back in and all good possibly a coincidence though. I know u said you ruled your TPS out but it might put you on the right path. Like you said you've installed the LPG many of times it's probably something else just to **** you!

Cheers Jim

[DAMINK]

Just hunting the web for ideas and come across this.

Engine cuts out around 1800 RPM, then resumes at 1500 RPM (https://www.rangerovers.net/forum/8-range-rover-classic/35127-engine-cuts-out-around-1800-rpm-then-resumes-1500-rpm.html)

Seems in this case most likely it was the TPS that caused it.


I had a couple recent PMs by people wondering if/how I fixed this problem... I ended up replacing the Throttle Position Sensor (TPS), Ignition Coil, Distributor Cap, and Alternator (in that order), since it turns out I had more than one gremlin last fall.

If I recall correctly, the TPS fixed the surging problem.... I think it was about $300, and the only test to see if it's the problem is to swap in a known-good TPS.

[LRJim]

Just hunting the web for ideas and come across this.

Engine cuts out around 1800 RPM, then resumes at 1500 RPM (https://www.rangerovers.net/forum/8-range-rover-classic/35127-engine-cuts-out-around-1800-rpm-then-resumes-1500-rpm.html)

Seems in this case most likely it was the TPS that caused it.



I think that's what I read at work when I first had the problem, I saw the words speed sensor and went for it. It drove fine afterwards just no speedo and cruise. I think it does something to the MAF or TPS but I'm not 100% sure about that.

Edit, after slotting the TPS and adjusting it it come good.

[bee utey]

I replaced a dodgy TPS on a late D1 a few months ago, it had very similar symptoms. In that case it has a simple LPG mixer system that continued to work normally. With injected LPG it's going to follow the petrol fault. IMHO D1's are too primitive to make good use of LPG injection, but that's another matter. If you have a good TPS just swap it. New ones are seriously expensive, used ones appear on ebay occasionally.

[LRJim]

I replaced a dodgy TPS on a late D1 a few months ago, it had very similar symptoms. In that case it has a simple LPG mixer system that continued to work normally. With injected LPG it's going to follow the petrol fault. IMHO D1's are too primitive to make good use of LPG injection, but that's another matter. If you have a good TPS just swap it. New ones are seriously expensive, used ones appear on ebay occasionally.Without hijacking the thread just out of curiosity what's a decent mixer for a 3.9? I have 3 lpg setups on 3 different cars that I don't use. 3.5? rodeo efi, xf 4.1 carb and the one off the 186 in the series. I wasn't thinking of going down the LPG route but I have all the gear and tanks to do so, any of this worth putting in there all impco ones.

Cheers jim

[bee utey]

Without hijacking the thread just out of curiosity what's a decent mixer for a 3.9? I have 3 lpg setups on 3 different cars that I don't use. 3.5? rodeo efi, xf 4.1 carb and the one off the 186 in the series. I wasn't thinking of going down the LPG route but I have all the gear and tanks to do so, any of this worth putting in there all impco ones.

Cheers jim

Impco (aka "the Boston Strangler") has no place in my LPG repertoire. Just about anything European gives better torque.

[theelms66]

My experience with injected gas .the wiring loom to the injectors (petrol) needed to be cut and the lpg wiring loom spliced in so the lpg computer would receiv a signal from the original ecu and use it to control the gas injectors. Could there be a connection issue in this area.

[DAMINK]

I replaced a dodgy TPS on a late D1 a few months ago, it had very similar symptoms. In that case it has a simple LPG mixer system that continued to work normally. With injected LPG it's going to follow the petrol fault. IMHO D1's are too primitive to make good use of LPG injection, but that's another matter. If you have a good TPS just swap it. New ones are seriously expensive, used ones appear on ebay occasionally.


Thankyou Bee Utey. Yes i have 2 spares so will try swap them out today.

[DAMINK]

Ok i can confirm its fixed.

Went out and connected roverguage and got this in the errors.

143056

Checked the connection to the TPS and sure enough it was not connected properly.
Reconnected correctly and then cleared the codes using roverguage.

Went for a drive and ran as expected.

Thankyou for your assistance guys.

[LRJim]

Ok i can confirm its fixed.

Went out and connected roverguage and got this in the errors.

143056

Checked the connection to the TPS and sure enough it was not connected properly.
Reconnected correctly and then cleared the codes using roverguage.

Went for a drive and ran as expected.

Thankyou for your assistance guys.Don't you just love it when its something simple! Lucky you didn't start pulling it all apart!

Cheers Jim