RPM hang up at 3400 - Defender Source
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  #1  
Old June 18th, 2011, 08:33 PM
jhhorse
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joe heins
1995 defender 90
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RPM hang up at 3400

I have searched and found this problem on this forum, but the threads never provide a conclusion:

Truck started popping CEL for o2 sensors both left and right (at different times) after long highway drive with hills, (new lambda sensors within 5k miles)

Even when it doesn't pop the codes, when going up hill or whenever under a load, RPM gets to about 33-3400 and the engine loses power, won't go higher on the rpm.

Engine revs normally when in neutral, no load. As long as no prolonged highway drives or no rpm above 3200, engine runs fine, starts up every time.

Assuming good fuel pressure and mostly new ignition parts, anyone know the fix (I have seen past threads with similar issues, but no resolution on the thread.)

Thanks
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  #2  
Old June 18th, 2011, 10:30 PM
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Jason England
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Air problem ... Loose air intake or vacuumn tubes collapsed ... That's always my guess if fuel and ignition is all good ...
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  #3  
Old June 19th, 2011, 01:39 AM
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Dave Sherwood
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Had a similar issue with a classic RR. There was a deadspot on the throttle pot.
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  #4  
Old June 19th, 2011, 10:23 AM
jhhorse
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joe heins
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Thanks, I have checked the TPS and swapped it with another, same result. I checked for a vacuum leak using carb leaner, did not find anything, lots of other threads with this similar problem on other forums, most of the time it was an air blockage of some type.
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  #5  
Old June 19th, 2011, 12:33 PM
jhhorse
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joe heins
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Ok so I disconnected the MAF and drove the car and this problem of flattening out at 3400 rpm is gone, motor revs up under load well abve 3400 rpm. Does this definitely point to a sensor and is there a voltage check I can do on the MAF or a cleaning procedure?
thanks
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  #6  
Old June 19th, 2011, 01:09 PM
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Phillip
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it doesnt seem like either of my trucks will start without the MAF connected, cleaning the MAF smoothed my trucks out a little.
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  #7  
Old June 20th, 2011, 08:23 PM
jhhorse
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joe heins
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I got a hold of a used MAF, will install and see what happens. took another look for vacuum leaks, seems tight.
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  #8  
Old June 20th, 2011, 08:52 PM
CDeWan
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Clay DeWan
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I was thinking that possibly your cats were clogged. Not sure if you put new ones on but could be an obstruction in the exhaust flow. don't think it would show at idle but maybe at speed or under load. I am nut sure how to check but if the gas is not exiting correctly I think it would end up eating up the O2 sensors due to heat.

------ Follow up post added June 20th, 2011 09:00 PM ------

O...just to add to the last point. In my stupidity, I once installed shorten flutes in the intake to flow more air into the cylinders. On an offroad trip, the glue holding in the flutes let go so some of the flutes were bouncing around in the intake blocking the cylinders from getting air thus leaning out the motor at RPMs this lead to engine failure. Not sure if you have ever check the 8 intake flutes to see if any are not where they should be.
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  #9  
Old June 20th, 2011, 09:40 PM
jhhorse
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joe heins
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Thanks Clay, I will take a look at the intake if this MAF doesn't make a difference. I will also find a way to check the cats, thanks again,
Joe
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  #10  
Old June 22nd, 2011, 07:13 PM
jhhorse
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joe heins
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CEL on no code!

Ok, while waiting for a MAF to arrive, I have been looking for possible air leaks, etc. Tried to drive today, starting to backfire in 1-3rd under a load, got a CEL with no code! Every sensor connected.

Anyone seen that before? Is this an ECU?

Thanks
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  #11  
Old June 22nd, 2011, 10:44 PM
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Jason England
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Unlikely to be an ECU ... although if you can access a spare swapping it over would remove any doubt.

'As air flows through the MAF Sensor and specifically over its wire elements, inevitably some dirt accumulates. Although the mileage between cleanings seems to vary widely, the MAF Sensor will need to be cleaned occasionally. It's possible to buy "MAF Sensor Cleaner" in a spray can. Regular old "electrical contact and tuner cleaner" will work too. If cleaning as part of routine maintenance, disassembly of the sensor body isn't generally required. '

http://www.britishv8.org/Articles/Rover-14CUX-EFI.htm
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  #12  
Old June 23rd, 2011, 12:16 PM
jhhorse
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joe heins
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I did clean the MAF, did not seem to improve it that much, Here is waht is going on now:

Yesterday while driving it started backfiring when low speed trying to accelerate,

and......speedometer stopped working,

So I disconnected speed transducer, no more backfiring and speedometer came back to life,

still hangs up at 3400 rpm under load and popped another 02 sensor code, smells like it is running rich,

another maf coming in today, will swap and see what happens.

thanks
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  #13  
Old June 23rd, 2011, 01:31 PM
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Jake K.
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Here's a silly one while you are waiting. Take the belt off the alt. and drive it down the street and see what happens. I've had the alt. do weird things over the years. Worth a try.
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  #14  
Old June 23rd, 2011, 02:51 PM
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James Pierce Jr.
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Quote:
Originally Posted by Roverchef View Post
Here's a silly one while you are waiting. Take the belt off the alt. and drive it down the street and see what happens. I've had the alt. do weird things over the years. Worth a try.
Definitely worth a try. Same thing happened to mine last August. At the time I also noticed the problem was worse when the AC and head lamps were on.

------ Follow up post added June 23rd, 2011 01:53 PM ------

Quote:
Originally Posted by leastonce View Post
Jason that was an excellent link. Lots of good information.
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  #15  
Old June 23rd, 2011, 03:05 PM
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Quote:
Originally Posted by jamespierce View Post
Jason that was an excellent link. Lots of good information.
Yeah seariously! Tempted to print that out in color to store away or in the car.

------ Follow up post added June 23rd, 2011 03:07 PM ------

Quote:
Originally Posted by Roverchef View Post
Here's a silly one while you are waiting. Take the belt off the alt. and drive it down the street and see what happens. I've had the alt. do weird things over the years. Worth a try.
x3. Alt did all sorts of weird crap on its way out. At least three things I thought I'd need to replace have now miraculously started working just fine after the alt replacement.
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  #16  
Old June 23rd, 2011, 05:27 PM
jhhorse
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joe heins
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I guess I better take a look at the alternator, different MAF, same result,

plugged the speed transducer back in and the speedometer stayed alive, so not sure what is happening there.
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  #17  
Old June 24th, 2011, 07:30 AM
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J. Michael McCaig
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I had close to the same symptoms with a RRC once. Idled fine but loss of power under load and limited RPM. I know folks say that ignition amplifiers just quit completely when they go bad but changing the one out on the RRC cured the problem.
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  #18  
Old June 24th, 2011, 08:48 AM
dchapman
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Daniel Chapman
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Kinda of the same symptoms on a 1995 D-90 I had here last month, although his speed-o was 100% dead anyway (cable). The truck would sometimes start, run, and drive fine; other times it would spit and sputter and backfire as soon as it started; and other times it would start and drive fine for 30-miles, then start spitting and sputtering like it was running on 4-cylinders. Sometimes you could pull over and re-start the engine and it would be fine, other times the truck would need to sit for a bit.

The problem ended up being the fuel pump.

FWIW, while the tank was out to fit the new pump, I had Tillery send me a Discovery fuel pump access plate and installed it for future use. I also installed one of Safari Rovers aluminum tank skids.
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  #19  
Old June 24th, 2011, 03:44 PM
jhhorse
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joe heins
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I think after driving with sensors on/off and up and down hills, here is what I have isolated:

With MAF disconnected, power is there, revs go up to at least 4k under load (I did not try higher)

With MAF hooked up, If I never rev the rpm above 3300 I can drive all day up and down hills and runs fine.

If I try to get above 3300 rpm under load, the engine bogs down, definitely getting too much fuel (or not enough Spark) you can smell the gas big time, then shortly after trying that high rpm for a couple of times, you get a CEL for 02 sensor.

My next focus is on the ignition amplifier or another part of the ignition system, possibly the alternator? as mentioned before.

thanks, if anyone has a miracle cure, please let me know!
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  #20  
Old June 24th, 2011, 06:25 PM
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James Pierce
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James Pierce Jr.
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Does it do it in closed loop or just after it has warmed up?
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