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Discussion Starter #1
I have an intermittent problem with my Nissan Altima '96 GXE 2.4L A/T 153K miles:

After driving for a few minutes, I loose power with the engine above 2000 RPM (exactly). Below 2000 RPM, engine / transmission behaves normal, even at speeds of 40MPH (under light load/low RPM). Attempting to increase RPM to above 2000, causes engine speed to oscillate at 2000 RPM (Freq=~2/sec). This occurs at any vehicle speed including park.

I believe it is some kind of engine control issue, since when I turn off the car and let it sit for 15 seconds, the problem dissappears. I have replaced the fuel filter to rule this out as a cause, but did not believe that this was the culprit due to the precise way this failure occurs, and the ability to return the car to normal operation with a simple 15 second rest.

The first 6 times this happened, MIL light did not turn on, and no OBD-II codes were registered.
This morning, the problem did not occur, but the "check engine" light turned on, and 3 OBD-II codes were recorded:
P1900 "Manufacurer Contrl. Transmission" (SIC)
P0733 "Gear 3 Ratio Incorrect"
P1900 "Manufacurer Contrl. Transmission" (SIC)

Looking at sites with OBD-II codes for Nissan, P1900 appears as "Cooling Fan", so this is somewhat confusing.

Extensive searching on the web has turned up no pointers other than possibly TSB: 97-028 :
MIL ON - DTC P0731,P0732,P0733 (A/T Signals) No Symptoms. (although I'd have to admit, I do have a few symptoms -- although not when the MIL came on). I'm not able to locate the full text of the TSB.

Any assistance would be greatly appreciated!
Thanks,
--Michael
 

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Biru O' Kudasai
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Replace the fuel filter and check the fuel pressure.

It sounds a little like the coolant temp sensor is malfunctioning which could cause the multiple P1900 codes and have something to do with the stalling.
Check the cooling fan low speed operation by turning on the A/C. If it doesn't turn on then the relay under the hood is possibly bad.
The P0733 code means the trans cannot be shifted into third. If it can be shifted into third then clear the code and if it comes back I will get more information or you could take it to your local Nissan dealer for help.
Check these and let me know what you find.

Troy
 

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Discussion Starter #3
Car overheated, now in shop

On the way home friday, the car overheated. Had the car towed to the nearest Altima dealer, and they diagnosed a cracked waterpump housing. After they completed the repairs, it still overheats, so they are looking into whether it may be related to the head gasket.
I'm thinking the RPM limit to 2000 was the controller's attempt to keep the engine from overheating further, although I am a bit confused as to why no PCM codes were reported for the first few times this happened, and temp gauge read normal.
Anyway, it sounds like this repair may be more than the car is worth...sigh -- it was a great car...
--Michael
 

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These cars have good quality engines. If it has always been taken good care of and driven carefully, I believe, there shouldn't be major issues that will cost you a fortune. It is not a secret that dealership always tries to do as much repairs as possible and their prices are high.
I suggest to check the easily repaired items first: fluids levels, drive belts, leaks - Inspect transmission fluid:must be pink color - not brown,not smell burned,not be foaming and correctly leveled. Simply look under the car and see if any fluid is drooping down. If not - still inspect the transmission and cooling systems visually,use mirror if needed (good idea to drive it a few miles before checking). See if both fans work - they must switch on and off periodically while engine is running. Check accelerator and shift cables for proper adjustment and smooth operating. Drive belts should be correctly centered. Overheating problems may also be caused by thermostat or water pump faulty, bad radiator cap.
Poor engine performance; improper adjustments; hydraulic, mechanical, computer-network malfunctions - they all can cause transaxle malfunction.
There is also a chance that your shift and cooling system problems are not related.
Any way transaxle system is sophisticated and if none of before mentioned helps, you will need a specialist help.
Haynes Repair Manual will give you all necessary information and advices. Buy it in auto part store or online for about $15.
 

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Discussion Starter #5
All,
Thanks for your help. Here's the current status:
The engine runs, but *very* rough. There is steam in the exhaust, and 180ppm of hydrocarbons in the coolant, indicating a head gasket failure, possibly worse. The exhaust manifold is cracked. Steam escapes from the engine near the exhaust manifold. On the (very slow) 6 mile drive home I had to stop half way to allow the car to cool enough to see through the steam, although the engine temp registered only a bit over where it normally registers.

The dealer recommended a re-man engine which runs about $4K including labor (approx $930) -- that is, if I were to do anything at all.

I'm guessing that at a minimum this will require a new head gasket and head resurface (along with a new manifold). I'm thinking about possibly attempting to rebuild this myself as a project (I knew there was a reason I cleaned out the garage :).

So here are my questions:
1) Am I nuts?
2) I'm guessing that there won't be much material cost in tearing down the engine, and I'll decide whether or not to rebuild depending on the extent of the damage I find. What potential hidden problems should I be on the lookout for? It would be a bummer to repair the head, and get it all back together to find that there was some other problem lurking (like the shop did).
3) What diagnosics should I run while the engine still "works" to help me pin-point items which need replacing? (Compression values, anything else?)
4) What special tools should I have on hand for this project?

I'll definitely get the Haynes repair manual and give it a thorough review before starting.
--Michael
 
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