My son just bought a 1990 740 GL it has alot of issues but one of the main problems is it won't go over 50 mph and it doesn't shift unless you let off the accelerator.Even the rpms don't go very high.Any ideas what could be the reason behind this?

 

Not enough information. Try to describe exactly what you hear. When the car starts from stop count how many times it shifts. Does it shift 1st to 2nd to 3rd then to 4th and OD. What is the engine speed at 50 MPH. What happens when you floor the gas peddle. Does the motor not respond or does the transmission RPM go up. Have you checked the diag. codes to see if there is one . How does the engine sound. Just try to describe what is happening.

 

my son says it shifts 2 times and at 50mph the rpms are at 2000.I will have a better idea tomorrow when he comes by.I noticed the motor sputters when he first starts the car.He has done a tuneup,o2 sensor,and crank shaft pulley.He says diag.says something about the pcv valve.thanks for any help you can provide

 

50 @ 2000 rpms is about right. The overdrive for my '87 was in the rear axle, so that would make the final drop in rpm's. My '87 had a flame trap, has that been cleaned or replaced? That still should not stop the car from picking up more speed. Did he replace the cap and rotor when he did the plugs?

Oh, almost forgot. I had that problem once with my 960. I pumped some Valero gas in it that had ethonol in it and it would not go above about 48 mph until I got that gas burned down and put some more gas in. Maybe he has some bad gas. Have him put some Stabil in it and maybe some octane boost to see what happens.

 

[quote=rspi;300404]50 @ 2000 rpms is about right. The overdrive for my '87 was in the rear axle, so that would make the final drop in rpm's.


I've not heard of a rear transaxle in a 740. I assume you mean the OD unit on the transmission if it was a M-46 4 speed. If auto then the OD is in the transmission. I think 2000 rpm in OD is around 55mph.

 

Try this from a standing start. Just press on the accelerator in a normal fashion and you will feel it shift from 1st to 2nd to 3rd and then 4th (at this point you will feel another slight shift) When you go into 4th (OD) the torque converter locks up which gives you the extra slight shift. By the way the 4th (OD) usually shifts around 45 mph. So at 55mph your tach should read about 2000 rpm unless you have changed the tire size.
As to the sputter I don't understand what it is. I would first suggest fixing the code that came up in the diag. and see if it still sputters.