D#m Sc400 !

[BangEmBoy]

Here I go with another good one lol ..... I recently puchased another Lex, this time a 1994 SC400 . When I first got the car, it drove fine . Then about a month ago, the check engine light came on . The DTC's # 25 & #28 indicated that it was running lean and that I have an 02 sensor problem ....Fast forward two(2) weeks, car is running fine, I go to the station and fill it up with gas; when I try to start it, it just turns over . I check everything and find out that I am not getting any spark . I pull the connection plug off of the right side coil to check for current . I had power, I check the other coil and had power there as well . So plugged the coils back in and the car started . It idled for about 2 mins and died . I had the car towed home, the next morning the car cranked up and ran just fine; for about 2 day's, and then did the same thing . I tried to retrieved some DTC's to help me fix the problem, but the check engine light wouldn't blink; and that's when I was given a clue . Whenever I tried to crank the the car, if the light would come on with the key, the car would run; but if it didn't come on, it wouldn't crank . I also noticed that when the light did come on, it would be weak, sorta flashing like it wasn't getting enough power ....That led me to checking my fuses and connection's . When I got to the underhood fuse box, I noticed that the fuel pump relay was warm, so I checked the circuit and found out the turn on wire was only getting about 4 volts . I ran a wire (ignition switched controlled) to supply 12 volts to the relay when the key was on . The car ran fine for two days, then did the no check engine light thing and wouldn't start .....Thinking that it was the ECM (since I couldn't go into diagnostic mode), I had the ECM rebuilt . When I got it back, the car craked up and ran just fine, but it idled erratcally . The RPM's would go up and down, from 1500 to 1000 . Other than that it drove fine with plenty of power . Then I noticed that sometime my RPM gauge and my MPH gauge wouldn't be working, then all of a sudden they would start to working again . I figured that the ECM must not have been built right, so I got another one, and I still have the same problem's; and now on top of that, my transmission isn't locking up . No let me rephase that, it is locking up, and then unlocking when driving . When driving at a steady rate of speed, you can feel it going in and out of lock up .... So far I have put in a new ECM, and a new fuel pump . I would really appreciate any help, feedback and guidance concerning this . I want to thank everyone in advance for your suggestions .

[SRK]

The poor hot start, uneven idling, and O2 sensors reporting lean makes me think you've got an intake air leak. Something may not be right between the mass meter and the throttle valve, or even downstream of the throttle valve.

It's worth considering that the O2 sensor may not be at fault, but reporting a fault - lean mixture. It's seeing excess oxygen, and that's interpreted as a lack of fuel to consume it.

The trans may be hunting because the throttle is being held at a different angle to compensate for the lean condition - the trans shifting is controlled by many factors and probably throttle angle is one of them.

Chances are good it's one thing, causing a lot of other problems, and finding the root cause is the goal, which then corrects everything else.

Good luck!

[BangEmBoy]

Thank you very much for your feedback and assistance SRK . I will definitely look into your suggestion ....

I did putter around with it today, just got in as a matter of fact; I had been advised that the MAF, the TPS and the fuel filter could be the cause of my problems, so I switched the MAF, and the TPS from my running LS . Needless to say; they didn't cure my problem, as a matter of fact, I now got a new code # 31 after the switch lol . I will be switching the parts back, and starting over with your advice on the morrow . Once again, thanks for your advice and help .

[fsuguy]

Hi,

If I am reading you post correctly, sometimes the engine does not even crank when you turn the key - does this mean it does not turn over, or it turns over but does not start (?) I would suggest you start at the battery and eliminate a bad connection first. Often, these terminals are hidden under covers and the acid destroys much of the connector, limiting or cutting off the current altogether. If the terminal/connector shows a lot of corrosion, you may want to consider a new connector. I had run into a similar issue and while the engine turned over, would not start. Once I replaced the connector ($20), it was like a different beast... surprised the heck out of me!

If it is not the battery terminal, then check the wiring, including ground wires - look for green in and around the wires and connections to the body - it sure sounds like an electrical problem to me, although it may also be what SRK suggests. My inclination is toward an intermittent electrical connection indicated by the on/off behavior of the gauges, the sometimes start, sometimes not, etc.

Let us know what you find, and good luck!

[Daniel091]

doesn't this model have a separate control module for the fuel pump?