Hi guys, i have a 1990 GTU and as the title states, my 7 is having some issues reving past 6.5k. I just got this car in a trade a few days ago for my 95 mx6 because i've wanted one since i could legally drive so i was willing to look past that problem when i got it. Supposedly the engine was rebuilt a while back, but we don't know when it was rebuilt. everything else on the car seems to run fine except for the clutch slipping, but that's being taken care of very soon. It doesn't feel like its loosing power around 3800 which i from what ive read is a common failure for the FC. MY guess was that this might be fuel related, but since this is my first RX, i figured i might get some advice from you guys before i start replacing everything that wont fix the problem. Ive searched the past few days under different topics, but nothing really stands out as being similar to my problem, but maybe i'm just not looking in all the right places.

If anyone has any suggestions to throw at me i would very much appreciate your help

 

first change the plugs.

 

Can it not go past 6500RPM at all under load (as opposed to free revving)? If it can't, it's probably your TPS and it would need replacing.

 

Could be TPS, vac leak or the 5th and 6th ports not functioning properly. Search for "TPS adjustment", buy a multimeter and check the voltage or resistance. Look for any cracked/disconnected vacuum lines and move the 5th and 6th actuators up and down by hand to make sure they aren't seized.

 

VDI/Aux ports have nothing to do with backfiring and hesitation.

Check resistance between your injector connectors and the ecu and the battery when the ignition is on. Well, the 12V terminal to the battery, and the ground wire to the ecu plug. On all 4 injectors.

Make sure your afm moves freely and, that the fuel pump is good.

This is assuming you already have a good fuel filter, plugs and wires.

You may also want to test your ignition coils.

 

ill see about testing the TPS within the next couple days because thats kinda what i was leaning to at first, ill also check to see if it will free rev all the way tomorrow. new plugs wouldn't hurt either, i might just buy those and a fuel filter tomorrow if i have time. ill just try and get the basic tuneup done and see where that leads me.

i don't remember seeing/hearing any vacuum leaks last time i was checking under the hood, so i think ill be searching for some electrical gremlins tomorrow. thx guys

 

still at work, but i had to run an errand earlier so i decided to free-rev it since i wasn't waking anyone up like i would have been this morning lol. well it still hesitates a bit but it goes up all the way. and i saw smoke when i reved it up all the way, lots of it. Im starting to think someone might have been lied to somewhere down the line. the guy i traded cars with had just bought the car but was previously bugging me about buying my mx6 so then we traded when he bought the RX. he said the guy told him it was rebuilt not too long ago, but like i said, im starting to doubt that is the whole truth behind this car. well if i can get the spark plugs and wires tonight, ill end up changing them and checking the TPS tonight.

 

Even if it was rebuilt that doesn't mean it was done right or broken in properly. Don't assume too much, used cars are always a gamble, especially these.

 

yea, im willing to roll with the punches on this gamble. I acctually know a friend of a friend who has an already street ported 13b and a PP 13b just sitting in his garage. i might just start saving up and buy the street ported motor sometime in the not to distant future, it would be cheaper than buying a rebuild kit if this motor is up to par. but thats further down the road. i got the spark plugs a little while ago and a new fuel filter as well, the wires will be in on monday. thanks again for all your help guys. ill keep this updated as i do the tune up

 

update:

I changed out the sparkplugs and wires and just got done adjusting the TPS using the led method. when i plugged my rigged up lights in there both lit up so i adjusted the screw counter clockwise til one went away then took her for a spin. well now she gets past 6500 but seems to die out on the top end, im thinking it might have something to do with the ports being stuck closed possibly? The guy i traded cars with said he was thinking that too since the actuator near the bottom of the lower manifold seem stuck and its just really hard to get anything down there to pry on the arms to see if they will budge. do you guys have any more suggestions?

 

If it smokes some on startup & free reving it high, but not after it's been running for a bit, that's normal.

Also, if it feels like the top end is weak, you should definitely check the activation of the aux ports and VDI. On an S5 this is really easy since they're operated by the air pump. Just stand where you can see the valves & open the throttle. If they're not working, you won't see any movement. Connect a tach or have someone help if you want to know that they're opening at the right rpms (3.8k & 5.2k)

 

had some time to play around with it some more yesterday. I came to find out that the 6pi ports were indeed stuck and i wasn't able to get them unstuck. Also i advanced the timing just a bit above where it was and it helped the car get past 7000 a bit easier. Now i just need to get in there and pull out the parts that are stuck and get her breathing in the 8000rpm range again.

 

bringing back an old topic with new info

i think i may have found the actual culprit behind my problems. for the longest time i had a sneaking suspicion about my fuel pump being the cause of my woes so a while back i was taking out the fuel pump to change it with a stock one i found laying around the shop (it didn't work as i soon found out) and when i pulled it out i realized that the pump i had in there was not a stock pump at all but i more than likely a walbro but i just don't know for sure . all i know is that it isn't stock. i am also about to install a wideband i have from another project so i can see just how bad this problem really is and keep an eye on things. im trying not to drive the motor that hard because i don't know exactly how lean it is running. should i chance it and try to do a rewire since the walbro draws more amps or should i just try and find another stocker since im not planning on heavily modifying the RX for a while.