random rev limit @ 2ooorpm???

[ecxt4sy]

I just bought a 90 eclipse, 4g37 with 5 speed... after i run the car for a while it goes into "fail-safe?" and wont rev past 2000 rpms.. the problem isnt consistent, it does it every day although not every time i drive it.. it runs fine when i start it up in the morning and drives strong until about an hour after driving... ive unplugged the throttle position sensor which didnt do anything except give me a check engine light after it was unplugged.. i also unplugged the mass airflow sensor which kills the engine completely.. it has to be something electrical because the motor runs too good to be mechanical.. im stumped on this one .. any ideas?

 

[1995gsx20g]

does the car smoke when it hits this "2k rev limit" ?

 

[ecxt4sy]

no, doesn't smoke at all, even if i red line it.. doesn't even knock.. idles perfectly at 900 rpms.. i can tell when it acts up because it will idle at 1100 rpms..

 

[XiKeiyaZI]

Sounds like an ECU issue.

Pull it, check for leaky caps.

 

[ecxt4sy]

i pulled the ecu and it seems clean, no burn spots or anything resembling leaking caps.. can you still pull codes from the ecu even though it's under a 96?

 

[Boomdeeze]

Check the knock sensor, found out my knock sensor is shot and I have the same symptoms as you. Seems like there is a rev limit at about 2k.

 

[1995gsx20g]

well, no smoke present means its not the ignition system.

does the idle hunt?

+1 it could be the knock sensor

it would really help if you had some sort of logging tool so we can see what's up while its happening.

have you checked for vacuum leaks?

 

[ecxt4sy]

Ive pulled a couple of the vacuum hoses while the car was idling and they seem to be fine. they were my first guess because it is 20 years old and all the bushings are dry rotted but the vacuum hose and the ignition system are relatively new.. it does knock for a minute in the morning until i run the car down the road and then the knocking stops after i warm the car up, but i thought that was normal wear and tear on the valves..

it idles perfectly when its warmed up.. when i first start the car itll idle around 5-600 rpms until it warms up then it stays at 900 rpms. when it acts up and the 2k rev limit kicks in itll idle at 1100.. i know the o2 sensor is because it burns off too much gas.. im sure that it has to be something electrical because the engine itself is mechanically sound.. ive just never had this problem with any car in the past...

my car doesnt have a knock sensor.. i have the 4g37, im pretty sure that only the 2.0 turbos were the only ones that had them

 

[1995gsx20g]

im gonna assume when you say knock you mean lifter tick but yea lifter tick is normal at start up on older dsms.

when the car is dead cold it should be idling above 1200rpm at least. if not i would suspect the fiav in the throttle body( the wax chamber that makes the car idle high when cold)

if your car gets very poor gas mileage it very well could be caused by a vacuum leak so i would check that the same way as a BLT except i would not go over 1psi because the throttle body seals are flipped(in an nt throttle body) and will leak with any pressure.

your correct i totally forgot 1gnt's don't come with knock sensors so i guess you can rule that out

try searching "hunting idle", if your tps is acting up the ecu may be doing this because it sees no tps input and thinks the idle is trying to surge.

also check to see if the closed throttle switch is working properly.

 

[ecxt4sy]

i assumed it was the TPS also.. although the car runs the same without it plugged in.. i pulled it off the throttle body to check for oil because my pcv valve went bad and let a large amount of oil into the air intake tube, maybe a quarter of a quart.. i used an entire can of maf cleaner on the MAF and cleaned all the oil out of the tube and the throttle body without actually taking the the throttle body off because i dont have a replacement gasket for it.. when the car first acted up i beat the top of the throttle body with my tire iron (a little redneck, i know.. but i was pissed) and it worked fine for a few minutes then went back to the 2k rev limit.. any links for the entire throttle assembly? and the TPS should read zero volts, right?

 

[1995gsx20g]

zero volts isn't correct.
take a look at this thread - http://www.dsmtuners.com/forums/tuning-engine-management/241449-tps-reading-idle.html

take a look on VFAQ Site - Visual Frequently Answered Questions the tps is in the intake section

 

[ecxt4sy]

i didn't think that was right.. probably explains why the car runs the same with it unplugged.. is it possible the oil i had in the throttle body and air intake tube got into the vac system and is throwing the IAC off?

 

[1995gsx20g]

it is possible to clog up the iac port but that issue has no chance of keeping your car under 2k rpm.

 

[ecxt4sy]

well... I still have a problem.. I got a EGR block off plate from a stock 1.8 at the local junk yard, installed it and removed the EGR and lines which where dry rotted.. no other vacuum leaks.. I checked for ecu codes by ways of haynes manual.. i got 10 pulses or 1 long pulse.. i replaced the ecu which had leaking caps, also replaced the o2 sensor which was bad.. im still getting a CEL but is intermittent and when the CEL comes on the car bogs down like you let off the gas petal even if you have it pressed to the floor.. this Cell only comes on for a split second before going back off.. the car only bogs down when the CEL comes one... im thinking its my IAC because it is a 90 with the different throttle body sensors.. i have a throttle body from a 92 and the IAC on it has five wires compared to the four on my car.. I know it can be wired into the ecu because the ecu is also from a 92.. just not sure about which wire goes to which coil, plus the fifth wire goes??? i could be wrong with assuming its the IAC but i would like to bypass it all together... plus the lifters tick.. and then the tick goes away only to come back and repeat the same process of ticking and not ticking over several seconds... im still stumped.. please help?

had to edit because i failed to mention that the car idles at 600 rpms at start up when the engine is cold.. but idles fine after its warmed up and idles at 800 rps.. thats why i think its the IAC.. i dont want to spend the money replacing it when i plan on putting a new to me 2.0 this winter.. is it possible to bypass the IAC? also, i dont get any codes when i check the ecu.. my LED only lights up when the CEL comes on... the CEL wont stay on long enough for me the determine how many "blinks" to find out whats throwing the cars' ecu for a loop