Engine will sometimes not rev

Rotary91 · 07-09-2010, 01:27 PM

So I got this annoying problem, it does't happen often but it's annoying. Sometimes when I start the car (91 FC) it doesn't want to rev past 2k

, just bounces off the 2k mark. It isn't temp related because it happened with cold and engine and warmed up engine. Any help would be appreciated.

dudemaaan · 07-09-2010, 02:18 PM

how is the idle when this happens? does it change? idle lower, lumpier etc?

Rotary91 · 07-09-2010, 02:25 PM

I didn't pay much attention to idle when it happened, but I believe it was normal since the engine didn't want to stall

djmtsu · 07-09-2010, 02:27 PM

Any Check Engine Light?

If so, what are the codes?

If no CEL, when was the last time you changed the fuel filter?

Rotary91 · 07-09-2010, 02:33 PM

The check engine light is never on, and even if I check codes by grounding the test connector it doesn't say anything. I didn't get a chance to change the filter yet since I had the car for not even 2 weeks. If the filter was bad wouldn't the problem occur every time, or it gets clogged and then unclogged by itself?

Pete_89T2 · 07-09-2010, 05:48 PM

Quote:

Originally Posted by Rotary91

The check engine light is never on, and even if I check codes by grounding the test connector it doesn't say anything. I didn't get a chance to change the filter yet since I had the car for not even 2 weeks. If the filter was bad wouldn't the problem occur every time, or it gets clogged and then unclogged by itself?

Does your CEL come on for a few seconds with all the other idiot lights during the self-test before you start up? If not, the bulb might be bad or missing - suggest checking that first, fix as necessary and re-checking the error codes.

Rotary91 · 07-09-2010, 09:17 PM

Quote:

Originally Posted by Pete_89T2

Does your CEL come on for a few seconds with all the other idiot lights during the self-test before you start up? If not, the bulb might be bad or missing - suggest checking that first, fix as necessary and re-checking the error codes.

The CEL does come one during self-test, than disappears and never blinks to throw a code

NoDOHC · 07-09-2010, 09:54 PM

Does shutting the car off and the restarting fix the problem? If so, maybe ECU related (NO CEL, but still in limp mode). If not, how does it hit 2,000 rpm? Does it rev fast to 2000 and then just bounce, or does it rev slowly? Does throttle position have any bearing on it?

Rotary91 · 07-09-2010, 09:58 PM

Quote:

Originally Posted by NoDOHC

Does shutting the car off and the restarting fix the problem? If so, maybe ECU related (NO CEL, but still in limp mode). If not, how does it hit 2,000 rpm? Does it rev fast to 2000 and then just bounce, or does it rev slowly? Does throttle position have any bearing on it?

Shutting the car off is the way I always "fix" it. It does rev slow and rough/bumpy till it bounces at 2k. If I give it throttle where it would normally rev to 5k it still bounces off.

NoDOHC · 07-09-2010, 10:01 PM

I have to think that it is an ECU limp mode thing. I don't understand why the CEL is not getting set. It may be something with the position feedback from the OMP (that is the usual culprit).

Try unplugging the IAT sensor while the engine is running and see if the CEL comes on. I am pretty sure that it should.

Rotary91 · 07-09-2010, 10:12 PM

I will try it, also want to drive around wait for it to happen and do the self-test while its happening since every time it happens I'm not close to my house and don't have a spare wire.

Rotary91 · 07-11-2010, 08:41 PM

Still didn't get a chance to check the codes, hopefully my car will break down soon

Rotary#10 · 07-12-2010, 12:57 AM

Quote:

Originally Posted by Rotary91

Still didn't get a chance to check the codes, hopefully my car will break down soon

LOL try unplugging the AFM plug to see if the stays running with it unplugged. And your engine light should come on.

NoDOHC · 07-12-2010, 09:34 PM

Quote:

Originally Posted by Rotary#10

LOL try unplugging the AFM plug to see if the stays running with it unplugged. And your engine light should come on.

Wouldn't that disable his fuel pump?

That is why I always do the Intake Air temp sensor, it is easy to unplug and doesn't cause any major harm to run without it. (You have to have a warm engine).

You can unplug the TPS too (I just tried it, it will throw a code too).

Pete_89T2 · 07-13-2010, 07:07 AM

I'm thinking the OP is having wiring harness issues. Corrosion and heat exposure after 20+ years can cause intermittent opens/shorts in your wiring, causing all kinds of problems.

07-09-2010, 02:18 PM	#2
dudemaaan Rotary Fanatic Join Date: Mar 2008 Location: Brenham, TX iTrader: (4) Posts: 335 Rep Power: 17	how is the idle when this happens? does it change? idle lower, lumpier etc? __________________ 500+ HP thanks to: Fast reacting IAT sensor thread! Mechanical Pre-turbo Water Injection Thread Dual Stock fuel pumps Thread T2 differential swap!

07-09-2010, 02:25 PM	#3
Rotary91 Rotary Fan in Training Join Date: Jul 2010 iTrader: (0) Posts: 36 Rep Power: 0	I didn't pay much attention to idle when it happened, but I believe it was normal since the engine didn't want to stall __________________ '91 FC3s

07-09-2010, 02:27 PM	#4
djmtsu My minds tellin' me no... Join Date: Feb 2008 Location: Murfreesboro, TN iTrader: (10) Posts: 4,043 Rep Power: 21	Any Check Engine Light? If so, what are the codes? If no CEL, when was the last time you changed the fuel filter? __________________ 1976 Mazda Cosmo RX-5 1976 Mazda Cosmo RX-5 2003 Toyota Tundra TRD 2015 Toyota 4Runner SR5

07-09-2010, 02:33 PM	#5
Rotary91 Rotary Fan in Training Join Date: Jul 2010 iTrader: (0) Posts: 36 Rep Power: 0	The check engine light is never on, and even if I check codes by grounding the test connector it doesn't say anything. I didn't get a chance to change the filter yet since I had the car for not even 2 weeks. If the filter was bad wouldn't the problem occur every time, or it gets clogged and then unclogged by itself? __________________ '91 FC3s

07-09-2010, 09:54 PM	#8
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin iTrader: (1) Posts: 855 Rep Power: 17	Does shutting the car off and the restarting fix the problem? If so, maybe ECU related (NO CEL, but still in limp mode). If not, how does it hit 2,000 rpm? Does it rev fast to 2000 and then just bounce, or does it rev slowly? Does throttle position have any bearing on it? __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)

07-09-2010, 01:27 PM	#1
Rotary91 Rotary Fan in Training Join Date: Jul 2010 iTrader: (0) Posts: 36 Rep Power: 0	Engine will sometimes not rev So I got this annoying problem, it does't happen often but it's annoying. Sometimes when I start the car (91 FC) it doesn't want to rev past 2k , just bounces off the 2k mark. It isn't temp related because it happened with cold and engine and warmed up engine. Any help would be appreciated. __________________ '91 FC3s

07-09-2010, 10:01 PM	#10
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin iTrader: (1) Posts: 855 Rep Power: 17	I have to think that it is an ECU limp mode thing. I don't understand why the CEL is not getting set. It may be something with the position feedback from the OMP (that is the usual culprit). Try unplugging the IAT sensor while the engine is running and see if the CEL comes on. I am pretty sure that it should. __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)

07-09-2010, 10:12 PM	#11
Rotary91 Rotary Fan in Training Join Date: Jul 2010 iTrader: (0) Posts: 36 Rep Power: 0	I will try it, also want to drive around wait for it to happen and do the self-test while its happening since every time it happens I'm not close to my house and don't have a spare wire. __________________ '91 FC3s

07-11-2010, 08:41 PM	#12
Rotary91 Rotary Fan in Training Join Date: Jul 2010 iTrader: (0) Posts: 36 Rep Power: 0	Still didn't get a chance to check the codes, hopefully my car will break down soon __________________ '91 FC3s

07-13-2010, 07:07 AM	#15
Pete_89T2 Lifetime Rotorhead Join Date: Apr 2010 Location: Elkton, MD iTrader: (1) Posts: 874 Rep Power: 15	I'm thinking the OP is having wiring harness issues. Corrosion and heat exposure after 20+ years can cause intermittent opens/shorts in your wiring, causing all kinds of problems.