low rpm engine jerkiness
Thread Starter
Junior Member
Joined: Oct 2017
Posts: 29
Likes: 0
From: Kiev
low rpm engine jerkiness
Hello, I'm working on RX7 "89 and have a problem with low RPMs about 1.5 - 2k. The engine works very unstable in that range, when moving car jerks like crazy. It feels like some automatic control tries to add more throttle periodically.
https://youtu.be/SE3Q1DpAfLc
(at 0:14)
I found that uncalibrated TPS may cause similar problems and tried to calibrate it:
warm up engine
turn off
disconnect TPS
measure resistance range and tune it to 0.9 - 1.0 ohm on idle throttle position
It helped, but.. After some time when cold launching the engine begin to rev at 3k RPM. I measured the TPS resistance on cold engine and it was more than 1.5. Seems the TPS readings very dependent on temp and should have two settings for cold start and warmed operation.
Also the manual says there should be 2 sensors (narrow range / full range) but my RX for some reason only has only 1 sensor with 3 pin connector. ( https://gyazo.com/3aa28f85f8a4abe0f6ea0a738ec483f5 )
Any ideas about that?
https://youtu.be/SE3Q1DpAfLc
(at 0:14)
I found that uncalibrated TPS may cause similar problems and tried to calibrate it:
warm up engine
turn off
disconnect TPS
measure resistance range and tune it to 0.9 - 1.0 ohm on idle throttle position
It helped, but.. After some time when cold launching the engine begin to rev at 3k RPM. I measured the TPS resistance on cold engine and it was more than 1.5. Seems the TPS readings very dependent on temp and should have two settings for cold start and warmed operation.
Also the manual says there should be 2 sensors (narrow range / full range) but my RX for some reason only has only 1 sensor with 3 pin connector. ( https://gyazo.com/3aa28f85f8a4abe0f6ea0a738ec483f5 )
Any ideas about that?
Rotary Freak
Joined: Nov 2001
Posts: 1,530
Likes: 234
From: Alexandria, VA
The 89-91 RX7 uses 2 sensors (narrow range / full range). One of the two sensors controls the electronic OMP. The 86-88 RX7 uses one sensor since they have manual OMP controlled by the throttle linkage. These cars have a tendency to buck when driving at low speeds especially when too high gear is selected. This can be minimized by proper adjustment of TPS sensor, Also, check the health of you charging system (i.e., connection at battery terminals, alternator, etc.). I once had a bad alternator that would often cause bucking at low speeds. Apparently, these cars become finicky if the ECU is not getting the proper supply voltage. Also, check your ignition timing and idle speed.
Thread Starter
Junior Member
Joined: Oct 2017
Posts: 29
Likes: 0
From: Kiev
Ok, something got very wrong after a day from TPS calibration, not sure it's connected but now the car only cranks and not starting. The fuel pump works (checked near fuel filter) but no fuel inside sections, the spark plugs are dry. Will check other things..
