I'm no longer interested in solving this issue. The swap, which was intended before this all happened, has already started.

I am only leaving this info up to help others who might search for it.

1988 CRX HF. Stock engine, '88 Si transmission, 171k miles. Still OBD0.

Car bucks upon tip in and tip out of accelerator pedal. The problem seems to get worse as time goes on and the problem seems worse on a single ride once the car begins to warm up. It started as feeling like the hesitation some automatic transmissions feel, now it feels so violent it feels like the transmission is dropping (I had that happen to a stock HF tranny about two months ago).

If the CEL was on the car runs fine. If the CEL is off it would run poorly. If the TPS is unplugged the car runs fine (but gets 28mpg instead of 43mpg). The idle is smooth and even.

Troubleshooting Information:

Circuit Schematic: PGM-FI (Si and HF) (page 1)
Circuit Schematic: PGM-FI (Si and HF) (page 2)

Troubleshooting Flowchart: PGM-FI Control System (page 1)
Troubleshooting Flowchart: PGM-FI Control System (page 2)

Possibly related sensors that could have failed and be causing the issue (I need to test these):

Troubleshooting Flowchart: Exhaust Gas Recirculation System (page 1)
Troubleshooting Flowchart: Exhaust Gas Recirculation System (page 2)
Troubleshooting Flowchart: Exhaust Gas Recirculation System (page 3)
Troubleshooting Flowchart: Exhaust Gas Recirculation System (page 4)
Troubleshooting Flowchart: Exhaust Gas Recirculation System (page 5)

Troubleshooting Flowchart: PA Sensor (page 1)
Troubleshooting Flowchart: PA Sensor (page 1)

Action taken:

Read CEL code: 7 - THROTTLE ANGLE

Code has been cleared multiple times by pulling underhood ECU fuse.

Replaced TPS with Blox TPS. Within a week or so the problem was back in full force.

Checked TPS voltage. Results: .5v and 4.46v. (It's supposed to be .5v and 4.5v.)

Tested C7 (RED/BLU), C12 (GRN/WHT), and C13 (YEL/WHT) from the ECU to TPS. Tested from C210 white round connector on the passenger shock tower to ECU, from C210 to TPS, and from TPS to ECU. Everything checked out perfectly.

Swapped ECUs (PM8-H for PM8-A).

Replaced single-wire O2 sensor on manifold (only one this car has). This has rid us of the CEL, which is for the TPS (7) anyway.

Measured voltage from YEL/WHT (+) terminal to GRN/WHT (-) terminal. Read 4.94v (should read 5v).

Problem persists.

 

have you tried a known good working ECU just to check? I'm sure for the time being even a PM6 would work just to see if it throws the same code.

 

have you replaced the ground wires?

since you've replaced both items involved (ECU & TPS) it has to be something that changes or deteriorates with time.
warming of a bad connection (due to engine heat or power transfer) will cause the TPS reading to slowly offset itself. It offsets every sensor but the TPS is more sensitive.

can you datalog when the problem occurs to see what's going on?

 

The HF ECU has been difficult to find. I finally found one, but I'm still getting the same problem, of course.

I don't know anyone who would allow me to borrow a PM6. I don't think I even know anyone with a Civic/CRX Si.
The ground wires have been replaced

It's a stock HF and the PM8 has no EPROM available. So no, I can't datalog. This car isn't even set up for that.

 

A scope or a good GMM would be necessary in this case. You want to monitor the TPS signal and see if it drops out when the problem occurs. It is very possible that the problem is not the TPS at all. Stumbling or hesitation on tip-in sounds like an ignition problem. And you said the code is gone and has not returned? I do not want to send you on a wild goose chase, just opining.

 

The problem only happens when the car is in motion, so it is just about impossible for me to check this while the problem happens.

I can tell you that the tach doesn't move at all when it happens though. It's like the gauges don't even register there's a problem. It almost feels like the car's fuel supply has been totally cut off. No power at all for a second.

If I keep heavy on the accelerator it seems to not happen as much.

At this point I almost feel like it's all been a wild goose chase, so it's okay.

 

So I got this message today from a friend also curious of cause of the problem:

If you look at the links in the first post for the circuit schematic you'll see the reference voltage (7:YEL/WHT) appears to be linked with the EGR valve lift sensor and Atmospheric pressure sensor. I'd mentioned these to a friend before, but he didn't think it should have any or much effect on the TPS since it goes to the EGR first.

I suppose I can check it out, but I'm not really wanting to anymore replace parts to an engine I'll be selling soon and I won't be reusing those parts when I get the Y8 in (when it finally gets done!).

Just figured I'd update in case anyone else searches and finds this.

 

Perhaps I should point out if these two other parts were throwing codes related directly to them, they would be CEL 12 (EGR system: for Std. CAL:A/T and HF only) and CEL 13 (Atmospheric Pressure). Perhaps the TPS is a lot more sensitive though.

Applicable service manual pages. Meant to post these earlier, but had to leave in the middle of scanning them.

Troubleshooting Flowchart: Exhaust Gas Recirculation System (page 1)
Troubleshooting Flowchart: Exhaust Gas Recirculation System (page 2)
Troubleshooting Flowchart: Exhaust Gas Recirculation System (page 3)
Troubleshooting Flowchart: Exhaust Gas Recirculation System (page 4)
Troubleshooting Flowchart: Exhaust Gas Recirculation System (page 5)

Troubleshooting Flowchart: PA Sensor (page 1)
Troubleshooting Flowchart: PA Sensor (page 1)

 

Thanks for the help with this issue, anyone who helped me out.

It doesn't look like I'll be testing those other parts anytime soon since tonight we started disconnecting everything to start the engine swap. The EGR and baro won't be used.

Perhaps one day this might help others out though? Good luck to anyone else.

----

Also, I noticed I had forgotten, but I was able to smoothly the car up sitting in my driveway and the car would bog occasionally. Well, I pressed the pedal smoothly.

 

could be faulty MAP sensor!


this happened to me on my ef sedan with b18b recently.

try to get it dead on .5 -4.5

mine was .5 - 4.3 and i put it dead on and runs smooth

 

Thanks for the suggestion. The car has begun being swapped though, so this is behind me. I'm deleting the firewall-mounted MAP sensor.

 

I deleted all the bs on the firewall map hoses,brackets etc...
GRabbed a self tapping screw into firewall so its just the sensor and a hose to the back of my manifold.

If you decide to do this make sure it is above the manifold!

 

I'm swapping in a Y8 and the MAP is on the throttle body.

 

Yea it is on everyother motor except ef with dpfi!

Just didnt have one my self so i reused and i think it performs better than my throttle one!? thats just MO

 

This is an engine I had in another car and have owned since 2002. It's always driven great. It's going into this CRX basically the same way, but will be OBD1 yet running on a Y8 map.

I don't want to go too far off topic in this thread though, in case anyone needs it for help later. I don't want anything in here to confuse the topic at hand. Thanks.

 

I would test voltage at the ecu going to the pa sensor. See if there's 5v. Coming from the ecu to the sensor tghat 4,94 volts may be the problem.

 

Also have you tested the voltage as it drops from the tps sensor see if there's a jump in voltage in thed first 10 volts going to the input of the ecu.
And test the resistance across your ignition coil

 

I'm no longer interested in solving this issue. The swap, which was intended before this all happened, has already started.

 

Hopefully it doesn't follow the swap. If it does you have a wiring issue on the harness itself.

 

The wiring has been checked several times in the areas we will be using. The EGR and BARO are not going to be used.