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My 87 has been my daily driver for over 3 years. I was at a stop light this past weekend and the tach started jumping around, no engine rev change, just the tach jumping and voltmeter jittering. She then died, she didn't immediately restart so I pushed her into a strip mall parking lot and tried again, no joy. I checked fuses, none blown, relays weren't hot, unplugged and reseated LH connector and she started and I was able to drive home.
I was finally able to check a bit deeper tonight and when I started her the tach did same thing, voltmeter also reacts and car dies. It did start right back up but with same issues. there has been no recent work on the car, I did replace front engine harness with one from Sean last summer. I put a meter on jump post and it reads 13.96-13.98 volts while car is running. I put fuel pressure gauge on rail and it's a solid 58 psi.
Where does Tach get it's signal and is that a logical place to start? Below is a link to a short 30 second video that shows the tach bouncing around.
I have been working with Kevin to solve this issue and it seems to only to be getting weirder.
The current CPS connector has what appears to be a break in a wire at the sensor end. It also the only CPS that the car will start with.
Kevin has bought 002 and 003 CPS versions and either the car does not start or it starts and dies.
He has swapped relays and computers and nothing helps. He jumpered the FP relay no change.
Fuel pressure is 58.
My recollection from when this first started was that the injectors start clicking and then stopped when the engine quit. I also seem to remember that the spark was never lost. I'll ask Kevin to confirm the latter.
I like an automotive mystery as much as the next guy, but this is getting to me.
Did you disconnect the battery after swapping in a new cps
this will reset the computer
have you replaced the MAF and done a battery reset do one thing at a time to isolate the problem
also check battery connections and ground strap for corrosion
I have disconnected battery as well as the LH, EZK, CPS and MAF. battery ground is clean and ground strap is less than 6 months old, the grounds on either side of throttle wheel bracket are clean. The MAF was rebuilt by Injection Labs 3 years ago. I do have a couple others so can try another one to rule it out.
The original CPS has had a new male connector added at one time. Here are a couple pictures of both ends.
My personal opinion is there is an issue between the sensor and the computer. Old CPS is allowing a louder signal to get back to the computer. I'd Ohm the three wires to their destinations. Additionally, I'd like to send off the CPS sensors to be verified using a oscilloscope. Finally, if money were no object I'd fork over the $$$ for a Porsche unit. I really believe given that everything that can be swapped has been swapped the only piece of the puzzle not verified is the harness.
Had some time this evening to dig a little deeper. Per the WSM the wiring at the harness plug should be #1 white stripe, #2 brown nd #3 ground. As you can see below someone wired it #1 brown, #2 white stripe and #3 ground. Both harness and CPS have same wiring so everything fine with the specific CPS and car. Try to install a new CPS and no joy. will get the harness plug fixed and things should be good!
When I have replaced harness and sensor side connectors I take multiple pictures to get this right the first time. This is the first time I've encountered this kind of shoddy work.
To follow up and put a bow on this. As I said in an earlier post, the connectors on both the harness and CPS sensor had been replaced. The wiring was not per WSM but matched to each plug so car ran. Had a professional automotive electrician come and install a new harness connector with correction wire orientation.
As an FYI, make sure that the harness wiring is oriented with the notch in the harness plug up otherwise your wiring will be exactly backwards...ask me how I know. Quickly popped out the terminal connectors, reinserted and car fired right up and after about 10 minutes running very smoothly.
04-19-2018, 08:08 PM
87 Auto dies - erratic tach
