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Discussion Starter · #1 ·
After 4 months down time swapping out the rear suspension, I finally got a chance to test the car last night. The primary focus of the testing was on the suspension and that was very successful. For folks who are unaware, I swapped out the Nissan IRS for a Corvette C4 IRS with a 3.07 LSD. Any concerns about losing a little off the line with the tall gearing was put to rest with a 1.60 60' on an easy 4# launch with BFG DRs. I can definitely see 6-7# launches putting the 60' solidly in the mid-1.50s. However, I am getting a mysterious code 55 which indicates I have a malfunctioning ECM. Not sure if it is related, but on the 1-2 shift, I got the code as the RPMs dropped to about 4,500 from a 5,375 shift, then the car stumbled badly as the RPMs plummetted to 3,100, not good with a Max Effort. In addition, the car was running pig rich and we had no time to tune.

I listed the details on the code below. What I find interesting is that the A/D converter reads sensors, like the TPS, and sets the code if it cannot properly read the sensor 24 times. On DirectScan, the TPS wass solid but I do have a Volt-Booster connected to it. On a previous run, the V-B increased the voltage to 15.1V, then about 1/3 way down, it dropped to 11V. On the next run, the car completely lost power a couple of times before I shut it down. On the last run the V-B appeared to work normal. Before I draw any conclusions, I wanted to see if anyone has experienced this and get some input from the forum. I do not want to rush out and swap in an ECM if that is not really the problem.


Trouble Code 55 indicates that the Analog-to-Digital (A/D) converter in the ECM is faulty. This converter reads sensors (e.g., TPS, Oxygen) and coverts their analog voltage output to a digital number for use by the ECM. If the converter fails, the ECM sets this code.

The conditions for setting this code are:

the A/D Converter has failed to properly read a sensor after 24 attempts.

Typical causes for this code include:

1) Defective or incorrectly inserted PROM
2) Defective ECM

If replacing the ECM, be sure to transfer both the PROM and the CALPACK from the old unit. If the old ECM also indicated PROM failure (Code 51) or a bad CALPACK (Code 52), be sure to verify these components are fully operational in the new unit. If they are not, they too will have to be replaced.


Scottie's GNZ

71 240Z/GN Power/Corvette IRS

1,797 Posts
Sorry to hear that, especially after all the hard work of the rear diff swap.
Well, I'll just throw some stuff at you... Faulty volt booster or faulty grounds causing a spike, voltage regulator in the alternator going south, bad DirectScan connection.

Hope you find a quick and easy fix to this this gremlin.


1972 Toyota Celica with a 87 TR drive train.

PTE 44 turbo @ 20psi on pump gas. Jay Jackson’s 62 mm throttle body, ported and polished plenum and intercooler. Solid MAF pipe, K&N Filter. Blue tops. Hot wired 255 L/hr Holley inline FP., AFR. AC CR43’s. Type II coil pack and module. 8.5 Magnecor’s. Hand made TH style DP, 3” exhaust split to two 2 ½ inch Magnaflows.

Built 200 4R tranny, B&M cooler, stock D5 converter, B&M Megashifter.
Chopped Ford 9” four link setup @3:25 posi rear with a 300 ZX disk brake setup. Air bags, Bilstein Rally shocks.
85 Supra 57 mm piston 10” vented rotor front brake setup. Hurst Roll control. Tokico race struts, heavy duty coils. Nissan 300 ZX 15/16 master cylinder.
Dunlop SP 5000 205/50ZR 15’s, Ford power steering rack.

DirectScan, Caspers Knock gauge, Autometer 30/30 boost/vacuum gauge, Autometer tranny temp gauge. Jay C’s 94, Red’s 100, Thrasher 92, and my own chips
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