Lotus Esprit GM EFI conversion project...

[JeffS]

Hi Everyone: I have a 1986 Lotus Esprit equipped with Bosch K-Jetronic fuel injection and standard distributor setup. We Lotus owners have a saying about the K-Jetronic.... It doesn't throw codes, it throws fits. And the distributor sitting under the throttle bodies has been the source of many an Esprit engine fire. So the goal is to convert this engine to electronic fuel injection, which Lotus actually did in 1989, using the GM 1228708 ECU with the D1927 ignition module running in wasted spark mode. They notched the outside edge of the flywheel and added the crank position sensor there at the back of the engine, I think because the crank pulley at the front of the engine is in a very crowded spot. I have managed over the years to acquire all of the original 1989 OEM intake hardware... intake manifold, throttle bodies, fuel rails, injectors, etc. But I do not have any of the electrical parts... primarily the ECU and wiring harness. The 1228708 ECU looks to be available without much difficulty. If my info is correct it was used on 1990-1991 Oldsmobile Cutlass Supreme, Calais, Buick Skylark, Pontiac Grand Am, and Chevy Beretta.... basically anything GM made with the Quad-4 engine option. The Lotus specific MEMCAL however, looks to be super rare. John Welch at W C Engineering has the last and best BIN files for my Lotus 910 engine, but that still leaves the Lotus specific ESC (knock sensor board) and resistor networks to complete the MEMCAL. So right now I'm looking for information.... a schematic for the ECU 1228708, sources for donor wiring harness and connectors, any information or schematics of the ESC (knock) circuit... not necessarily Lotus specific but great if it is Lotus specific, and any information on the resistor networks and what they do . I look forward to hearing from everyone.... Jeff

[ATSAaron]

Hello fellow Esprit owner. I currently have a 77, 88, and 91. I've previously owned an 89 and two 1990's. I make (and sell) the absolute best chips for these cars. I've seen the code for all the Puk and other chips. They do not match what they claim at all. Ironicly I'm going to tell you to get a full stand alone instead of the GM efi setup. There are lots of little issues with the original ecu, like they are only happy with a very specific and rare injectors. Plus the MEMCal alone is $$$$ (if you have one, I need one). It's funny that half an hour ago the same idea hit me about my 1988 car, that I should put a stand alone ECU on it instead of the CIS. My shop (ATS Exotics) previously converted a 1984 to EFI and my 1977 has EFI. It's pretty easy use the distributor as your engine position sensor and run a batch fire injection setup. You can buy an ECUMaster EMU Classic and flying lead harness for about the same cost as just the MEMCAL, or if you wanted help we can sell you the ecu and a completed harness along with support getting it started and tuned. Sorry, I didn't mean for this to be a sales pitch. Either way you decide to proceed, good luck with your project. BTW I rarely visit this forum and was only here looking for information on a knock sensor board that might work on the Lotus [email protected]

[JeffS]

BTW I rarely visit this forum and was only here looking for information on a knock sensor board that might work on the Lotus [email protected]

Hi Aaron: I've gotten the same warning from John at W C Engineering about all the "Improved" Esprit BIN files out there... that nearly all have virtually no fuel or timing table improvements, just modified safety limits... Yikes! Actually, I've got a source for the latest S4s code, but as you say, the ESC (Knock Sensor Board) and resistor nets looks to be super rare. Being an electrical engineer specializing in high accuracy analog circuit design for the last 40 years, I'm sure I could duplicate the ESC circuit in modern surface mount components. But alas I have not been able to find any internet info on the knock sensor circuit, nor a real Lotus ESC board to back engineer and measure. I did recently purchase a 1228708 ECU for $12 from Ebay and it should be delivered today. Despite having the wrong ESC and resistors (it was pulled from a 1990 Quad-4 engine) I'm sure I will get $12 worth of entertainment from pulling it apart and seeing one of these ESC boards in real life, even if it is not the one I need. This is a deep rabbit hole I'm diving into. Even if I managed to duplicate the Esprit ESC, I'm not really sure if there are any others out there who would want it at this point.

[sailorbob]

The D1927 ignition module will not work with the stock Esprit code if you want to keep the semi-sequential injection. The netres can be duplicated easily enough (I know of someone who designed a replacement board that uses through-hole resistors) but the ESC filter is unique and there are two versions, one for the 2.0L engine and another for the 2.2L engine (that said, I've seen Lotus use an ESC filter with the 2.0L 1.0k ID resistor in a S4s Memcal). There are some ECU schematics floating around on the 'net although I cannot recall if the '708 is one of them. Search for 'ludis p4 schematics'. Running different injectors is not an issue if you are willing to run a modern high impedance injector like the Siemens Deka IV and alter the code to avoid error 65.

[JeffS]

SailorBob:I've spent about two weeks of evenings trying to scare up any info on the ESC board and resistors. The 1228708 ECU is available (less the memcal) so my plan was to create a new memcal board with electrically erasable PROM instead of UVPROM, and duplicate the resistor nets and knock circuit in surface mount components. Pretty straight forward I thought. But not if I can't find any information on those circuits. Of course the other question is if anyone else would benefit (want a copy of) the reimagined memcal? I'm not sure there is much of a need. I'd keep digging if there was a clear need. The straighter faster path for me looks like going with an aftermarket ECU / harness kit, map the tables over from the S4s code, and start from there. But thanks for the leads.... I'll do some googling tonight. Jeff

[ATSAaron]

SailerBob is like Lotus ECU royalty. He helped me in the past with the error code 65 on an 89 I had. Pontiac GrandPrix injectors are 36lb, high impedance and work perfectly once that code 65 is gone. Aaron

[sailorbob]

I do not think I have ever seen a schematic for a P4 ESC filter so I suspect you will have to reverse engineer the one from the Quad-4 ECU. There are probably all very similar with only the capacitors and resistors changing to alter the frequency and gain characteristics. A replacement ESC filter would be good thing as it means there would be a way of keeping the OE ECU if the ESC filter failed.

[JeffS]

Does anyone know exactly what the columns mean in this chart: https://i.postimg.cc/vH0WjsGV/Memcal-ESC-info.jpg

[JeffS]

Looking at this patent: 4,111,035 ENGINE KNOCK SIGNAL GENERATING APPARATUS WITH NOISE CHANNEL INHIBITING FEEDBACK, they describe a knock sensor circuit with a front end amplifier combined with a bandpass filter. That explains... FIRST STAGE FREQ, GAIN, and Q. Then there is a lowpass filter into one side of a comparator... COMP GAIN, OFFSET, and LPCF (perhaps Low Pass Cutoff Frequency?). I have no idea what NOISE CHANNEL ITC/DTC is? And any guesses about what IGN, or AOT means? ID RES (in Kohms) is obviously the identification resistor. I'm entertaining all guesses at this point.

[JeffS]

A completely different approach would be to build a better than original knock sensor using modern digital signal processing techniques. For example sampling the knock signal and running a real-time correlation with a known stored knock signal in a small DSP chip. As I'm saying this, the aftermarket ECU approach keeps looking better and better...LOL

[1project2many]

Hello and welcome to the forum!

In the US the 1228708 ecm was used in GM vehicles equipped with a Lotus designed 2.3L engine in 1990 and 1991. The 1228707 is a functionally equivalent version but in a water resistant case to be mounted in the engine compartment. I have not yet found these ECMs in Australian applications, although a very similar part number 1227808 ecm is very common.

There's some very interesting information about GM knock sensors in this thread. There's also a link to a chart which shows important details about specific GM knock filter / amplifier circuitry including filters for the Lotus 2.0 and 2.2.

I've spent some time reviewing GM patents. I believe US4384473A covers some or all of the knock sensor circuitry. The "Noise Channel" concept from the patent appears to be reflected in one group of specifications from the chart. It may be possible to use the patent and the chart to understand how the knock filter is designed and potentially to find an alternative knock filter/amplifier (GM termed it a Signal Noise Enhancement Filter) that is acceptable.

[sailorbob]

See post #'315 in this thread for info on the column labelling in the P4 ESC filter spreadsheet picture. https://www.gearhead-efi.com/Fuel-In...997-F-Body-ECM

[JeffS]

Holy Cow SailorBob.... You really pulled a rabbit out of your hat with that reference. I'm afraid I've got a hobby for tonight reading through that thread to entry #315. It certainly is great to find members with deep gearhead-efi memory.

[JeffS]

So I've made some progress on the ESC chart along with SailorBob's above reference to post #315. Patents 4,276,861 and 4,384,473 describe nearly identical circuits that align well with the ESC circuit from this time period. Together with the above reference we have: MASK = mask set used for manufacturing. SBST = substrate type. FREQ, GAIN, Q describe the first stage bandpass filter center frequency, gain, and Q. COMP GAIN = compressor gain. LPCF = Lowpass filter cutoff frequency. GAIN, OFFSET ITC/DTC are the gain, DC offset, increment time constant, and decrement time constant. IGN is the ignore-time = the amount of time (in milliseconds) that is ignored before a knock pulse is declared. This removes narrow noise pulses that are not caused by true knock. AOT = add-on-time (in ms). When a pulse is big enough to exceed the ignore-time, the add-on-time is added back to the pulse length to restore (or enhance) its original width before it is sent to the ECU.

[JeffS]

Having dealt with patents in the past, I can tell you that authors will sometimes intentionally obfuscate what they are doing in the explanatory text and examples. Only the claims really matter. So despite there being a pretty detailed schematic of the knock sensor circuit included in these patents, only tracing out a real ESC board will convince me that I have the schematic correctly drawn. But you never know... maybe the preferred embodiment described in these patents is exactly the circuit that's in there. One thing the P4 chart does show however is that a large majority of these different ESC boards all start out on substrate #2, using mask set 7KR. That means that the resistors are all printed with the same starting pattern. Laser trimming the resistors, and populating with different tuning capacitors give each board its unique characteristics. So that means that any of these MEMCALs could be used to trace out and verify the circuit topology.