The car is a 1989 Marelli that was purchased with damaged ignition wiring in the valley, and the car didn't run. Most of the damage was confined to the coil and amplifier wiring. I removed all of the repairs and rewired it since there were still a lot of bare wires and plenty of wires with brittle insulation.
Both sensors were replaced and gaped
The amplifiers were replaced (one was damaged electrically)
New rotor, cap and plugs
The fuel rail and injectors were removed and cleaned
The signals to the injectors were checked good when cranking
The fuel rail pressure is about 35 psi
It doesn't run with start fluid sprayed into the intakes
It did start on three occasions after the repairs. Twice about 5 seconds and once for 45 seconds
Hasn't started since
The distributor/rotor was aligned with the TDC mark
The coils spark regularly and each cylinder appear to as well (using an inductive timing light)
The engine backfires out of the exhaust and intake manifolds
It appears the timing is off from the ignition signals out of the computer see the scope picture.
Any help or insight is appreciated. I'm pretty close to having this running but there seems to be an intermittent problem or something I don't understand. Thanks Mark

 

timing at startup is determined by the front crank sensor for the marelli system , once started this sensor is redundant, it determines TDC for the ecu

the other sensor is on the flywheel opposite side to the starter motor, this is constantly checked by the ecu for engine speed , and needs to be within 2thou of the teeth , as does the front sensor
other systems that prevent Marelli cars from starting is the front left water temp sensor, and the air temp sensors , these will allow the car to crank , but not fire



just a tip on the injectors, these are always live from the relay in the boot ( trunk ) and switch down through the power resistor behind the right front headlight, and then this travels to the ECU in the boot by the battery which switches the voltage to ground in the ECU ,

injectors are switched in four banks of three A1,3,5 A2,4,6 B1,3,5 B2,4,6 , not in that order though

BB

 

The coolant sensor reads about 3k ohms as read from the ECU connector. The air temp sensor is was replaced with a new one. It reads about 2.4k ohms from the EFI ECU connector. Are these about right?

Looking at the traces on the scope (first post), the top trace is the TDC sensor. It is at 8 degrees ATDC of the A Bank. I think the B Bank should be firing about 48 degrees after that. But the third trace is the B Bank and it is firing right at the TDC mark. This doesn't look correct. The A Bank looks like it is firing at about 60 degrees after the TDC mark when it should be firing just before the TDC mark. Am I confused about this or are the ECU output signals wrong?

 

A few things to check. The coil that is fed with the white brown(lower coil), its coil wire should go to the center post of the distributor cap.

Make sure your crank trigger and your speed sensor are not reverse polarized (wired backwards).

Did you splice new wiring onto the harness? If so, what did you use for the coax?

Worth mentioning - Since the crank rotates twice to the cams one revolution, putting the rotor on at TDC means you are either spot on, or 180 degrees off.

 

I bought my 89 Marelli car not running as well. I rebuilt the ignition harness, tried starting fluid, checked fuel pressure, compression, timing, literally everything I knew to check. Even sent my ECU to Mike in Ohio. He plugged it into his 1990 Marelli car, and it fired right up.
I don't know if you ran new coax for the front sensor, or if the coax on your rear sensor was damaged, but take my word for it....twisted pair WON'T work!! Not shielded as the schematic shows either. It HAS to be coax!!! On top of that, they HAVE to be wired correctly according to polarity. My rear "sensor" was wired backward.
Those "sensors" aren't sensors. They are small electromagnetic generators. The rear sensor will give the ECU about .6 volts AC at starter speed (300 rpm?). It will go uo to as much as 80 volts at full throttle.
I'm not a electrical engineer, and really don't understand Hertz, as well as all of the other things associated with this system, but believe me, when right, it will fire right up. Thanks again to all those on here, as well as another Jaguar forum for helping me sort it out.

 

Cat, thanks for the reply. As for the polarity on the sensors I made cables to reverse the polarity of both sensors and tried all of the combinations reversing each by itself and both at once but no difference. The timing and outputs to the amps didn't change (looking on the scope).

The lower coil wire does go to the center of the dist cap.

As for the coax the flywheel sensor coax wasn't damaged. I did change the connector on the TDC sensor. It has a couple of inches of straight wire, but the signal at the computer is still good. It looks like the signal in the manual. The coax running through the valley wasn't damaged. Looking at your before picture, I had much more wiring remaining than yours.

I did rotate the rotor 180 degrees and cranked it. It was obvious that wasn't correct given all of the backfiring.

Sending the computer off for a sanity check would be good and I'd like to have Mike's contact info.

 

I wish you lived down the road so I could come over and see it with my own eyeballs.

 

Looking at the trace it seems that the B amp is being told to fire at TDC 1A, Have you tried swapping the coil inputs to the dissy?

The 3 tooth wheel as you know indexes 1A TDC, firing of the B amp is calculated by the Marelli ECU

 

Warren, yes I have switched the coil inputs to the distributor. It still wouldn't start. I also thought for sure I would find a wiring error (my own error) switching the A and B bank signals out of the computer. Checked last night and it appears correct. Am I using the correct wiring diagram? I attached what I am using.

Speaking of the 3 spoke wheel on the front damper, I haven't made certain that 1A is at TDC (or 8 deg ATDC) when the mark is aligned. (also on the compression stroke) I recently bought a USB borescope to look inside the cylinder with the marks aligned. There are a couple of paragraphs in Kirby's book describing sheared keys on the crankshaft allowing the damper and in turn the sensor tabs to rotate on the shaft and get of time. Hard to believe it rotated 40-some degrees though.

I've attached a timing diagram that was found on the web. Not sure how accurate it is but looks correct.

 

The timing seems to be 60° out. So if it is the 3 tooth reluctor then this is 60° out. you will need to line up the tooth to the VR sensor and check 1A is TDC.

The wiring diagram you have is correct for the Marelli. If this does not work you will need to re-check all of your wiring again.

 

The 1A cylinder is at TDC when the TDC mark is aligned on the front pulley. I checked this by looking in the cylinder with a endoscope camera. The cylinder was also on the compression stroke, so I checked the position of the rotor. The 'A' side of the rotor was right on the slot of the distributor body.

I've checked the wiring enough times now that I'll probably get someone else to verify it to catch any stupid mistake or bad assumptions I may be making.

Does anyone have a Marelli computer that they would be willing to sell? The computer could be in known good or even unknown condition. My part number is 122 JADAC 7485 0530.

Would anyone be willing to plug my computer into there car?

Thanks Mark

 

I don't have a spare, but I can plug yours into my car. I'm crazy like that.

 

.

 

The Cat, thanks. I do want to try one more thing before sending the computer off. I'll let you know when I send it. Should be this week.

Does someone know how many teeth are on the flywheel of an 89 Marelli car? I counted 160 by looking at the inputs to the computer with the scope. That gives 2.25 degrees per tooth. Is this correct?

 

Repair operation manual states 160 teeth per revolution

 

Paul_59, Thanks for the tooth count on the flywheel. That's helpful.

I'd like to dig a little deeper into the computer. I'm fairly certain that's where the problem resides. Does anyone have a schematic for the ignition ECU circuit board?