355 2.7 MAF SENSORS

I want to reach out to the 355 community to ask for some help.
To start, my car is a 1995 2.7 and I have owned it since 2016. The issue is every once in a while it will just lose power but not stall. Like I'm losing half of the engine. At first, I would get a 1-4 cel, read codes and get lambda along with loss of crank signal. (which I understand is normal while reading codes with the engine off)
I want to stress that this issue is extremely intermittent. Parts replaced to date include both crank sensors done while engine out, (cracked connectors) 1-4 ignition coil and module, new plugs and wires during major and both SDECU's as they were original.
I know most parts are 30 yrs old and I have no issue with replacing with new.
I would also like to add that in most cases the issue goes away before I can even pull over, and now I haven't got a CEL in quite a while. What have folks here experienced when their MAF sensors go bonkers? I know with GM vehicles of like vintage, you would get a stall or very rough running. But thats with one per engine, the 355 has two. Any ideas? Thanks.

 

I had this issue on mine (extremely intermittent and often just restarting the car would fix it) and I think it was related to the cat temp sensors as it would throw a light every so often despite, at the time, not having cats. At the last major I found a badly cracked cam sensor connector so replaced that and cleaned all contacts when I had it apart, and have not had a single issue in the year since. My diagnosis is an extremely intermittent poor contact somewhere. I used non residue spray contact cleaner along with some dielectric grease on each connector when I re-assembled.

 

Thanks for the reply. I thought the cam sensor was just for startup to align the crank sensor to cam, then after startup the ecu just uses the crank sensor. Also you stated that your car was stalling?

 

No, I'd lose a bank every so often. It never stalled out. '95 2.7 with twin fuel pumps.

 

Does anyone have a resistance measurement spec for the cam phase sensor?

 

Had similar symptoms losing banks 1-4. Early F355 model.
The power line crimp in the wire harness was making intermittent connection causing one of the ECU's not to be on. Cleaned, reconnected the wires, now all good.

Good luck, these issues aren't fun.

 

Do you remember where in the harness the splice was? I have tried wiggling the wiring connectors and harnesses with no luck but if I knew where this splice was I could check it out. Thanks.

 

Yellow power wire

1st image is where to check
2nd image is of rolled back wiring sheathing from the bundle going to the left ECU back to where the line splices, and the wire was loose
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Can you recall the codes? The crank sensor wiring is known to fail (on the ECU side, not the sensor side), close to the sensor connector.

I couldn't find any resistance values. Are you getting a voltage at the sensor? It's a Hall Type sensor, so needs 12 volts on pin 1 on the 2.7. Pin 3 is an earth.

 

Thermocouples.

Replace or splice them together.

 

https://www.ferrarichat.com/forum/threads/2-7-thermocouple-question.391935/#post-142254856

Thank me later

 

Thanks for the info! This makes sense, as this yellow wire (splice) feeds the injectors. There is another splice that serves the ignition coil that I will check too. Thanks again

 

If the thermocouples were suspect wouldn't I get a SDL along with the dropout?

 

I checked the crank sensor wiring while replacing the sensors, and couldn't find any issues.
I will check the voltage and ground on the cam sensor, but if I were to lose this signal would I get a loss of cylinder(s)? I am under the impression that once the engine starts the cam signal is no longer used for injector/ignition timing? Thanks.

 

I seem to remember someone having an issue with wiring here:

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Externally, the damage was not visible. You had to flex the harness with the engine running to reproduce it.

You may be right. The WSM is rather ambiguous when it comes to "timing sensors"

 

I know John K had an issue with the wiring pulling out of the connector pin. I ran the car on the lift and pulled and wiggled the harness to try to get a response. No luck

 

Actually, it didn't pull out. The wire broke just behind the crimp to the connector pin. Since part of the crimp is over the insulation it held the wire in place but at times vibration would make it loose contact and one bank would go out at a certain RPM. I found it by pulling on each individual wire and on on the insulation stretched like a piece of rubber on the broken one.

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I wasn't able to find any issues with the two splices, but I am still on the hunt... Thanks for the tip

 

I am still trying to get this sorted, but the issue is so intermittent that it's like chasing ghosts. Back in the old days (OBD 1) we had a GM data recorder that we would plug into the DLC and it had a pushbutton for the customer to push when the problem arose and then we could read the snapshot later. Unfortunately I will have to rely on my DVOM and some luck.

 

John, I had an MAF failure on my car a couple of years ago while out driving. Also a 2.7. The symptoms were that I had to play with the throttle to keep it running at idle (stop signs and such) and throttle response was poor. But once I got moving at more or less constant speed it drove pretty normally. CEL would flash on and then off. When I got home and check the codes it had the 1111 code for the MAF. Your problem doesn't sound like an MAF problem to me.

I've also had a coil fail intermittently. When that happen I lost power and if it stayed out long enough I got an SDL. The SLD would go out when the ignition came back. I replaced the coil and power module (just to be sure) and the problem was solved. I know you said you have replaced those parts, but....

One thing you could do is get one of those hand held scopes and connect to the power module to see it it is grounding the coil. But you have to do one side of the coil at a time and drive a round until the problem pops up. And if it's connected tot e wrong side you miss it. But be careful because when I did something like this on my 308 I kept looking down at the scope instead of the road.

https://www.walmart.com/ip/Daakro-FNIRSI-DSO152-Handheld-Small-Oscilloscope-Portable-Digital-Oscilloscope-200KHz/3859348032?wmlspartner=wlpa&selectedSellerId=101185227&adid=222222222273859348032_101185227_14069003552_202077872&wl0=&wl1=g&wl2=c&wl3=42423897272&wl4=pla-295289030566&wl5=9003183&wl6=&wl7=&wl8=&wl9=pla&wl10=586014927&wl11=online&wl12=3859348032_101185227&veh=sem&gad_source=1

 

I do not know for sure whether the cam sensor is used all the time or only at the engine start-up but, if the 2.7 355 (like the 2.7 348) has only one cam sensor shared by both ECUs, any failure/malfunction of it would affect both banks, not just one. I think that in your case (and if the 355 has only one cam sensor) the cam sensor malfunction can be ruled out. Otherwise, the cam sensor (Hall Effect type) cannot really be tested by reading resistances between any of its 3 wires. You can test a Hall Effect sensor as shown on this diagram:
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The LED will light-up and go off as you pass a screwdriver in front of the sensor.

 

Thanks for this tip. I think this will be my next course of action, as I have a gut feeling that I'm losing park and not fuel. The only other culprit that I have my eye on is the ECM. I plan to swap them, but as of recently I'm not even getting a CEL so I dont expect this to bear fruit.

 

I actually found 2 new thermocouples in my cabinet last night that I meant to install during my major but overlooked. I plan to install them. However--just to be clear I am under the belief that if I am losing one bank and the thermocouple or the SDECU was the culprit that I would get a SD light. Also, there was a time when I was able to pull over while it was skipping and I unplugged both t-couples and the ecu's and it didn't change anything except getting the SD lights on the dash while they were unplugged

 

Yes, that's the problem. If you don't get a cel or sdl you don't know which bank is the problem.

I got that little scope because I was having a similar problem with my 308. I would lose a bank for a second and then it would come back. I hooked up my regular scope in the garage to the coil triggers on each bank to see if they was firing. Sure enough I found one side was not firing (coil not grounded) intermittently. But I could tell which Digiplex was the problem. I had to trace the wires back to the Digiplex units (308 ECUs). Then I drove around with the little scope connected figuring if it does the drop I would know which unit was the problem. Anyway, long story short, after screwing around with the wire it never did it again. So I figure it was a loose connection. This stuff will drive you nuts if you let it.

 

Tell me about it. During my major I removed every connector and checked for proper pin retention and cleaned them with contact cleaner. Sooner or later it will reveal itself