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760 SW 1990 Turbo No Spark, no pulse

dialex

New member
Joined
May 22, 2009
Location
Tampa, FL
I have been troubleshooting my daily driver for 4 weeks now and cannot get it to start. Car has 242k miles (still new) and symptoms started one morning in October when Car started stalling and shut down on me. Was able to restart and drove home in limp home mode- if I gave it more gas it will stall, so kept my foot off the pedal and got home.
My immediate though was AMM and I cleaned it, put it back on, car run perfect, but when I was about to leave the house- no start, so I started troubleshooting - changed RPM sensor as wires were showing from insulation, put new distributor and rotor, plugs, swapped the powerstage and the coil, still nothing, then all of a sudden spark showed up but still no start, checked the fuel pump and FPR, unplugged return line of FPR gas flows strong, swapped FPR with a spare, nothing... hooked up Noid lamp to injectors and pulse was there too, along with the spark, but still no start, drained a plastic bottle from gas tank and compared the gas with another plastic bottle - checked for water, seemed normal, was about to drain the tank anyway and fill with new gas, but then I lost spark and pulse...Oh took the ECU out and plugged it into my 780 230FT and car ran fine, also swapped ignition computers ??? still nothing
Right now I have +12V at coil even when the key is out of the ignition, ( and wire is pulled from the coil) swapped few radio sup. relays, swapped AMM with the 780 and still nothing, took apart the connectors at the strut tower F and C LH and also the other two on the RH side- silicone was bad and will need new ones, but for the time being, cleaned the wires and plugged them back in. As of right now I am suspecting a short somewhere, any thoughts?
 
Seems like you may have a couple of issues. You should not have 12v at the coil when the key is off. That is supplied by the key but on your car it may go through the suppression relay. The electrical part of the ignition key can get carbon tracks and become intermittent. So that may be one suspect.

I also don't trust the amm. When they fail completely they can let the engine run at idle but you can't rev the engine at all. I've also had them fail where you car starts but won't stay running. Just misses and pops until it stalls. I would definitely either disconnect it and see what happens or try another one.
 
Thank you for the responses, Last I checked there were no codes, but that was in the very beginning, I am going to check the codes again, and yes I don't trust the AMM- has failed me once before and threw in a used replacement from one of my other cars. Fuel pressure is good - nice and steady flow from the return line- I have own the car since 2002 and know every noise in it, also I did swap FPR just in case in the beginning, also sprayed starting fluid in cylinders- still nothing. Will pull codes again and will post the results,
 
Finally got some time and did a lot of tests this afternoon:
There were no fault codes and I guess the +12V present at the blu wire at the coil was due to me not connecting the "D" 8 wire connector at RH tower properly, which I took apart for cleaning and all the wires got mixed up, but today I used the schematics to reconnect them the right way as some of the colors faded over the years and was not easy, specially for the wht/blu and wht/sb wires, then I went to System Sensor Signal Test and I tried the TPS test first- it gave me 3-3-4, then disconnected coil wire and attempted to test RPM sensor, which was purchased back in 2003 and kept as a spare until all this happened and the light continued blinking, indicating faulty TPS. So I am ordering a Bougicord (Volvo P/N 271949) sensor from FCP and hopefully will be able to start it up ( I like the XC90 2.5T but I am getting tired of it)- I miss my 760 every day. Also will get some water tight connectors:

https://www.amazon.com/Summer-Home-Motorcycle-Waterproof-Electrical-Assortment/dp/B074FYXGZJ

and get rid of the big rectangular ones, will solder and shrink fit every wire individually, the new connectors provide a lot better protection,
Will update as soon as I receive the new sensor,
 
Finally got some time and did a lot of tests this afternoon:
There were no fault codes and I guess the +12V present at the blu wire at the coil was due to me not connecting the "D" 8 wire connector at RH tower properly, which I took apart for cleaning and all the wires got mixed up, but today I used the schematics to reconnect them the right way as some of the colors faded over the years and was not easy, specially for the wht/blu and wht/sb wires, then I went to System Sensor Signal Test and I tried the TPS test first- it gave me 3-3-4, then disconnected coil wire and attempted to test RPM sensor, which was purchased back in 2003 and kept as a spare until all this happened and the light continued blinking, indicating faulty TPS. So I am ordering a Bougicord (Volvo P/N 271949) sensor from FCP and hopefully will be able to start it up ( I like the XC90 2.5T but I am getting tired of it)- I miss my 760 every day. Also will get some water tight connectors:

https://www.amazon.com/Summer-Home-Motorcycle-Waterproof-Electrical-Assortment/dp/B074FYXGZJ

and get rid of the big rectangular ones, will solder and shrink fit every wire individually, the new connectors provide a lot better protection,
Will update as soon as I receive the new sensor,

Crank sensor was my first thought.
 
I've got a 700-series ignition greenbook that I'll email you if you PM me with your email address.
 
Sounds earily like my problem that was quickly turned to my wasted spark install......spark and injector pulse but no start. Post a result if found please.
 
Well none of the above makes any sense, especially the incorrect wiring on the strut post. If the ignition switch is "on", there will be 12v on both terminals of a coil in the average vehicle. The amplifier will periodically ground one end of the coil. Volvo modules don't give you access to both ends, but the standard spark test can still be done. Place plug on grounded metal, crank, and observe spark. Simple. Radio suppression relay (fuel injector relay) is the next typical place to go. My 940 does not have sequential injection, so the relay is on all the time. Quick test there is fuel on the plugs.
-Lazarus
 
Finally got little time today, was doing few things to my new XC70 2007 2.5T 62k miles, (just got it yesterday), but did receive the sensor and stopped working on the XC as soon as the mail lady came, and ran to my old wagon, took out the sensor, put the new one in and ...nothing, no spark no pulse, basically no change, then temperature dropped quite a bit and decided to go inside.
I have a green manual for wiring diagrams from October 1989 TP 31565/1 for 760, (if anyone needs it, I have it in pdf format, will be glad to share it) and all the wire colors are matching my car, I have checked the radio suppression relay multiple times, even have jumped it few times, so I am ruling this out, next time will start digging more into the wiring and look for a short somewhere, I've checked all the grounds on the intake, marked "H" and they were fine, noticed a wire from the alternator going back to the starter which looks oil damaged and it is stiff to the touch- will replace it and maybe will try disconnecting individual components/sensors one by one and attempt to start, there has to be a short.
Thank you all for your support and I will keep posting updates on this 8 week long problem( longest in the 18 years I've owned the car)
 
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A buddy had a '90 model that took us a couple of Sundays to get sorted out. The book I offered has a step-by-step diagnostic procedure that finally got us back on the road.
 
Well after few busy weeks, finally got to it last weekend and gave it a wash, moved it to the garage and unpacked my new Oscilloscope, after everything was hooked up, cranked the engine with a little breakout adapter at the firewall so I connected the Oscilloscope to #1 and #2 of the sensor and when cranking, signal was there( will upload a Video shortly) so then I traced it to the connector of the ICU #10 and #23 but noticed it was not there and when moved the connector at the firewall- it came on. I guess when I was trouble shooting the sensor connector with my Multi meter I accidentally have bent the inside of the female connector and therefore was not making contact with the sensor. Used another plug and made an adapter just for testing and realized I might have done the same to the 23 pin connector at the ICU, this time just used a sharp object and straighten the pins, and I was actually hoping that the car will start, but...no still no start, but when I looked at the mirror in the engine bay there was a beautiful spark coming up at cranking and also there was the injector pulse on the Noid light, so I guess I was back to where I begun after the car quit on me.
And at one point I was suspecting bad gas or water in the tank, did drain a little in a plastic bottle and compared to good fresh gas. but then lost the spark ...Next steps are pull injectors to clean or replace them drain the 12 gal of gas, possibly use aux gas pump from a can
Anyway will post video ASAP, can't wait to get back into my Wagon.
 
Nice use of a scope!

Never front probe terminals without the proper tool. Stuffing multimeter leads into terminals can damage the terminal and cause a loss of terminal tension.

Does it run on brake cleaner? Click my sig.
 
Lesson learned, first part of the video I am testing the sensor, and second part is all hooked up after repairing terminal connectors at ICU and power stage. to the left is the Noid Light and to the right is a mirror in the engine compartment on which you can see the spark:

https://youtu.be/YZ52CHww2T4
https://youtu.be/YZ52CHww2T4
 
There should be a +5 volt square wave at the input to the ignition amplifier. It comes from the ECU, and is easy to track down. Place one plug on metal and crank, observe spark. If it looks like a healthy spark, you are out of time. Point flywheel to 0 degrees with #1 @ TDC. Your distributor should be pointing to the #1 plug. If all this is true, you are done with spark. Move on to compression test. If someone has pulled the distributor, it might be put in 180 degrees out of time, or the wires are plugged into the distributor cap in the wrong places.

Suggestions on scope use. There are special insulation piercing probes that will work much better than pulling major connectors apart and risking damage. However, a paper clip usually can be used to back probe a connector. When you have your massive connectors apart, be sure to spray them with contact cleaner and use the dielectric grease you always have handy. See how easy this process can be?

BTW, what kind of scope did you get.?
Lazarus
 
I bought a cheap unit branded Hantek 1008B, but it has a lot of good features I am still learning the generator mode, the unit came up with a lot of alligator clips and small bag of connectors you can screw onto, also got me some 0.7 mm test probes, It is a 8 channel paid less than $100 and installed it on Win 10 Pro Laptop although my Vida is on a different Win XP laptop, I might try installing it on XP as well - takes only few minutes.
Regarding spark- it is solid you could see it in the mirror in the engine compartment on the Video, there is a spark tester attached to the pug, and on the windshield there is the Noid light
at first crank the Noid light is brighter, afterwards pulse gets dimmed by little, but the spark is no longer an issue, At this time I am suspecting water in the gas as the night before my car went down there was a heavy downpour( back in November), so my next days off I will be removing the injectors, cleaning them and will drain the gas tank or attach another pump to the injector rail.
Gas flow is strong at the return line and I swapped few FPR's so it is either bad gas or clogged injectors and bad gas. I wonder if rain water could get in the tank from somewhere?
 
Wright, just like the loan mower:urgod:, took off the intercooler elbow at the TB and sprayed, had 1/4 can left and towards the end it started firing!!! Bought a new can but my helper is at school and will try it in the evening again. I held the TB fully open BK cleaner should work the same?
 
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