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Volvo 740T no-start problem

missthe1122

Member
Joined
Feb 16, 2011
Location
Long Island, New York
I know 740 turbo no start is an old much addressed topic so I apologize in advance. I believe I've tried all the advice that I could find on this forum and others before posting this. Anyway, I just bought a 1990 740 Volvo turbo wagon, LH 2.4. It ran great when I drove it home (about 27 miles). But the next day, while I was driving it just stalled. There was no indication of anything going wrong, it just stalled and then would not start. I checked the spark and it was present. I pulled a plug and no smell of gas. The timing belt looked good, but it wasn't very tense so I thought maybe it skipped a tooth or two. So I towed it home, charged the battery, replaced the timing belt, tensioner and water pump, spark plugs, ignition power stage module and crank position sensor. (I had the parts and planned to do all this anyway). There's a good spark, the engine cranks fine, but it wouldn't start. I Checked diagnostics and got 1-1-1. However, when I triggered the fuel injection test mode (plug inserted in pos. 2 and 3 presses of button), I heard relays click, but no fuel injector action. Per on-line advice, I replaced the RS relay and the fuel pump relay. I heard the fuel pump running with key turned to position 2. I verified plenty of fuel pressure on injection rail. I verified the grounds on intake manifold and valve cover to chassis. I measured 12V at the ballast resistor pack and each individual injector harness. It seems that the injectors aren't getting ground signals from the ECU. I was advised that I should replace the computer. I'm skeptical because the computer reports codes and also invokes the fuel injection diagnostics. I'm doubtful that a bad computer could do these things. Before I go ahead and buy a computer, is there anything I may have missed that could prevent the computer from sending ground to the injectors? Or, is there anything at all that I could be overlooking?
 
Hi ZVOLV. I narrowed it down to injectors not triggered. Spark. Fuel Pump. Fuel Pressure. Engine compression all checked out. 12v present at injectors. Seems to come down to ECU not sending ground. I was just wondering if any other condition would stop ECU from triggering injectors, besides it being bad. The diagnostics work. Fuel system test triggers everything but injectors. I didn't want to buy a computer until I could be sure that's the problem. RS relay, fuel pump relay brand new. Pump works. Pressure at the fuel rail. Grounds are good. Couldn't think of anything else.
 
12v may be there but not enough current. Have you tried a noid light or test light?

Resistor pack on left inner fender for the injectors. The wiring cab go bad. Same with injector relay on left strut tower. ECU is possible, but check both the power and control side of the circuit first. Meh, or swap ecu if you have one. Whichever is FASTEST!
 
I used a multimeter to test voltage. Thing is I stupidly bought what I thought was a 740T ECU on eBay - and it turns out to be for a LH2.2 system, even though it was listed as being for a 1990 740T (the last 3 digits 541). I'll have to eat that one, and find the right ECU. I have a 560 ECU in the car. Should have checked before leaping. I saw the perfect replacement in the FOR SALE section, but of course it was sold already. I ordered a bosch noid light on eBay. Is there a way to confirm that the ECU is pulsing the injectors?
 
My formal training and experience has trained me to use a test light. I have found circuits that have 12v on a meter, but not enough current to operate the unit.

Noid light is a plug n play way to confirm voth your power side of your injector circuit is good and the negative control side (ecu) it also confirms proper current.

A test light could also be used between the two injector wires. First, hook it between ground and injector positive. Key on. Light up? Then between injector pos wore and injector negative wire. Crank. Blink? Noid light does the same, but it just clips in.
 
Okay. I do have a test light. It's weird. I slapped the passenger side of the center console, then cranked the car and it fired once, then no start again and I couldn't repeat this. I hate electrical problems, but I'll follow your advice. Looking for another ECU right now.
 
Yes. 1-1-1 with plug in #6. With plug in #2 and three button presses. IAC and other relays click but no 'fast click' from fuel injectors. Did the same test with my 240 and the fuel injectors clicked away. Got the bosch noid light. no flash on injectors. The computer is actually the 563. But I can't believe that the computer could be bad, if I can trigger diagnostics. I replaced the RSR relay and the fuel pump relay in the center console. Fuel pump works. I did get rather high fuel pressure on the rail, more than 41 PSI. I will change the regulator. Could high fuerl pressure stop the injectors from firing?
 
"No way!"

Do basic electrical diag with a test light. Do you have spark?

Crank sensor dead I water would cause a no spark and no injector pulse.
 
Thanks for your help. ZVOLV. Sorry for the delay in response. You were right about using a test light. I can measure voltage but no light on injectors. Have a great spark. New IGN module, RPM sensor, plugs installed. Problem is fuel injection. Installed turbo ECU in my 240. It started, although didn't run very good (rich and no idle). Put 240 ECU in the 740. Same results. No injection. What did you mean by LH relay? I replaced the RSR and the fuel pump relay. Is there another relay involved? I know my 240 has a relay on the Ignition computer housing. But, didn't see one on the 740. Didn't see the ign computer for that matter.
 
I finally found the problem - and it's a lesson in "think simple" for me. The connectors between the ballast resistor pack, the RS Relay output and the injectors were all highly oxidized to the point of dropping the voltage or current to the injectors - so no injection. This car hadn't been driven in about five years before i bought it. I should have known better, but I got a false confidence from the fact that I was able to add some gas, start the car and drive it home. I bought a RS relay, fuel pump relay, ignition module, RPM sensor - all of which was unnecessary. Lesson to self. CHECK THE CONNECTIONS FIRST!
 
Woot!

$5 test light, wiring diagram, and some poking around woulda been cheaper, right!?

So it runs?
 
Hell Yes!!! Starts right up and idles and accelerates nicely. Now I have a noid light set and good spare parts, LOL. Now I have a big sister to my 240. The same color red. It needs some cosmetic work, but the summer's finally showing it's face in this neck of the woods. Thanks again. ZVOLV.
 
You have experienced "fretting". Temperature change, moisture, and vibration can cause microns of fretting. I "fixed" a circuit yesterday by removing dusty fuses, inspecting, then reinstalling them, and then the circuit worked.

OT: I like the horseshoe crabs in Long Island.
 
I live on the water on the south shore. My backyard is a dock to a canal. No horseshoe crabs but if I throw a crab trap off my dock baited with a chicken I can quickly catch a few dozen blue claw crabs. Good eating! My neighbors call me sarcastically the "Volvo whisperer" because I have five old Volvo's parked around my house. 1990 745T, 1992 960, 1990 240, 1992 240 and my daily driver 2000 V40. LOL..
volvos.jpg
 
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