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Diagnosing No-Starts on Some 740/940 Volvos

 Use this step-by-step guide to track down the
most likely suspects for no-starts on your 740/940 Volvo.


 

 

When you don't know what you're doing, you can create a MESS, like I did chasing after red herrings!

Instead, download my step-by-step guide to help you track down a likely suspect for your no-start.

 

 

 

 

 

Learn from my mistakes!




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Addendum1: Ignition "On," battery warning light is off. (Following is from memory, so I'm not sure if it is correct). When cranking and engine does not start, battery warning light is on. Symptoms imply a faulty alternator or connections to it. In my case, one of the brushes had become stuck in the up position, so that it was not contacting the slip ring. If your alternator does not work, no current is fed to the fuel injection system and your engine will not start.

Addendum2: One of my readers, Cameron Mael, has found a fault with my diagnosis. And he is right! When conducting the spark test, he suggests first testing the spark plug wire (#1 is standard) rather than the coil high tension wire from the distributor. Why? Because if there is something wrong with the distributor rotor or cap, there is no current sent to the spark plugs. If there is no spark at the spark plug wire and there is spark using the high tension wire, then the problem is in the rotor or cap. Well done, Cameron! Thanks. [One way to test for spark at the spark plug wire is to pull the #1 plug, plug it into the #1 spark plug wire, lay the metal side of the plug against the engine block, and have an assistant crank the engine. (Use a plastic grip or salad tongs to hold the spark plug against the engine.) Look for spark at the spark plug gap. I have not yet instituted these instructions into the guide.]

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 There are many possible causes for a no-start. While not exhaustive, this manual covers the most likely suspects right up to the fuel system Electronic Control Unit (ECU) and ignition Electronic Control Unit (IECU), where my expertise ends. Having chased many red herrings (and needlessly spent money) as a do-it-yourselfer, I now adhere to the motto: “Be informed. Check twice, buy once.”

Diagnosis is done without the use of fault codes or an oscilloscope. How so? In the end, a computer delivers certain voltage or current values to components under certain conditions, and a lot can be discerned by testing for those end results.

My Volvo is a 1987 740 turbo, B230FT, L-H Jetronic 2.2, EZ 117K ignition, manual transmission. So, instructions are mainly for this model, but advice here may help you with other models and variations. Exceptional wiring diagrams are available for different fuel injection and ignition systems at www.autoelectric.ru/auto/volvo/740/1989/740-89.htm for the 740 and www.autoelectric.ru/auto/volvo/940/1993/940-93.htm for the 940. Refer back to these schematics as the standard. (Oh, and one thing, the wires for the EZ117K Ignition System, B230FT, are reversed for #1 and #3 terminals on 5, the distributor (Hall sensor). #1 lead is black, #3 lead is red.)

A dead engine has three possible culprits: mechanical, electrical, or fuel.

1. No or little noise on ignition “Start” (engine does not turn over or crank) or grinding screech. Check for 12 volts DC at battery terminals (note: a faulty battery will quickly drop to 9-10 volts when under load). Also clean battery cable ends and battery posts. Other possibilities are the starter solenoid and starter (grinding screech) and ignition switch and circuit.

2. Engine cranks but doesn’t run on ignition “Start”—the symptom for all following tests. Be sure you have gas (and not water; I once had that problem!). Then check that fuse 1 (main fuel pump and fuel injection system) is intact.

 
Figure 1. Test for spark. Pull coil high tension wire from distributor. Use plastic grip to hold end 1/8” from metal on engine block while assistant cranks engine. Don’t overdo cranking.

3. Mechanical. Check timing belt. Lift oil filler cap to view overhead camshaft while an assistant cranks engine. If camshaft rotates, the timing belt is fine. If the camshaft doesn’t rotate, your timing belt is likely broken.

4. Electrical. Pull the coil high tension wire from the distributor and hold its end about 1/8” from metal on the engine block (Figure 1). (Danger! Use a plastic grip or tongs, never “insulated” metal pliers or your bare hand! Perform test in dry environment.) With someone cranking the engine for 2-3 seconds, check for good spark. (Don’t overdo cranking, as some manuals warn it could damage sensitive electronics.) If no spark, go to Step 4a. If good spark is present, go to Step 5a.

 4a. No spark. In olden days, no spark from the ignition coil usually meant it was faulty or the coil primary contacts “1” and “15” were corroded. These days, other possible culprits include the Hall sensor or Power Stage—and they cannot be discounted. With ignition “On,” check for 12 volts DC at the primary lead of the coil (between “15” and ground—see Figure 2). If no 12 volts, trace back in ignition circuit. Also check . . . . (continued in booklet)



 
Figure 2. Check for 12 volts DC between “15” terminal on ignition coil and ground with ignition “On.” (Ground is sanded bare metal on hood hinge.) 12 volts between “1” and ground implies that the primary winding is fine.

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(Note: This guide addresses a dead engine—not one that sometimes runs. It is much harder to isolate the cause for the latter, but conditions are constant for the former. )

 

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