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Engine cutting out at speed

My car has started to cut out at speeds of 70 mph. For some time have just been doing small runs around London but on a recent roadtrip the engine cut out a number of times on the motorway. This usually happens after 100 miles or so. 3 mechanics have looked it over and can’t find anything wrong. It’s had a major service and the carb has been cleaned. No reports of problems with the fuel pump. Also sometimes idling is slightly rough and can dip low. On 2 occasions have had problems starting and have lifted the bonnet and checked the seating of leads and spark plugs and distributor cap and then ‘banged’ the bonnet shut and it starts!! Could it be electrical? Some views include - distributor cap (hairline crack), rotar arm, coil or the leads to the plugs. Can you help?

How about checking the fuel pump?

Any of many electrical connections could be bad.

You say no reported problems with fuel pump? How do you know? The thing is fuel pumps fail when they are hot, and that takes a while when they are located in the fuel tank which keeps them cool. the symtoms you describe could be fuel pump failure.
On the other hand wiggling the wires and then having the engine start up could mean a poor wiring connection, so wiggle one wire at a time, and then try to start. That way you may be able to narrow down which lead is bad or loose.

Even if your fuel pump works fine at idle and lower speeds, it may not be able to deliver the volume of fuel you need at higher speeds.

What year 323, do you really have a carb?

I’m pretty sure it’s not the fuel pump because 3 different breakdown guys checked it over thoroughly, one replaced the fuel cap and all reported no faults. They said gas is pumping through fine. On the whole it starts like a dream, runs for 150 miles or so like a dream and then the tacho dips suddenly and engine lights come on. I also had a full service on it 2 weeks ago and no faults reported.

So, we have a 323 of unknown vintage with a carb.

Yes, it could be electrical. There are a number components in the ignition system that can become heat sensitive with age, the two most common being the coil and the igniter. Since my just-done Mazda 323 history in Europe search says the badge goes back to 1963, this could even be a point-based ignition, which would also mean the points and/or condensor could be toast. I know you said it’s had “major servicing” but I have no way of knowing exactly how “major”.

When you checked the distributor cap, did you check the contact points on the cap (where the rotor send the pulse)? If there material transfer, carbon deposition, or material irregularities (wear on the metal)?

If, in fact, the rotor, cap, wires, and plugs have all been changed, my next guess would be the coil. Coil windings are insulated with a varnish-like coating that can crack over time from thermal stressing and short windings out. One way to test this theory is to get a spark tester and when it fails check for spark loss.

Post back with how you made out.

Thanks for your advice. After sending this the car then developed a more persistent problem. It wouldn’t start at all. Which in some ways was good news. So after some testing etc have had the coil replaced and still wouldn’t start. Had the distributor tested and no problems there. According to my mechanic who is being extremely helpful but is baffled there is no spark and he thinks it is electrical. Any thoughts?

How was the distributor tested? You say there’s no spark, did the shop actually check for spark? Additionally, since I know that in GB there are some terms that we here in the U.S. use differently, I want to be sure we’re clear. When you say “no spark” are you saying that the spark plug has been looked at (physically or with a scope or a timing light) and there’s no actual arc between the electrodes, or do you mean that the cylinders are not firing?

If there’s no arc, then the year of the car will help us.

If it’s an old points-based system the shop may want to check for voltage at the coil primary. Every time the points close they complete the coil primary circuit and every time they open they interrupt it, causing the field in the coil to collapse and induce the voltage spike.

A later igniter based system operates very similarly, except it controls the circuit of the coil primary using a sensor instead of points. See the attached link.

NOTE: in either case the voltage at the coil primary will be a square wave. The absolute best way to check a square wave is with a scope. By using a meter you simply get some average of the voltage when the circuit is closed and when it’s open. It really does not tell you as much.

If by “no spark” you mean that the cylinders aren’t firing, then the fuel system becomes suspect. A pressure check at the line could be a good idea.

Post back.

Thank you for your advice and your patience.

The distributor was removed and tested at the car repair shop and found to have no fault.

Previous to testing the distributor a new coil was fitted but the engine still wouldn’t start. New spark plugs were fitted 3 weeks or so ago (along with a full service) when I was having the problem with engine cutting out at speed and then on occasion not starting.

It is an old points based system I think. When the AA came out on one of the occasions when I broke down they removed the distributor cap and cleaned the points removing carbon like deposits. On the second (of 3 occasions of engine cutting out) the breakdown guy checked the fuel pump (he actually sucked the fule from the pipe!!) and said it was ok and that he would ‘put his name on it that it was working fine’.

On a different occasion another guy wrote on the breakdown report ‘suspect HT system’. My mechanic is saying there is no point in replacing leads etc because there is no spark! Will clarify this with him.

The first year of registration is June 1990 here in UK as new - a 323 SE Executive 4 door saloon 1598 CC. I still have the manual but it’s not much help beyond basics.

Can I ask when you say igniter do you mean the ignition switch? The manual also mentions when the engine won’t start to inspect cable connections to starter and solenoid. Any thoughts? I love my car and I will go the extra mile to fix it but when it’s this old you just don’t know when it’s best to cut your losses!


Nope, I did not mean the ignition switch. The igniter I was referring to replaced the points system to turn the coil primary circuit on and off. Since yours is points-based, you have no igniter.

Your symptoms don’t point to a starter solenoid. If the starter solenoid were bad or its connections poor it would not affect the car once started and would not cause cutting out on the highway. YOu can safely rule this out as a possible cause.

If your points were fried (carbon deposits) both the points and the condenser should have been changed. The condenser is a capacitor mounted in parallel with the points that keep the points from keeping an electrical charge, that charge which when discharged by the points closing causes arcing and carbon deposits, as wel as point material transfer. The distributor cap should also be changed, as carbon leavse traces that can become resistive shorts to ground.

Testing the fuel pump means putting a pressure gage on the supply line and checking for proper pressure. However, since this is carbed it’s a 2-second check to see that the float bowl is full and the accelerator upm operating. It simply involves propping the choke open, looking downg the carb’s throat, and twisting the throttle linkage. A spray of gas should shoot into the carb’s throat. I know you said the carb’s been cleaned, but if the float were hung up the needle valve could be staying closed and preventing gas from getting into the float bowl.

This problem is not the type of problem that signals the end of a car’s useful life. Any decent tech should have no problem finding out why you have no spark.

I do think you need to clarify this HT comment. I’m unfamiliar with the term, but if he’s using it to describe the secondary ignition system (and it sounds like he is), then if he’s verified no spark I’m puzzled as to why he’s unable to troubleshoot further. The system is pretty simple. When the points close, 12VDC is allowed to flow through the coil primary (the windings). When the points open, the circuit is broken, the magnetic field in the coil collapes, and a high voltage spike is induced into the coil core by the collapsing field. Lack of spark means either no primary voltage, the coil itself defective (read: shorted windings), the field isn’t collapsing (perhaps a short between the windings and ground or a short to ground at the points), of the induced voltage spike is shorting to ground somehow before it gets distributed. See my comment above re: the distributor cap and carbon trails.

So it gets odder and odder. The car started today after further attention to the coil and distributor. I’m not sure what was done (and don’t like to ask too much) but it was running and the mechanic drove it round the block. On return as he was about to explain to me what he had done it cut out, restarted, ran for 30 seconds and cut out and so on. The alternator was checked and full strong signal is present. After further checking of leads etc it started and ran without a problem. Only thing is that now the fan won’t kick in. Engine runs beautifully but no fan and so it starts to overheat. The revs also no longer work.

I went on the Mazda Enthusiasts Website and identified someone with exactly the same problem that I had originally i.e. engine cuts out at speed and also trouble starting when this happens and on other occasions. To begin with the problem manifested that after a good long run when it cut out I could restart but could go no more than a mile or so and it will cut out again and so on. This is particularly the case after it’s been driven for a couple of hours. The revs keep diving to 0 and that’s it. The advice given to this individual with a similar problem if I have remembered correctly was that it could be coolant temperature sensor or the oxygen sensor. I understand the former can be tested but the latter can’t.

I think the reference to HT should be HD but I write it down as was written on the breakdown report. I took it to mean the leads from plugs to distributor cap etc. None of the leads or d.cap or rotar arm have yet been replaced. My mechanic is saying let’s identify the problem if we can before we change anything else and so save money. Thank heavens.

Any thoughts on the situation now?


This one is definitely getting odd.

I’m still uncomfortable with leaving the points, condenser, rotor, and distributor cap on after having found the points to be fried, but I can’t criticise the philosophy of diagnosing before changing parts. But, these being inexpensive normal tuneup parts anyway, I’d chenge them.

I’d be inclined to suspect the carburator. Specifically, the float and/or its associated parts (linkage and needle valve). This “cutting in and out” is typical of an old carb that can’t seem to keep the float bowl properly filled, acting like a very sticky valve. Perhaps one of the others here can suggest a way to check for this without opening the bowl (removing the top of the carb) but I don’t know of any.

By “the revs” do you mean the tachometer? This in conjunction with the fan suddeny not working suggests that perhaps you have a few fuses blown. Perhaps in working the problem the tech accidently sent a spike through the bussline.

If the fuses are good, you have two simple fan items to check besides the fan itself, the temp sensor and the fan relay. The fan and these components area easy to check with a simple voltmeter and a schematic. The shop should be able ot check these out.

Your comments on the carb are interesting because each time I broke down the breakdown guys opened it up and applied carb cleaner then applied vigorous suction to it. Each time it then ran ok for a distance. Also the revs seemed temperamental riding higher each time (in between breakdowns) after a period of further driving. On one journey if the revs went past 3 on the tacho (if I drove faster than 50 miles an hour) that’s when it had a tendency to dive to 0 and cut out. On one stretch of road I managed a distance of 40 miles keeping below 50 mph but then one of my passengers needed a break. I stopped and when I tried to start it again it just kept cutting out. Another breakdown guy, and another carb clean later and I managed to finish the journey which was another 70 miles and no problems.

I did mean the tachometer but the fuses were checked and no problem found there. Also if the carb is the problem would’nt it keep cutting out anyway? Strange that the engine started running with no cut out at all but then the fan and tachometer are now out. It’s off to the shop so will let you know. Will do the other parts also.

Sorry to not have a definitive answer…but…my I recommend that you switch to electronic ignition? It’s much more reliable and efficient than points ignition.

In many ways I agree with ‘mountainbike’…except that you say wiggling wires and slamming the bonnet has straightened it out in the past. Those things wouldn’t effect a carburetor, I wouldn’t think.

Good luck!