hard to start: intermittent spark?

[frustrated]

My VP (series II, V6) has trouble starting. It cranks for perhaps 5 seconds or more, and then splutters into life. It may take one to three attempts, and there is an occasional backfire during the process. Once started, it appears to run fine, and it will be easy to start again until left off for an hour or so.

I think the problem is electrical, since I've put a strobe light on a spark plug lead, and can see that the spark is missing then intermittent during the initial cranking. And when the engine has started, I see the occasional missing spark until things have warmed up.

In attempts to fix the problem I have replaced the spark plugs, and the CAS (crank angle sensor) with no effect. The coils measure 6K on the output and 0.4 ohms on the input, as expected. The spark plug leads have the correct resistance. the DFI (direct fuel injection) module connector is clean, and has good contact resistance to the CAS plug. The battery is fully charged and cranks the engine vigorously. It would be interesting to measure the positive voltage to the DFI during cranking, but I can't think of an easy way of accessing the pins.

Any ideas?!?!? I'm stumped. I've searched the forums, but can't find the solution.

Prior to realising the apparent electrical nature of the fault, I had cleaned the injectors, cleaned (and then replaced) the IAC valve, cleaned the throttle body, and replaced the petrol filter. All with no effect.

After a recent long trip on the highway at 100 kph, the car started perfectly for a few days, and then gradually deteriorated. It is definitely getting worse with time.

Cheers, Michael (alias "frustrated")

[Not_An_Abba_Fan]

I'd be looking at the fuel pump. If it was on the way out it will give similar symptoms.

[michaelw]

DFI module? My VN went through one every 3 years or so.

Naturally it didn't fail all at once. First the car got harder to start then later on it just would die whilst driving.

Mike

[frustrated]

Thanks guys for the feedback.

I think the fuel pump is OK. In any case it couldn't cause a missing spark.

I have a VT Commodore as well as the VP. If the DFI modules are interchangeable I could swap them over. Does anyone know? They look identical as far as I can see.

Probably unrelated, but the car also has problems overheating under load on hot days.

Michael

[michaelw]

I am pretty sure the module will swap but check with someone else first.

Mike

[frustrated]

I bit the bullet and bought a new DFI module ($160 from Auto 1) and new spark plug leads ($50). I read somewhere that poor leads can kill DFI modules, so I wasn't going to take a chance with the existing leads.

The car started first go, and the sparks (as measured with a strobe timing light (left over from the days when I had car with a distributor ) were there from the beginning with no missing pulses.

If you don't hear from me otherwise on this thread, you can assume that the problem is fixed

Incidentally, you would think that missing sparks is something that the engine management computer could keep track of, and give you an error code. Assuming that this information is available from the DFI module.

Michael

[lux]

i have series one vn dfi went had a look @ vt one they bolt up different end up using vp one

[frustrated]

OK, the problem is back, same as before. This is very depressing.

For a day after replacing the DFI module and spark plug cables the car was starting instantly, every time, even after being left overnight. It hasn't done this for months, so I was very confident that I had fixed the problem.

Then this afternoon the dreaded 5-10sec crank followed by a spluttering start was back again. This happened several times over the next hour or so. Lots of smoke out the tailpipe for a while after the start, which I presume means that fuel was being injected, but just wasn't being ignited, presumably due to a missing spark. I haven't put the timing light back on yet to see if the sparks are missing.

One possibility that occurred to me is that when I had the battery disconnected to install the DFI module, this reset the ECU (electronic control unit), and things worked for a while until the ECU recalibrated itself, possibly due to a malfunctioning sensor. I know this is clutching at straws. No error codes show up.

[michaelw]

Check the connector and all the wires to the DFI. When the engine is running smoothly give the cable a wobble.

Mike

ps sorry for streering you crook, but my car it was the dfi. And you'll always find a use for one somewhere down the track.

[frustrated]

Thanks Mike. No worries about the DFI issue, I had convinced myself to replace it anyway!

I will do some more exploring with the timing light, wiggling connectors, and so on. I should check all the sensors (MAT, MAP, O2, etc) as well.

[Boonz]

fuel pump strainer blocked??? can cause long cranking periods

[krzyvs]

i am having the same problem with my vp at the moment, im starting to go through the process of elimination, one thing i noticed with this car in particular is the fuel pump seems to keep running about 15secs after the motor has been stopped im not sure if this is a normal feature as i never noticed it with my other commos, which has led me to thinking of over supply of fuel.. its just a thought.

[pow3rslave]

problem with swapping out dfi is that it can equially be dfi or coil pack, and you only find out which when you swap one (sometimes the wrong one )
i'd also be looking at injectors. an injector that leaks overnight into the cylinder could cause flooding of sorts, it'd cause the exhaust spluttering and would possibly foul plugs meaning they'd be working less.

[frustrated]

Peanuts Inc - thanks for the pointer to the fuel pump strainer. I might have to remove the pump and have a look if the problem persists.

krzyvs - my fuel pump also runs on for a short time after turning off the engine.

pow3rslave - I checked the coil packs as much as I could before buying the DFI by measuring their primary and secondary resistances. They checked out OK.

As regards injectors leaking, without having a fuel pressure gauge, is there any easy way to determine if this is happening?

Meanwhile the car started perfectly this morning.

This sure is an annoying problem.

[pow3rslave]

i think there'd be evidence on the plugs, but i can't remember what it is. it's either grimey black crap, or dusty tan crap. basically if there's any crap on your plugs and their not ancient you could investigate the cause.

[88GreenVN]

Have you tried a different ECU? - I would.

[frustrated]

88GreenVN - no I haven't tried a different ECU, that sounds like an expensive option. I guess an ECU from a wrecker would be OK, but I can't imagine it would be cheap.

Meanwhile, the car mostly starts immediately, but occasionally requires a 5-10 second crank. I reckon that I must have at least two simultaneous problems: there was definitely an intermittent spark problem before, which has been fixed with the new DFI module. I'm now looking at an injector leak. Is there any way of determining this, or should I just take out the injectors and get them tested?

[Aside: my radiator developed a serious leak earlier in the week - $460 quoted for a new one from Holden, $160 for a new one from a radiator specialist; hopefully this will fix my overheating problem. And the tail pipe fell off the rear muffler the week before! I've strung it back together with wire until I work out where to buy a muffler.]

[RockyVX]

you can get a radiator from the wreckers for around the 60 mark. I have heard of the ECU's going for as little as 15 on Egay.

Take the injectors out and get them flow tested. it cost me 10 to get them all checked out in Rockhampton, but ring around a few places and see if you can find the place that does them, without doing any mechanic work, or they will probally shaft you nice and proper! At the same time, they can replace the collars on the injectors for a few gold coins (i needed 3 courtesy of a previously careless screwdriver)

Also check the earth strap between the engine and the chassis. also the CCA of your battery!

I hope this helps

[frustrated]

RockyVX - thanks for those pointers. I should have thought about Ebay before.

One interesting thing about radiators: the installation instructions that came with it said to measure the voltage of the coolant, since apparently some electrical faults can cause current to flow through the coolant back to the chassis of the vehicle. This causes electrolysis in the radiator, and a short life.
I haven't made this measurement yet... must do so this weekend.

My earth strap is OK, and the battery cranks the engine very strongly.

[RockyVX]

for the radiator, run a length of electrical wire (12v) from a self tapper stuck in one of the flanges on the side of the radiator, and the other end into the chassis.

No need for beefy cable. The thin stuff will do the trick. Im talking normal 12V 5a wire

edit : forgot to add - two apparent causes - (1) stray currents within the engine, and (2) stray current from thermo fan wiring.

[frustrated]

OK, it looks like the problem is finally fixed!

And the cause was (drum roll...) either the fuel pressure regulator or the fuel pump. I replaced both, and now the car roars into life within a second just like new.

Earlier I had replaced the ECU, no difference.

Then I took the injectors out, thinking I would get them cleaned and inspected for leaks. A couple of places I took them to couldn't do the job on the timescale I needed, and one mechanic said "I've never had a problem with leaky injectors, they typically last 400K without a problem - you should check the fuel pressure regulator, I replace those all the time."

The fuel pressure regulator is the device on the output (driver's side) of the fuel rail. It is vacuum operated, so that when the engine is off, the valve is closed, and fuel pressure is maintained in the fuel rail. Ergo, if the valve leaks, the pressure can drop, and it will be hard to start the car from cold. The mechanic said to check the vacuum hose for the presence of fuel. I did, and sure enough there were evidence of damage to the hose from fuel leaks (although I didn't see any actual fuel at the time).

So, I went to Auto One and bought the Bosch part for $99. Shoved it in, and then the damn car would sputter for a while and stop, giving all the signs of fuel starvation! What on earth was going on? I had at least 15 litres of fuel in the tank, and the gauge was showing a couple of notches above empty. I took off the fuel rail (leaving the injectors and all hoses attached) and verified that fuel was coming out of the injectors when I cranked the engine.

All I could think of was that the fuel pump had finally given up the ghost, so back to Auto One and $129 for a Bosch replacement (looks nice, no pulsator unit). Then to drain the 15 litres of fuel in the tank, and replace the pump, which was fairly messy with all the petrol around, but wasn't too difficult and took about 1.5 hours. Incidentally, Auto One told me that they sell tons of fuel pumps and quite a few pressure regulators, but no injectors.

I poured the fuel back in, plus another 3 litres I had in a container, and ... the car still didn't get beyond a splutter! Arrggggh

The only possibility I could think of was that there _still_ wasn't enough fuel in the tank, due perhaps to the car being on my driveway, sloped at about 15 degrees, nose down. I got another 10 litres from the service station, and this did the trick. The car has started instantly first time ever since. It is definitely (cross fingers) fixed this time!

So I don't know whether the problem was caused by the fuel pressure regulator or the pump. I'm inclined to blame the regulator since (1) it was definitely faulty, as evidenced by the damage to the vacuum hose, and (2) I have heard people claim that fuel pumps tend to go bad very rapidly, and my problem has been fairly consistent for almost a year.

A take away message from all this is: if you have cold starting problems, have a look at the vacuum hose from the fuel pressure regulator. The pressure regulator is much more likely to be the problem than the injectors. In retrospect the fuel pressure regulator is an obvious thing to check, but it wasn't listed in my Gregory's manual in the "hard to start" section, so I didn't suspect it.

Wouldn't it be great if something like Gregory's could be updated easily from the experience of mechanics and auto-electricians? The official manuals from Holden aren't all that useful - plug in your Tech2 diagnostic tool, if it fails test 63, replace engine

[Not_An_Abba_Fan]

Look at post #2....

[frustrated]

Yeah, yeah, I know!

Still, it might have been the fuel pressure regulator, and the pump may have been OK?

The reason I didn't go after the pump initially is that I couldn't think of an easy way of testing it. The manuals talk about using a fuel pressure gauge, but I don't have one (and they cost a mint). In fact, I reckon you can probably measure the fuel pressure by how easy it is to compress the rubber pipe on the inlet to the fuel rail. It may even be possible to calibrate this somehow.

Anyway, next time I'll take your advice!