Starting problems

[AliK]

Fellas,

I need your experienced heads on pls. My z has been pretty good at starting from cold but recently over the last two to three months she needs a LOT of cranking but eventually catches. In fact so much cranking that by the time she catches, the oil pressure is half way up on he gauge!!!

When she eventually gets going it sounds like firing on half or four cycls for a few seconds until the rest come to life and she misses a little for about a minute until warm.

I suspected electrical, so have replaced plugs, cap and rotar arm on the 280zx dizzy.

The coil is really not that old. I may try to replace that with a spare one but somehow I have this feeling it won't make much of a difference given the rest of the time it works impeccably. Except for checking resistance, any tips on checking coil health which does not involve my tongue and HT leads!?

I've checked the timing and it's still at 10 degrees.

My next suspect is fuelling. I changed the fuel filter pre Japfest (with a clear one to see any rust etc in the future) and she revs out perfectly, so I'm not convinced it's lack of supply. Could it be too lean that causes this? In which case why would it deteriorate over time?

Compressions range anywhere from 160 - 172 which is still consistent with what I had the day after the head build. Bizarrely before Fourways rebuild the head the compression was in the mid 170s to 180s (see the pic), doesn't make sense why it's dropped post rebuild but that's a different discussion. (FYI Cyl 1 was found to have a completely loose valve seat)

So any thoughts? Anyone seen this before?

 

[Rob Gaskin]

I don't know when you took those plugs out i.e. after a run or after trying to start it etc but 3 - 6 are the wrong colour. They are either oily or the mixture is too rich.

Compression variations are just on the limit IMO.

Strangely the cylinder with the lowest compression seems to be running best.

Valve clearances - have they been checked since the rebuild?

Plugs - standard recommendation?

 

[AliK]

Spot on Rob on the plugs. The photo is also pre the z-therapy carbs so I'm sure the mix was all over the place. Plugs were taken out after idling to park the car in the garage.

I just don't get how I had better compression before the rebuild using the same gauge and the same battery charger booster to make sure cracking as strongly.

Valve clearances not checked - that probably also explains why it sounds a little "tappety". Must dig out that Haynes manual and the feeler gauges I haven't touched in a decade!

Plugs are totally standard NGKs.

 

[toopy]

With regards the cold starts, have you checked for proper operation of both the chokes?

 

[AliK]

Check! I did indeed sir.

 

[SacCyclone]

Have you also checked to see that the main jets at the bottom of the carbs returns to the "up" position when the choke to taken off. If you have stock SU's, the main jets have a tendency to stick after the choke is taken off causing a very rich burn and all kinds of sputtering. This happens in older carbs especially.

 

[grolls]

Link for coil resistance. check quality of spark at the plugs and check choke working correctly.

http://zclub.net/forum/showthread.php?t=3028

 

[jonbills]

Some possible reasons why compression might go down after a rebuild:
Chambers opened out or
Thicker gasket used or
Rebuilt valves not actually sealing or
You did the test different.

Have you pulled the plugs recently? They'll tell you what's going on.

Does it smoke when it does start?

 

[Rob Gaskin]

Ali, if you run the car one day and start it the next does it start well?

I'm asking because I started both my Zs last week after a long break. Both took a lot of starting and this was anticipated so I charged the batteries well and also 'jumped' them with a spare.

The car I went to Silverstone in took a lot of starting mainly due to having a mechanical fuel pump but the car with the electric pump was not brilliant either and took some coaxing into life from a couple of cylinders and then gradually 6.

On Sunday morning (very cold and damp, car outside all night) the car started immediately. Both will always start really well if used recently - even from cold. No problem.

 

[Farmer42]

Had the same problem on cold starting earlier on in the year. I swapped out the standard NGK BPR5ES spark plugs for BPR6ES which run slightly hotter and give a stronger spark. That did the trick & it starts a lot better when using the choke. If you have the former, it may be worth a try.

The only thing is that you may need to adjust either the mixture or the timing to avoid pinking when it does warm up.

 

[jonbills]

I suspect you fixed your problem just by having new plugs, rather than a change of temp rating.
btw, I'm pretty sure NGK 6 is the OEM plug temp rating and 6 is colder than 5.

This diagram is good:
https://www.ngk.de/en/technology-in-detail/spark-plugs/thermal-behaviour/the-heat-rating/
it shows that a warm plug like a 5 only needs to be lightly loaded to be in the right operating temp range, and if spanked, will overheat and cause glow ignition.
Whereas a colder plug, like a 7, needs to be driven hard to get into the optimal zone. It won't over heat, but it might foul if you just pootle about in a low compression/low load engine.

 

[SacCyclone]

What Rob Gaskin said, Zeds always need coaxing to start after sitting several days. Been my experience anyway with many Zeds that I have had.

 

[MaximG]

With a 280zx dizzy you should be running BPR6ES - 11, as recommended my Mike Feeney. The 11 denotes the plug gap which I think is 1.1mm but might need to clarify that.

 

[Farmer42]

I suspect you fixed your problem just by having new plugs, rather than a change of temp rating.
btw, I'm pretty sure NGK 6 is the OEM plug temp rating and 6 is colder than 5.

You're right. I did it the other way round & now have 5s in place. Whatever they are, it did improve the starting although it still takes a couple of turns to fire. It's not straight away.

 

[johnymd]

My black car will start and tickover immediately you touch the key if you start it every couple of days. It's the easiest starting car I've ever known. If I leave it a few weeks it a totally different story. Takes several rotations before it fires.

 

[jonbills]

I think cars with mechanical fuel pumps and small float chambers are going to need a few cranks before they fire after standing a few weeks. I imagine evaporation or leaks will make the float level too low to supply fuel, and you need to crank the engine over to pump fuel into the float chamber before you can get fuel into the engine.

Certainly my car with electric fuel pump and sidedraught pumped accelerator jets means it always fires as soon as I blip the throttle (although I choose to crank it for 5 sec first, to get the oil pressure going before it fires).

Loss of compression through oil draining back might be another reason for hard starting on engines with worn rings.

 

[AliK]

Great discussion and input fellas - thank you!

She's fine starting if left for a few hours but over night esp if cold I really have to wrestle for a good two minutes and the battery starts to show the strain just before it goes. I just did a video after two days of standing post Japfest and this is a normal start, sadly she didn't do her usual playing up. I will have to do this again at the weekend. Japfest morning she was parked outside and did the very difficult start up.

https://vimeo.com/164315331

I am on the mech pump still.

Spark plugs I use ....

 

[STEVE BURNS]

Well I think you need one of these!!

 

[ddhchp]

Starting

HI
From the vid sounds like fuel starvation. Try removing the fuel pump and actuate it manually loads from cold one morning until you feel the petrol is pumped up to fill carbs.Re fit and try a start then if that works. replace the diaphragm or the whole thing.

Dean Halsey.

 

[Rob Gaskin]

HI
From the vid sounds like fuel starvation. Try removing the fuel pump and actuate it manually loads from cold one morning until you feel the petrol is pumped up to fill carbs.Re fit and try a start then if that works. replace the diaphragm or the whole thing.

Dean Halsey.

Yeh, I've had a faulty pump - one of the valves wasn't 'shutting off' completely. Once started it would run but it took a lot of starting - I even used Easy Start.