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Old September 16th 2011, 00:17
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Steve C Steve C is offline
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Join Date: Sep 2002
Location: Sydney, Australia
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MSD issues with fuel pump relay, old mechanics proverb


I posted this on another forum, may help other users.

I've been doing a few things to my sons bug in preparation for drag meeting Warwick Queesland, something an old mechanic once told me came true "you will find all of your ignition problems in fuel system and all of your fuel problems in the ignition"

Its a 1904 cc motor, 90.5 x 74, twin 40 Dellortos, GB 309 cam (recently upgraded from a AP2), 1.4 rockers, stock valve V Force heads, A1 1 5/8 header, really old German 009 with Pertronix etc, A1 headers

I went to local parts shop to buy some new plugs, I usually use NGK B6HS, one grade colder than stock, they had some NOS Hitachi plugs, in stock in the same heat range, the boxes were very dirty but the plugs were in new condition, I thought what the heck Hitachi is a well known brand, oh and they had a projected nose so they were equivalent to a BP6HS, I've used projected nose plugs before with no issues.

I fitted these plugs and all seemed right with the motor until I had a problem that seemed to be blocked main jet, the car was idling but and appeared to run OK on the idle circuit then the motor would run on 2 or 3 cylinders where the car would be progressing to main jet circuit.

I cant tell you how many times I cleaned the main jets, I even fitted jet doctors to the idle circuit and double checked the float levels. After a while it would happen again, I was also getting what appeared to be fowled plugs but the plug colours looked fine.

On Sunday I drove about 100 ks on freeways doing the speed limit with no issues, Monday morning it was the same problems again, only this time the problem would rectify itself without the carbs being touched if I turned the motor off for a few minutes.

Forgot to say on Saturday I fitted MSD 6AL ignition, started the car at home sounded sweet, drove 200 metres and the car stopped, rerouted the ignition wiring back to stock, the motor farted a few times and ran OK.

I started thinking what is the one thing that I've done different, the Dellortos usually run like EFI, the motor is running sweet some of the time, the plugs, I bought a set of NGKs and all is right with world, I'm fitting MSD tomorrow.

So the proverb came true as it has in the past in my line of work.


next post I made

All was going well with the new plugs.

Decided to try MSD again only this time with a MSD blaster coil

Got just up the road and the car stopped again.

Fuel and ignition problem this time, I have an electric fuel pump in the car and a tachometric fuel pump relay to turn it on, the MSD doesn't send the correct signal to the tachometruic relay to make it operate.

This all happened 5 minutes before I had to leave for work, I will fit relay tomorrow that will be triggered buy oil pressure.


next post

I had a tachometric relay from a EFI BMW, but it didn't like the signal coming from the MSD, the tacho signal comes out of the MSD box and not directly from the coil -

So I've now fitted a double through relay.

87 not used
87A goes to the pump
85 goes to the oil pressure warning light wire
86 & 30 are joined and fed by the ignition switch

On this relay when its at rest with no ignition feed, no power comes out of the relay at 87 or 87A

Turn the ignition on and the relay gets earth from the oil pressure switch, no power comes out of 87A, it only come out of 87 which is not used.

When the oil pressure builds the warning light goes out and the relay has no earth so it goes back to rest state but power goes through the relay at pin 30 and on to 87A to power the pump, if there is no oil pressure the relay is earthed again which takes power away from 87A.

The BMW tachometric relay cost me about $80 or $90, the Hella double through relay was under $20

STI powered 1303 in the works.
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