H4Inf

This is about my third attempt to describe this properly and try and find a solution.

I'll just describe what happens. It's night time so I startup the car, warm it up as usual, pop the headlights on and begine driving... no worries, I drive for 5-10 minutes. This is when the weirdness begins.

I'll be stopped at a traffic light and go to take off, push on the accelerator and it takes a few seconds for the revs to come up. I pull over, sitting in neutral, hold revs at about 1500. Every 4 seconds they drop (theres a bit of a backfire) and then rise up again. If the revs are over ~2000 this doesn't happen, the revs will stay constant.

Now to explain my setup.

13B 6 port EFI (with no aux port actuators - so wide open)

Fuel System:
Tank -> Filter -> Prepump -> Surge Tank -> EFI Pump -> Filter -> Fuel Rails

Ignition:
Microtech Digi Series 1 Pro, dynotuned recently. Only the secondary injectors are running (on the upper intake manifold).

Intake:
Custom cold air intake by myself. I built a box and cut a hole thru the right radiator bracket where the box connects to the area in front of the radiator.

More about the problem: So this problem only occurs when I have had the headlights on for a while. I also noticed that if I turn the headlights off, the problem still occurs for a little while ( I have not confirmed for how much longer this problem continues occurring... ). So this sort of tells me it is not directly electrical but perhaps a lag in the fuel system?

My next two steps are to 1) get a fuel pressure gauge and 2) install an oxygen sensor to hook up to an air/fuel ratio meter, so when this problem occurs I can check both of these.

And remember, my car drives fine during the day when I don't have the headlights on...

Any thoughts or ideas on my situation would be brilliant,

Cheers!!

Paul.

IanS

iTrader: (4)

Have you had the alternator checked? Maybe the alternator is just barely good enough to keep up with the draw on it during day and kinda craps out during the night time. Bad alt would make the battery weak also. This could cause weak voltage and then would cause pump to not turn as fast thereby lowering fuel pressure (flow) and making the car act funny. If not alt, could be wiring from alt to battery. I am really not sure but it is something that is normally free at most parts stores no matter where you are. I would think best bet is to have them test it on the car AND off as it may be good but wiring isnt. At least then you would know the charging system is good. Also check the battery while you are there. That is my guess. This way you would know for sure that the electrical side is good. Also may want to check the voltage at the pump if possible.

Edit: Also if voltage drop is present, it may not directly effect your fuel pump first. May affect the ignition first.

H4Inf

Something I hadn't thought of was the alternator, pretty much because I picked it up from a junk yard not long ago. I've been thinking of that as "new" and something ive already replaced... I'd better have it checked out.

I just recently ran a 70amp cable from the alternator to the battery + terminal, so there isn't going to be loss there... should I have a fuse between the alternator and the battery?

As you put it there, that would explain it. Today i redid all the fuel pump and relay connectors to make sure they were making good contact - which made no difference...

The battery is good and it always cranks over very fast and starts up right away. I'll run some wires from the pump and monitor voltage tomorrow night and see how it goes, I reckon you are probably dead on with the alternator being the problem here...

The stock voltage gauge is always reading aroudn 13 though... so I'm not sure? Even if I turn everything electrical on, the volts never drop below 12....

I have never really dealt with the ignition system, I don't know how it works exactly, where would the main current be running? I could try checking those connections and take some volt readings there...

When I turn my headlights on, I hear the alternator taking load, and the lights seem to stay bright fine... Do alternators have intermittent issues? I got this one (used) for like USD$100:
http://rx7.pw.cx/photos/AREAS/electr...le%2070amp.jpg

any other thoughts?

IanS

iTrader: (4)

What size alt is it? Is it stock size? It may not be able to handle all the extra stuff you are throwing at it.

Size meaning current rating. BTW in the FSM, it states that the 50 amp stock 12A alt puts out only 12 amps at idle I think. It was something real low like that. The alt could be intermittently going bad. If the alt is weirding out (putting out less current/volts) the battery gauge will still read correctly as it is still at 12 volts.

Kentetsu

Another thing that comes to mind is a short in your headlight system. This could possibly drain the battery and charge system over time creating enough of a deficit to effect the ignition system. However, if the headlights always remain bright (even when the car is acting up) you can probably rule this out.

IanS most likely has you on the right track. Good luck with it....

GTRay

which ignition system are you using? the digi series microtech is fuel only isn't it?

why aren't you using the primary injectors? does that particular microtech not have the ability to control staged injectors?

if you are running the 2nd gen coil based ignition with a crank angle sensor you need to make sure that your wiring for the CAS is sheilded. headlights draw rather significant current and can induce magnetic feilds that will disrupt crank angle sensor signals if the respective wires are unsheilded and within a few inches of the headlight wiring.

Ray

H4Inf

I believe its a 60 amp alternator, I'll have it tested and see how that goes then.... I was also thinking about my headlight wiring, perhaps something was causing a lot of resistance... I'll get the alternator looked at though.

Cheers guys

H4Inf

Hi Ray,

The ignition I am not so familiar with how it works. Yes the Digi is fuel only. I have a dizzy which is hooked up to 2 coils... I think electric dizzy? I really know nothing about how my ign system works. I have a photo here of the dizzy, perhaps you can tell me about it ?



Hmm my spark plug leads are next to the lines that run from the dizzy to the coils....

H4Inf

I was driving tonight. With the headlights on and the stereo only, my voltmeter reads about 12.8. Not sure if that means anything. I also experience hindered acceleration... The car just doesnt want to go....

If I sit at idle for a few minutes then floor it, it goes fine, or if i hold revs steady and then floor it.... Maybe the surge tank is emptying?

Kentetsu

How old is your fuel filter?

H4Inf

Both never replaced.. but remember this problem only occurs at night when my headlights have been on for more than 10 minutes . . .

I do plan on dropping the tank tomorrow, and replacing filters and checking the pickup. I need to get a tank to store my fuel in when I drop it.

vizion47

check timing

H4Inf

ok, I have now replaced both fuel filters and all the fuel hoses have been replaced. My fuel system is in top condition. (I have a fuel pressure gauge on the way to further confirm this...).

I also had my alternator tested... the autoelec said it was charging fine, so that doesn't seem to be the problem.

A few months ago I installed a new 70-amp wire going from the alternator to the battery + terminal, and I left the original wire as well which goes into the fusible links. So yesterday I pulled off the fusible link for the original alt cable, and I drove around with the headlights on for about an hour (in 2 sessions) without a problem. I even had the interior fan going as well, not a problem! Now the original alt charging cable actually goes thru casing with the dizzy sensor wires (to the coils).. perhaps there was some short in here (I havent yet removed the casing to confirm)... or perhaps its something else......

timing was checked when i was dynotuned... so i dont think that could have gone bad could it?

any ideas?