EEC IV V-Pwr vs battery voltage

[OX1]

How close should it be? I get a .2 volt drop between battery and V-pwr on break out box. Using RJM harness, about 5 years old and 5K miles, tops.

Having a warm engine start issue, after about 30 minutes (cold and immediate start when hot, OK), seems like spark (get spark on plug tester, but it appears a bit weak).

Investigated NSS wiring vs EEC issue, that is not it (also looked at EEC board, and that trace is not burnt). If I put on battery charger/starter, which cranks voltage up to 15ish, it will then start warm.

Swapped out EEC to known good, 2 TFI's (even tried DUI Dyna Mod new TFI), new MC coil, known good distr, new MC distrb cap. It already had new battery and new high torque starter (both one month old). Only thing left original on wiring is starter wire (that runs from starter to where start solenoid used to be)

It is not a fuel issue (two fuel pressure gauges), Binary Editor shows injectors PW during crank. No codes except 15, which I'm told is normal with Quarterhorse. I can create accurate code by removing ECT or TPS connector.

Going to wring out grounds today, but they all show good on the breakout box so far.

 

[EFI Guy]

I wouldn't worry about voltage drop unless you are in the .5 volt range or higher.

How sure are you that the spark is weak?

It sounds more like a fuel delivery issue if it only happens at a given temp. The first thing I'd check is the fuel pressure regulator. Pull the vacuum line off of it after it has been running a few minutes and look for signs of fuel leaking past the diaphragm and in to the vacuum line.

After that I'd look in to your tune. Especially if your are getting code 15, BE has the ability to calculate the checksum so you really shouldn't be tossing that code.

Voltage plays a huge role in how injectors react. Are your injectors stock? If not did you change the Offset VS battery voltage table?

How about cranking PW vs ECT? That one gets a lot of people because those settings aren't part of standard published injector data so it often gets overlooked even though it's critical. You can add or subtract a few % in the temp range you are having problems to see if it helps.

 

[OX1]

I wouldn't worry about voltage drop unless you are in the .5 volt range or higher.

How sure are you that the spark is weak?

It sounds more like a fuel delivery issue if it only happens at a given temp. The first thing I'd check is the fuel pressure regulator. Pull the vacuum line off of it after it has been running a few minutes and look for signs of fuel leaking past the diaphragm and in to the vacuum line.

After that I'd look in to your tune. Especially if your are getting code 15, BE has the ability to calculate the checksum so you really shouldn't be tossing that code.

Voltage plays a huge role in how injectors react. Are your injectors stock? If not did you change the Offset VS battery voltage table?

How about cranking PW vs ECT? That one gets a lot of people because those settings aren't part of standard published injector data so it often gets overlooked even though it's critical. You can add or subtract a few % in the temp range you are having problems to see if it helps.

One for the archives I guess. As mentioned, I am using an RJM harness. I ended up lengthening the main power (direct battery) wire that that harness uses, which supplies feed to 4 relays, Ign, EEC, FP, and MAF/O2's.

Those 4 relays are each fused, but that long run straight to battery is not. I added a 30 amp inline fuse holder right after the battery to protect that wire.

Anyway, either my extension was bad, which was 12 guage soldered to the 14 guage that was supplied, or that inline fuse holder is bad. Just temporarily, I ran another 12 guage wire straight from bat and just touching where that 14 guage feeds the 4 fuses for each relay. My drop with engine off, ign on went from .2 to .08 volts.

Cut that 14 ga right at that 4 gang fuse block and crimped (not even soldered yet) on a 10 guage straight to bat. Problem solved, starts when warm, tried 30 and 45 minutes after hot shut down. Also starts much quicker that it did before cold.

The spark looked weak on a spark plug tester, just from 30 odd years experience of messing with motors. This is what I suspect was happening. Motor is new and almost 10:1. When motor was cold, it spins free-er and draws less, giving EEC/Ig just enough to get started. Even then it was what I would consider a "long" start compared to what I know a good starting 5.0 EFI would typically take (my first new car was an 86, 5.0 Capri, which I still have).

When motor was hot, it was more bound up, but 3G was charging batt up wards of 13.5 volts, so the EEC/Ig still got just enough to start.

Warm start still had a tighter warm motor, but the extra juice from batt had settled down to batt voltage at that point, so no start. I suspect that volt drop was even greater to EEC/Ign under start cond, but no way to really measure since even ign coil goes to zero on voltmeter during start.

So anyway, one more thing to check for anyone having a long start or warm start problem.

As for the other items. I had read that in the settings of Binary Editor, you could elect to have it recalc checksum each time you write, but I could not find that in the settings tab. I did also read that it won't hurt anything either way with that code.

Appreciate the other suggestions. Will revisit those, especially PW vs ECT. Might be something there too, to refine it further. Cold start, it fires instantaneous, but hot and warm start is still a bit slow compared to what I'm used to.

 

[EFI Guy]

Glad you got it figured out!

You are correct, an incorrect checksum won't hurt anything. I recommend setting it right because tuning devices can be buggy and easily corrupt a tune. It happens more than most would think. If your checksum is calculated correctly and you later toss that code it's a good indication that something may be wrong.

I don't use the auto calc feature either. But once I'm done tuning for the day under settings / User_Pref, there is a big grey button in the top right of the window that says calculate now. Hit that, then save and write the tune.

 

[OX1]

I'll look harder............;D

I personally think a single 14 guage was kind of light for powering all 4 of those relays (on an otherwise really well done harness overall)

Especially since FP relay is on there (mine just powers an additional relay that has 10 guage running straight to pump).