TPI folks question for you...

[dyeager535]

Those that have swapped in stock TPI or an aftermarket setup that runs each bank of injectors on their own fuse. (two power wires/fuses for injectors, total)

Problem is that typically when the engine is started one time (sometimes not even one start) it won't restart. Not getting injector pulses when it won't start, but it is getting spark.

I "figured out" my problem: too much voltage loss when the engine is cranking.

All TPI stuff is run off the fuse panel accessory terminals, and each into it's individual fuse...as close to stock as possible. Already cleaned up/inspected all the ignition related wiring connections from the distributor to the ECM, no change. Had the battery tested, because the engine just won't crank much before the battery gives up, but of course they said it was good.

Checked voltage at the injector fuse when it was cranking, it was dipping down into the 8's intially (volts) then into the low 9's. Went ahead and ran a wire directly from the battery into the cab, fused two leads and connected those to the injector wires. Voila, starts when hot. Checked voltage to the injectors when it was cranking like this, and it was in the 9.5V range briefly, then went into the 10's. None of the other terminals on the fuse panel read any better when it's cranking. Went ahead and pulled the fusible link ends from the junction block on the firewall, cleaned them all up, but that didn't help either of course. (but they needed it)

When running or off, the difference in voltage from the battery to the injector feeds is almost nothing.

I'm curious how everyone else ran their injector power feeds, that may be different than my setup. I'm going to go look at the wiring diagram, and look into the ignition switch. Expecting that I am seeing this problem partially because the ignition switch isn't getting a real good contact, but I've gotta pull the steering column anyways. I know what I need to fix, now I've got to figure out how.

 

[ryan22re]

so where do these two fuses get power from? i think i read from the accessory terminals in the fuse block.

have you checked other 12 volt circuits (that remain powered) while cranking to see what kind of voltage these other circuits are getting? sounds to me like dipping down around 9-10 volts while cranking is pretty normal, depending on the age and condition of the battery. 9-10 volts at the injector should be enough to light a test lamp/noid light while cranking. are you sure that you are not loosing spark with your injector signal (like maybe an ignition module that craps out when hot?).

what about grounds? battery ground ok? what about from the engine to the frame? frame to the body?


ryan

 

[HarryH3]

The power feed route in GM's is tortuous. Try running a power feed directly from the battery to the main post on the firewall. That will bypass the battery cable and the wiring that comes up from the starter.

Also check the voltage at the battery while cranking. It's possible that the battery is just weak enough to cause problems downstream. A bad battery cable or even a bad starter can also cause a big voltage drop during high current draw.

High resistance in the ignition switch is a likely culprit on somthing that old. If you can get the meter hooked in, measure the voltage across the switch (black to the "input" of the switch and red to the "output"). If you see more than a few millivolts there while cranking, then you've found the source of the problem...

 

[Hossbaby50]

I have done what Harry has talked about. I have an 8 guage power wire running directly from my battery to the firewall post. I also have an Optima battery in my truck. I have never had that problem with my truck.

Harley

 

[Hossbaby50]

P.S. I rewired my truck with the 8 gauge wire because previously I had it run with a 10 gauge wire and a 30 amp fuse. I was on a heavy incline while four wheeling and I popped the fuse leaving me dead in the water. I am pretty sure it was the added strain of the fuel pump trying to pump fuel uphill along with the extra juice it takes to run the TPI. I was on the uphill for a few minutes and I had been floggin the motor a little to try and get up. I had also been running the truck all day too.

I rewired the truck with an 8 gauge wire and a 50 amp fuse and I have not had the problem since.

Harley

 

[dyeager535]

so where do these two fuses get power from? i think i read from the accessory terminals in the fuse block.

Correct...I used the existing accessory terminals on the fuse panel. Stock locking connectors, every connection I made soldered and covered with heat shrink tubing.

have you checked other 12 volt circuits (that remain powered) while cranking to see what kind of voltage these other circuits are getting? sounds to me like dipping down around 9-10 volts while cranking is pretty normal, depending on the age and condition of the battery. 9-10 volts at the injector should be enough to light a test lamp/noid light while cranking. are you sure that you are not loosing spark with your injector signal (like maybe an ignition module that craps out when hot?).

I tested all the accessory terminals. (all 8 rows across the top of the later fuse panels) Only a couple rows get power when cranking, but not with the key "off". All of those dropped down just like my injector feeds.

what about grounds? battery ground ok? what about from the engine to the frame? frame to the body?

Battery ground is good, engine to the frame was just replaced, and frame to body is intact and clean as well. Measured voltage when I ran the single 12V wire directly from the battery at the temporary splice in the cab, and used a spot in the cab to ground the meter, so I know groundings good.

Batt. voltage stays high enough when cranking because of the "bypass" routing working, (and measure voltage) although I know that it's not the best battery, even though it is just a year old. I can get maybe 10 seconds of cranking before it dies. Nonetheless, first startup of the day, as it's routed now, it typically starts fine.

My other concern is that maybe the injectors just aren't up to the task. I know I've got two that are in so-so shape as tested with the ohm function of the multimeter, I had planned to replace all of them anyway, and now that I can burn PROM's, I can order the SVO ones and set my chip up for them. No idea what the injectors need for voltage to run consistently. I'll try running a wire directly to the junction block from the battery and see what I end up with.

 

[diesel4me]

A thought...

I know little to nothing about EFI ,but from what your describing,it sounds like the same problem points had during cranking due to the ballast resistor or resistance wire to the coil hot lead..maybe you could use the "bypass" terminal on the solenoid to give full voltage to the injectors while cranking,just like they did with point many moons ago?....

 

[dyeager535]

Not a bad idea, but if I figure if I've gotta run more line anyways, and voltage drop is an issue, the least connections possible the better.

I didn't mention it before, but this problem was slow in coming on, it didn't just crop up over night, it's gotten gradually worse and worse.

 

[dyeager535]

Well, went out and played around with it.

Running the 8 gauge wire from the battery to the junction block doesn't work. Straight to injector feed, starts. Such a good idea too.

Pulled the column out, disassembled the ignition switch and de-pinned the ignition switch connector, and cleaned all the contacts. Reassembled, same problem as before. It was nice and clean inside anyways.

I'm not going to pull the fuse panel and do the same, and at this point that looks like where the "problem" is. I may go back and make sure that I get real good contact with the 8 gauge wire and the wires to the fuse panel, but I'm fairly confident it was ok as it was. Nevertheless, I may try that again, it's easy.

For anyone that was curious, (I was) here is what the ignition switch looks like on the inside. Not bad for 20 years old or so.

 

[dave_90_blazer]

when I put the LT1 in my truck, I didn't feel safe running everything off the acc. taps in the fusebox, so I used one of them the trigger a relay that is hooked to the 12v post on the firewall, that feeds both injector fuses, this gaurantees that you get full batt power on the injector fuses

 

[Hossbaby50]

My truck doesn't start off an ignition switch anymore. I have a direct line to the starter and my truck starts on a toggle switch. My ignition switch is also bypassed under the dash. So basically my truck is hot wired with toggle switches instead of an ignition switch.

Harley

 

[HarryH3]

I can get maybe 10 seconds of cranking before it dies.

Does this mean that t he battery can only crank the engine for 10 seconds before it dies? With a good battery you should be able to crank it for more like 10 minutes.

I was about to post the same "fix" that dave_90_blazer suggested. Direct power via a relay. If you really want to do it first classs, check out the "Cirkit Boss" aux fuse panels from Painless Wiring.

 

[dyeager535]

Good suggestions brought up.

Yes, like 10 seconds before the battery starts to slow down. Like I said, it was load tested by Schucks who sold it to me. And bench diagnostics are good because...? I really need to watch batt voltage as it cranks longer though, if my batt cables are overheating or the starter is screwing up, that will happen with increased run time of course. I think I can safely rule that out though, I never crank it for more than say 3-5 seconds when trying to get it to start without a pause, and if it will start, it's milliseconds.

A relay wouldn't add much complexity I guess, (even though I'm injected, it's still pretty simple IMO) I could easily trigger it off of the accessory ports, but then again all my additional fuses are in the cab, so I still end up with a long run of cable. I could easily rig up a test though, I've got all the stuff to do it. End up with about 5 of the same relays, at least I'd have a spare one with the dual fans being operated independent of each other... I'm liking this idea more and more, I just hate adding more wiring for something that shouldn't be an issue.

The accessory taps *shouldn't* be limited, they are all on 30 amp circuit breakers, run with solid copper strips, but maybe I should bypass those and see what happens, since I'm still fused beyond that point, and all the accessory terminals drop the same voltage at crank and are all through the same breakers. Another easy test.

 

[HarryH3]

Yes, like 10 seconds before the battery starts to slow down. Like I said, it was load tested by Schucks who sold it to me. And bench diagnostics are good because...? I really need to watch batt voltage as it cranks longer though, if my batt cables are overheating or the starter is screwing up, that will happen with increased run time of course. I think I can safely rule that out though, I never crank it for more than say 3-5 seconds when trying to get it to start without a pause, and if it will start, it's milliseconds.

Chase this problem first. If the battery is weak, or the starter is internally shorted and drawing too much current, then the voltage drop to the rest of the rig will exceed the specs. It could even be something as simple as a bad battery cable or connection. Don't overlook the ground side of the battery either. I've had starting problems in the past that turned out to be corrosion hidden underneath the rubber of a side post terminal.

Make sure that you have good cables. Some cheap "fat" cables use very little copper but lots of insulation. You want lots of copper. I've also seen corrosion hidden inside a cable where water had been able to leak in at the terminal and wick down the wire.

When you have a truck that will crank for minutes instead of seconds, then you can still add the relay for good measure.

 

[dyeager535]

Yeah, that was my intention to "fix" the battery issue, but unfortunately when I took it in to get it pro-rated, they load test it, and no return if it doesn't come back bad. I know it's bad, they just won't credit me (1 year old battery) if their machine tells them it's good regardless of my symptoms. Maybe I'll try to jump start someone and the terminals will get hooked up backwards... One of my tests was going to be with another battery, but I can't get my hands on a known good one. If my engine ground and positive batt. cable are good, there is no excuse for the battery to die that quickly...if it was starter related, that would have no bearing on the voltage problem I've having, since the fuse panel power feed connection on the starter terminal is external of the solenoid and getting batt. voltage. Even if it was somehow something external of the battery, a known good battery would prove me wrong or right solely based on how long the engine will crank.

I've had the terminals off the battery numerous times lately, and the contacts are all clean. Using stock GM ground cable which I "disassembled" the upper end of and cleaned the "hidden" portion, plus a newer aftermarket + cable that has exposed, easy to inspect ends. Since I know the battery ends are ok, from previous experience, if the bottleneck is in the starting system wiring (including the batt cable connections at the engine ground/starter) the battery cables should heat up noticeably, which isn't the case, and indicates to me that they aren't being taxed.

I could be mistaken on that, but I know when my cars starter solenoid was messed up, prolonged cranking turned the battery cable hot enough so as to not be touchable.

 

[dyeager535]

Well, just a bump with some additional info, hate leaving stuff unsettled. Not done yet, but closer.

Did some more research, and I'm getting closer. Since I dropped the column, running an 8 gauge wire from the battery directly to the ignition switch wire that powers the fuse panel doesn't fix the problem. So it's somewhere between the fuse panel 12V feed from the ignition switch to my injector leads. Already removed the shunts and circuit breakers in the panel, cleaned them up, used fuses instead just to make sure, and same problem.

The difference between start/no start is so close voltage wise it's amazing. This is why people hate electrical stuff though. Glad I still haven't put my dash back together.

Worst case, going to have to tear the fuse panel out and work on the hard wired stuff there to find the weak link.