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ok u need to test if that is loss in the wire or just std voltage drop from running a circuit.
u need to put the red positive tester lead on battery positive and black negative lead on the + close to the pump.
to do this make an aligator extension for the battery and make sure it contacts good.
the drop MUST be less than 1.5 volts.(ideally leas than 0.8 volts).
if not, consider this an issue.
I'm confused as to what you are suggesting. If i were to do that i wouldn't get a voltage as i would have my meter on two hot leads.
i checked to body ground from the hot wire at the pump and the loss is on the hot side.
if i were to run an extension from battery to both hot and ground on the pump, then re test, i could then see if my load voltage changes.
the fp and b + jumper test was really low but the voltage from the cor that is normally sent, while the truck was running was acceptable at 13.14 imo, that being said, my jumper connection could have been poor. Or the wiring in that bypass circuit could be faulty, or even shorted to ground or frayed etc.
I'll look in my fsm and see if it has a schematic of the fuel pump wiring.
For the record, i found a pressure reading for the fuel system with the return line pinched in the fsm. With the return line blocked it should have 52 psi.
i think since i have a gauge I can use then i will look into the wiring, and see if my pump will actually put out 52 psi as stated with the line pinched. If it does build the pressure then i would think it's safe to say the pump would be ok.
also, i found the schematic and I'll see what my voltage is at the b+ terminal tomorrow to make sure I'm getting good voltage from my main relay.
I'm confused as to what you are suggesting. If i were to do that i wouldn't get a voltage as i would have my meter on two hot leads.
this is EXACTLY what im telling u to do. To get all theoretical and sound like a teacher,
"voltage is a difference in potential". :p.
u do exactly as i said and exactly as uve doubted.
any resistance in the wire will cause the section before the resistance to have higher potential and read its own voltage compares to the later section. (potentials) .this can only be tested with the pump running, as the voltage drop only occurs when significant current is carried over the line.
see here.
im not pulling ur leg.
this is a starter motor, but same principle. https://goo.gl/images/iSMJXh
heres a fuel pump harness being tested. https://goo.gl/images/vRQBE2
u should test both positive to battery and the negative to chassis side as indicated in that diagram.
yay i taught someone something today.
Last edited by Thommo Thompson; 12-12-2017 at 03:53 AM.
You know, i taught myself mechanics, electrical, etc by reading forums. Started 13 years ago in the honda tech forum. I learned by reading, doing, etc.
i went from a target employee, to an oil change guy, to line mechanic, to appliance repair man and then entered industrial maintenance where i went from a green horn who knew nothing about 3 phase, vfds, etc. I took the 2nd shift lead position recently from a guy who had been there 14 years.
what I'm getting at is, i say I'm self taught but in reality it's people like you who introduced information that i can expand on. I had no idea that what i thought was "me on the same wire" was an actual field check for voltage drop. I read up on it and see what you are saying now. I'll do that (those) tests and report back.
You know, i taught myself mechanics, electrical, etc by reading forums. Started 13 years ago in the honda tech forum. I learned by reading, doing, etc.
i went from a target employee, to an oil change guy, to line mechanic, to appliance repair man and then entered industrial maintenance where i went from a green horn who knew nothing about 3 phase, vfds, etc. I took the 2nd shift lead position recently from a guy who had been there 14 years.
what I'm getting at is, i say I'm self taught but in reality it's people like you who introduced information that i can expand on. I had no idea that what i thought was "me on the same wire" was an actual field check for voltage drop. I read up on it and see what you are saying now. I'll do that (those) tests and report back.
I have been working on cars since I could hold a wrench have a background in EE and ME and seen a lot of really weak troubleshooting in car forums but you have really good trouble shooting skills. It shows.
So I am anxious to see this thing fixed!
Last edited by Melrose 4r; 12-12-2017 at 11:32 AM.
I might just point out that article is specific to AC motors, which indeed have the characteristic of drawing higher currents at lower voltages, as I pointed out a few days ago. DC motors such as your fuel pump are a different animal, and the behavior of one type cannot be extrapolated to the other. At best your fuel pump could draw a nearly constant current as voltage decreases, because it is working into a constant pressure load, but it's not likely current will increase with decreasing voltage.
my battery is a little weak from all the trouble shooting I've done.
battery 12.05 volts.
B+ terminal 11.75 (this is from efi fuse, main relay, to test connector) so there is some loss there as expected.
when jumping the fuel pump in the diag box. I get the following.
on the hot wire, i record .112 dc. On the ground side also .112 . So total loss is .22 volts dc.
checking the pump, ground on battery, hot on pump i get 10.08 volts
checking the pump , hot on battery, ground on pump 11.74
so if I'm understanding correctly. My loss through the wiring is .22vdc. So i should have an unloaded voltage of 11.53 through factory wiring (higher with the jumper cable to battery as loss is lessened)
if my pump is running with 10.08 volts, with minimal loss on each line, then I'm losing about 1.5 volts through the pump itself. This is engine off so the fpr is under more restriction than with the engine running at idle
now the question is, what is the normal loss on this pump?
my battery is a little weak from all the trouble shooting I've done.
battery 12.05 volts.
B+ terminal 11.75 (this is from efi fuse, main relay, to test connector) so there is some loss there as expected.
when jumping the fuel pump in the diag box. I get the following.
on the hot wire, i record .112 dc. On the ground side also .112 . So total loss is .22 volts dc.
checking the pump, ground on battery, hot on pump i get 10.08 volts
checking the pump , hot on battery, ground on pump 11.74
so if I'm understanding correctly. My loss through the wiring is .22vdc. So i should have an unloaded voltage of 11.53 through factory wiring (higher with the jumper cable to battery as loss is lessened)
if my pump is running with 10.08 volts, with minimal loss on each line, then I'm losing about 1.5 volts through the pump itself. This is engine off so the fpr is under more restriction than with the engine running at idle
now the question is, what is the normal loss on this pump?
"Total loss" its not cumulative, you have a voltage drop of only .112 between battery and diagnostics connection.
You have a ~two volt drop from battery to the pump. This is probably a little high, but I do not thing its to high. Motors of this size tend to have an RPM/Voltage spec of 1-200/1v. So it's a little less volume, compound that with dirty/clogged lines and filters and you might have an issue.
Run a new line to it (temporarily), if the symptoms go away then you can start cleaning connections and checking the wire joints ect. You might just need a new filter sock, might need to clean the hardlines. a flow test at the pump, vs at the filter, vs at the return will point that out.
I might just point out that article is specific to AC motors, which indeed have the characteristic of drawing higher currents at lower voltages, as I pointed out a few days ago. DC motors such as your fuel pump are a different animal, and the behavior of one type cannot be extrapolated to the other. At best your fuel pump could draw a nearly constant current as voltage decreases, because it is working into a constant pressure load, but it's not likely current will increase with decreasing voltage.
Your right, i did a quick search for DC motor problems and that waas returned and assumed that because it was returned it must have been about DC motors! i was too quick to see something which backed up my comments to actually read it in full.
However, im still certain that undervoltage causes overcurrent in a fuel pump, because adam sais so. and adam is an obsessed autistic electronics genius who works for the Australian government providing electronics and IT consulting for the Health industry.
Last edited by Thommo Thompson; 12-12-2017 at 06:50 PM.
your wiring is fine at idle then, perhaps try it again at higher rpm, where system current goes up, jsut to be sure. anything more than 1.5V while running, on any of the wires, hot or ground, is too much.
The drop of 2 volts by the pump is about right, which is why you cant measure voltage drop across the entire circuit.
Nonetheless, id be 90% confident with those tests to say with those figures your pumps electronic supply are fine.
One more test would be to use an actual amp clamp, where the tester measures current int eh wire without actually being in series with it.
But dont go to those extents unless u have access to one.
My clamp meter only does ac current. I have to have my fluke in line for that.
I've been busy and haven't had the chance to pull the pump yet to check the filter sock for crud. We had one of our legs drop in our 480v supply tonight. I've been chasing blown fuses, tripped breakers, etc all night. We had a glycol pump catch fire, and one of our machines has two drives that got killed. Of course we don't have those drives here and even if we did, can't program them.
id say we will lose two days at least on that machine and probably cost us 20 grand a day.
what a night.
oh and I'm still here, probably for the next 4 hours as well. Love those 16 hour days
Finally an update to this. I have changed the fuel pump and regulator now and had no change. Problem persists.
at this point I'm going to pull the upper plenum and change these injectors out for stock and change the fuel filter again. It's brand new, but when i changed my fuel pressure regulator i noticed a brown oily substance on my hand that could only have come from the fuel In the rail.
92ehatch, it's time for a summary and clear restatement of the problem because just rereading the thread, it's getting a bit hard to follow.
Has this engine ever run correctly or did you get it in this state?
Do I have all this right?
*Compression test and leakdown now read normal?
*TPS sensor- voltages confirmed or unit was changed?
*fuel pump - has been changed. pressure normal? What is the fuel pressure number?
*injectors- not stock, unconfirmed, possibly gummed up.?
*backfiring in the plenum, consistent? which cylinder?- pull plug wires individually to see if it goes away.
How do the plugs look? consistent or does one look sooty and different than the other three?
92ehatch, it's time for a summary and clear restatement of the problem because just rereading the thread, it's getting a bit hard to follow.
Has this engine ever run correctly or did you get it in this state?
i rebuilt it, i don't know if it did this before or not.
Do I have all this right?
*Compression test and leakdown now read normal? Yes, faulty tool was the culprit
*TPS sensor- voltages confirmed or unit was changed? -Both
*fuel pump - has been changed. pressure normal? What is the fuel pressure number? I don't have the number, if i pinch the return line the truck runs fine.
*injectors- not stock, unconfirmed, possibly gummed up.? Brand new Bosch 4 hole injectors.
*backfiring in the plenum, consistent? which cylinder?- pull plug wires individually to see if it goes away. Only happens on throttle, there are videos showing this in the thread.
How do the plugs look? consistent or does one look sooty and different than the other three? Plugs look great.
basically, the truck will start and idle fine. When i drive it it drives fine, except for when i shift gears and initially hit the throttle. If I'm idling and hit the throttle it stumbles hard, back fires as well. If i pinch off the fuel return line it runs absolutely perfect, no stumble miss or backfires.
i have tested the afm, two different units. New tps properly set with feeler gauges, all new sensors for coolant, csi,etc. No vacuum leaks. Timing is spot on, both mechanical and ignition. New fuel pump and regulator. Good voltage to pump. New fuel filter, good compressing and leak down tests.
I never bought a fuel pressure tester. At 30 years old i figured a new pump and fpr wouldn't be a bad investment. Although i can still purchase the gauge set if need be.
Interesting find with the manifold off. The upper intake gasket is soaked in fuel in between runners 2 and 3. Which doesn't seal anything. Tells me there is an external leak. I have smelled fuel from time to time driving it but have never found a leak.
there is also a bit of fuel puddled in runners 1and 2. 3 and 4 were slightly wet but not puddled.
i ran the fuel pump with the engine off for about 5 minutes and there were no leaks that i could find. I then immediately pulled injectors out and no fuel sprayed. It leaked out of the rail, but definitely didn't spray like i would think if it was holding pressure. I'm lost as to where this fuel is coming from.
Raw fuel in intake runners 1 and 2 Soaked with fuel in between runners 2 and 3.
They are "supposed" to be the same size injectors, meaning no extra fuel. That being said, who knows what they are at this point.
I only bought them because one of the 4 originals was not original, it's some weird looking thing. I may have to buy a set of originals if i can't figure it out though.
I replaced the crush washers last night, injector o rings, and cleaned out the fuel rail and double checked my wiring for my injectors. If it continues then i will proceed with further pressure testing and possibly changing out injectors.
12-11-2017, 09:50 PM
