whalepirot

Pulled the PITA Lingenfelter intake to check for pinched wires to the FIs. Maybe relieved it, but I started checking resistance to ground in a number of places, with my digital VOM. I NEED to ensure of a fix before reassembling it. (FelPro should make Velcro gaskets for this unit.)

I'd just driven the car after having this intake off/apart for another issue, parked it -- No start after about an hour; code showing the short, as above.

Comparing the L/R side ohmages, ( no tech detail of that sort is available to me) the L side was near zero.Pulled only #1 & 3 inj plugs (only ones accessible, w/o further disassembly); both checked around 15 ohms, as did #7 & 8. Those plug lead's resistances matched also, UNTIL I checked with #3 plugged to its injector, whereupon it dropped from the 5.4 ohms, to 4. That would tell me the injector is shorted, IF it hadn't checked at 15 ohms! With four (each side) injectors connected in parallel, as they are, the theoretical resistance would be 3.75, reasonably close to the observed, given the unknowns in the remainder of each (L/R) circuit.

I must be missing something here; comparable readings everywhere and the 'problem' injector testing okay as does its plug,...

Are there resistance specs or procedures that differ from what I have tried? thanks for any support.

VetteVet86

Need more specifics from you. I'm confused as to whether you are measuring injectors(only), harness(only) or taking readings with some or all of the injectors hooked to the harness. Also, do you have the other end of the harness(ECM) disconnected? I can understand measuring the harness resistance to ground with injectors connected, but you need to have the positive(battery feed) and negative(ECM) sides of the injector harnesses disconnected. Pull the injector(s) fuses and unplug the ECM connectors, then if you have ANY continuity to ground on ANY of the injector harness wires, you have a problem.

Let us know what you find.

Jep

whalepirot

Thanks for the reply. I felt I was doing a poor job of explaining.

The fuses are out, disconnecting the power, but the ECM is connected. I was hoping to find the short an easier way.

I took comparative measurements with all injectors plugged in, one off, and two off. The odd thing is how all comparisons matched, until the #3 injector was plugged in; again, that injector's resistance was about 15.

I did not check any resistance at or of #2,4,5 or 7, as I'd found an anomaly at #3 and b/c they'd require pulling the runners for access, due to the design of this manifold.

As expected, disconnecting one injector on the 'good' side, increased the measurement, to a value identical to the 'bad' side. That seems to indicate that the problem is not with the ECM, the wiring to it, or with the other injectors and their connections.

I'll crawl under the dash (ouch, at my age) and disconnect the ECM, then recheck. With the injectors wired in parallel, though, isolating the short may be a visual task. I guess it's possible that the ECM connection may alter the comparison readings, but I bumped the starter as a check, with no change in the readings.

leesvet

The inj can short and still show a good value in the coil as far as the ohms are concerned. Ohms is just the resistance value for the coil. If there is a short that allows grounding when the coil is energized that may not show up by testing ohms until plugged in and turned on..running.
I've seen shorts that sent an arc from the inj body to the closest part of the intake. I've had it happen to my car.
The wire harness being what it is, under sized wire, and mfg'd with less than the required insulation, you could also have a cross-connection in the wires to the injectors. I had to chop out the entire left side of mine and solder in new wire, new inj plugs and all the other items on that side. The wire insulation was so broken that when laying on the intake it would short the whole inj system. When lifted up off the intake it was fine. No obvious exposed wire but LOTS of breaks in the plastic wire insulation...
Right side was inspected and there were NO breaks, no damage, no issues of any kind. Why, I cannot say.

Theres a couple possibilities to look at...hope that helps. EFI shorting/grounding issues can be frustrating..

whalepirot

Gosh, that's nasty. thank was a nasty deal you had.s Thee wires appear is great shape, the harness not having seen as many years as the car, with the redo. I moved another right-side wire that seemed tight under the rail (it's dang tight under that plenum), then rechecked for shorts. With that okay, I powered up and checked the fuses. Both held okay for some time and the voltages were identical, but I was not pleased with the fuel pressure drop-off.

Weird, I stumbled onto a post about that topic. Recalling the hot start difficulties, at times, I think I will send these FMC injectors for a checkup, despite their limited mileage. The incremental time/effort/cost..... A leaky injector would explain the start problem.

leesvet

recently saw the article about the mystery filter/can on the fuel RETURN line right next to the fuel filter pressure line....

turns out this device is a regulator/accumulator .... that is supposed to help maintain pressure and regulate back flow to the tank. Makes me wonder if it fails,. what happens???? hard slow starts due to no fuel in the rails? low pressure until the pump can make it up?
Not sure...but there has to be a connection to the many unexplained hard starts that come from nowhere. This thing has never been serviced, replaced as far as anyone knows. I am looking at it this spring when weather permits to see what exactly will happen if its replaced or removed. Better start ups? mebbe.

whalepirot

Interesting. I'd never heard of that device and will have to take a look.

The hard start on this 409 is due to one cylinder, seemingly havein a wanna-backfire or hydrolock issue. It fits with a leaking injector, but I should know in two days.

whalepirot

I'd like to know where this article is, in case the rail will not pressurize and hold.

RC, in Torrance seemingly did an awesome job on the cleaning and flow testing, plus new filters, in a day, as I needed. the rail is on, wires carefully routed, but I want to see the rail holding pressure, after I bribe the pump to run past 5 seconds.

ALDL, A-G, is not doing it.

Hooked on Vettes

On a 90 if you want the fuel pump to continually run.

With the ignition key OFF, you apply 12 volts to a 16 gage
Red wire that is bundled in the engine harness located near
the ECM under the hood. It's a individual wire with I believe
is a female spade lug connector on the end of it.

whalepirot

The ECM only is '90. The rest is '84, wire harness altered to run it; sensors as needed.

I have two choices to run the FP: 1) direct power to the pump feeder wire or, 2) grounding the relay lug with key on.

The 'mystery' fuel line component gives me pause, having never seen or heard of it.

Hooked on Vettes

The fuel line modification was for years 85 and 86.

http://forums.corvetteforum.com/c4-t...-bulletin.html

http://www.quayle-co.com/tsbs/86-234.htm

whalepirot

Aha. thanks for that. I suppose I could retrofit, but for two reasons: 1) bigger projects in the works, 2) hearing a couple fuel lines rattle won't happen, with this engine and exhaust.

Gracia!

leesvet

This device is also present on my 87...I actually missed it for 15 yrs. Last time I changed the filter I saw it inline up and over the pressure line with the filter...and wondered..wazzat?

whalepirot

I read that it may be from '85 to '89.