Help! Short circuit, left side fuel "90 Sped Density

[WhalePirot]

Short circuit, left side fuel '90 Speed Density

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.

 

[WhalePirot]

anyone home?

Okay, I smell like exhaust again!

Got the wife's project car running well, so I did more research and then some Corvette checking. The car runs, tho not real well. I think some of that is remapping the fuel tables with the redone injectors, and it has improved overall, but (as usual) the hot idle takes the longest and affects the drivability, most; quitting at stoplights, etc.

The electrical is frustrating, given the low ohmmage of the injectors and the parallel circuit, but I believe that's the issue. The spark is okay on all 8, hard as it is to pull wires. My trusty inductive timing light is failing, but is the easiest way to check for spark.

#3 is weak, evidenced by no RPM drop with the wire pulled and the plug looks brand new; surely not firing with no fuel smell. That injector has 12vdc with the key ON. #1 plug has some rich fouling, due, I surmise, to the injector renewal flowing more.

The miss, not easily discerned due to the aggressive cam profile, is most apparent under acceleration. If the inexpensive IR temp reader is accurate, the left side exhaust runs 100 or more degrees cooler. I listened for clicking on each injector with my stethoscope. The right side units clicked more loudly. I could hear plenty of noises on the left but little or no injector rat-a-tat as they open and close.

I just realized that if the left bank was shorted to ground, the injectors could be always ON, allowing fuel to always flow, which would explain the low left exhaust temps, explain the partial carbon traces on some plugs, allow some power from that side and thence, a weak indication of miss in the exhaust note, yet a definite loss of power overall. It would also explain the lack of fuel pressure holding after shutdown.

Back to the electrical: four 15 ohm loads in parallel is 3.75, barely above a short. I recall one reply about disconnecting the ECM and checking again. I resisted having to do that; a chore of discomfort.
More later.

 

[WhalePirot]

please......

Borrowed a noid kit from O'Reilly and #1 & #3 show no trigger; not a huge surprise, really. #5 and #7 cannot be accessed, but I doubt the indication would differ. #8 blinks, showing the test bulb as operational while verifying the right side's higher exhaust temperatures.

I got about 3.75 ohms on both sides, across two different injectors on each side, with the INJ fuses out and the ECM disconnected; exactly as four 15 ohm loads should be. The was no short to ground on either side, either.

Despite warning to the contrary, and suspecting perhaps a bad ECM control(transistor) on the left bank, I checked for a GND short on the output pins to each bank; no short., but also not necessarily indicative of anything.

This ECM matter is complicated by the car being an '84, the harness modified to run from a '90 Camaro ECM and my reference FSMs are all Corvette: 1984, 1987 and 1990. None of those pin diagrams matched up to this ECM, but I found diagrams on the 3rd Gen site that seem correct. I was told by the harness modifier and source for this ECM and many sensors employed, that they differ by the weatherpack design for the Vette (mounted in the '84's stock location).

It appears the problem is the ECM, tho i hate throwing parts at a problem. I can find no test to verify the ECM is good or bad.

Comments?

 

[WhalePirot]

Talking to mee-self here......... Just in case it helps someone:

Pulled the harness-side pin from the ECM, then checked that it was continuous (.04ohms, actually) to the left rail and not shorted to ground.

Reconnected the ECM with that pin still extricated, installed a NID light in #1 injector plug and turned IGN to ON. With a long jumper wire clipped to that pin, I grounded it by tapping the other end and observed the NOID light flashing. Then, with IGN-OFF, reconnected the plug to INJ #1, then used the long jumper, with IGN-ON to verify audibly, injector operation.
The wee clicks emitted by the left bank injectors had me tapping like a fool!

Advice from a reputable injector specialist, via another Vette forum, had been to do more troubleshooting before replacing the ECM. Once again, the seemingly more involved path of pulling the ECM and the pin, was much more direct than the easier, softer-seeming method of checking resistances under the hood. The other recommendation was to get an A1-Cardone remanufactured unit, versus the cheaper Mexico-sourced Standard. Checking NAPA for price and stock, did not reference Cardone, but the description was an obvious cut/paste of their process to improve reliability and ECM life.

Plugging in the 'new' ECM, I checked the system with the pin re-inserted, with a NOID light: No flash! Crap! Back to square two? But..... the car had fired and seemed to run better, so I plugged inthe injector back in and fired the car up.

The result was readily apparent. See, I used a Chinese tool to boost idle RPM, an old chopstick inserted into the idle stop lever! The idle was so high and steady (relatively, given this cam grind), despite the EMC not yet relearning the fuel trims, that I removed said high-tech Asian implement. the engine continued to run okay,if quite rich, but leaning and learning. the miss when blipping the throttle was gone and my heart was racing along with the engine. Could it be? After all this time, bleeding and effort?

I decided not to try to understand the lack of a NOID light, having a Check Engine light to look into, then re-address the reluctance of the thermal switch to fire off the cooling fan, despite its new site in the thermostat neck.

It never stops; custom car issues, but the day is much brighter, and way noisier, in my garage.

 

[WhalePirot]

The CE light was not an issue (Code 44- O2 sensor) and the car runs just as scary as ever, tho the hot start problem has recurred. Last evening, it died on me as I arrived to an audience of pals (of course), but the car started well after sitting and cooling off. I reasoned that the oxy sensor was carbon-fouled due to the rich running, which was remedied by some rather fun (spirited) driving.

I'll start with checking and cleaning all connections.

 

[G Winter]

If I understand right ,you are running a port injected system on an 84 with a 90 ECM.
I tried to follow your injector ohm testing and got the idea you didn't disconnect the
wires from them to check. This seems to be a possible feedback. I am thinking that
you have to disconnect the wires to check the ohms correctly.
The hot start issue makes me think injector leak down or bad fuel pressure regulator.
I assume you have done a pressure leak down test ? Hot start issue could easily
be an ignition component problem.

brain storming for you .

 

[WhalePirot]

If I understand right ,you are running a port injected system on an 84 with a 90 ECM.

Correct, 1990Camaro ECM (not in weather pack)

I tried to follow your injector ohm testing and got the idea you didn't disconnect the wires from them to check. This seems to be a possible feedback. I am thinking that you have to disconnect the wires to check the ohms correctly.

that's true and I finally crawled inside and removed the multi-pin connector and both INJ 1 & 2 fuses for the resistance readings. An obstacle was, the pin layout for the Corvette and Camaro ECMs are not identical and it was vital to find INJ1 pin to ensure I was checking the wire I intended to check! I made a small pin removal tool by hammer-flattening a piece of wire.

The hot start issue makes me think injector leak down or bad fuel pressure regulator. I assume you have done a pressure leak down test? Hot start issue could easily be an ignition component problem. brain storming for you .

Appreciated, and the injectors were cleaned and checked by a good place in Torrance, CA. I have print-outs of their flows and double checked their reputation with a reputable competitor in Georgia.

The pressure regulator was replaced but there is still a leakdown issue. Another member remarked that his does the same, but his car runs well, as does mine. Someone referred to a check valve, which came on later production cars than mine, '86ish. I neither see nor smell any leakage atop the manifold, at either the crosstubes or injectors, nor on the tube junctions at the rail. The oil seems to have no gasoline diluting it, which some said could quickly happen.

The ignition module is new, tho I don't believe the old one was bad. I bought three new ones, b/c of web reports that many new ones are garbage straight from the box.

I am about to check all ground and + connections and might add another grounding strap. I learned that computer cars cannot be too grounded. The charging system seems okay; has a new 130amp alternator, largely to ensure enough juice to run the big amplifier. I will also check again for gasoline odors on the dipstick.

Appreciate the 'storm(s).

 

[WhalePirot]

I was over-thinking this, I now believe, and have R/R'ed the SuperRam 3-4 time; lost track, but I am getting damn good at it!

I four the spliced 4-wire leads to the injectors tape wraps had deteriorated. they looked okay, but upon touch... well, I redid them, checked for shorts as before, then 'clicked' the left injectors manually with the ECM pin, also as before. I'll never know if the ECM was actually bad. The fuse had blown once and the ground side had indicated a short, so redoing both junctions will hopefully help the difficult hot start, IF fuel was dumping into the cylinder(s) anytime there was pressure.

Speaking thereof, new rail O-rings, in conjunction with the above, fixed the pressure leakdown.

I just finished reassembly and ran the car; sounds great, as it relearns the fuel tables. Then, this has happened before so, my zeal is contained.

I also fixed the interior footwell courtesy lights and reinstalled the panels; one for the first time in years. I made LED inserts as replacements for the stock lights. The result is not as bright a light (dammit), but low heat and power. An interesting find was the power failure to the right light was at the wire's connection to the plug, at the light. Some time ago, I LED'd the right map light, as the hot incandescent light was melting/deforming its housing.