Hey- looking for any similar experiences re: ECU to injectors pulse control:

2002 Blazer 4.3L w 167,000.

Bought off owner who reported "ran great and suddenly would only idle. Some brain trust told him his timing chain broke so he panicked and put it up for $500.00. I replaced the distributor and some minor stuff and presto!

Started right up and idles very smooth and consistent...at 580 RPM, but cannot throttle up- immediately fuel starved. Can monkey around and feather the throttle until 1000-1200 but not for long; rough / leaned out, take foot off of pedal and drops right back to a smooth steady idle... 580 RPM... for hours, if I leave it. Runs at 185 degrees, no other problems except I can't go to the movies. Starts immediately even at 20 degrees.

Fuel = 62 psi KOEO and 58psi running. Can hold about 55 for 4 or 5 hours and holds 48psi all night. (No problem with fuel pump.) I can back probe 13.8 volts (+) with a (-) ground present at each of the six paired injector leads, but I have no way to strobe the grounds for pulse width... so,
wondering-

Are the GMC ECU's capable of having such a "discrete" and specific failure? I pulled the cover off of the computer; very clean pins & edge connector... no burned traces or blown Pico-fuses on the card and the power transistors tested intact with a diode check.

Throttle Pos. sensor reads nice smooth transition from 0.10 V thru 4.88V with no flat spots or blanks... seems fine.

Mass air flow, hmm don't know. I can idle equally well, with it unplugged or plugged in... or without the air tube even attached. Possibly though- a quality value is required from the MAF for the ECU circuit to modulate the injectors bandwidth ???

I cannot believe all six injectors or poppets suddenly plugged off, and that's how the former owner reported this happening. No gradual failure... just all of a sudden Kaput! They idled on in to a "mechanic" who told them their timing chain broke... they panicked and threw it out onto Craig's L.

I am off to purchase a cheapie code reader... got plenty of books and I suppose I could check grounds again, but all the grounds at the ECU show good conductivity at the harness. Only visually inspected the harness- clean and didn't go that way because I can read +/- 13 volts on the injector pairs.

Maybe the injector block fried all at once due to surge, momentary or sumtin ?? Is there any reason to flash the ECU or is that a myth that they can lose their program.. or can they even function partially?

Thanks for any similar SNAFU's and clues. I'll get after the codes.
)

 

With the symptoms you describe, I agree, it sounds like a lack of fuel pressure, or volume, or both. 55psi leakdown for the entire system is borderline, but within spec. The KOEO pressure of 62psi at the service port, could be, (not necessarily) the regulated fuel pressure, or fuel pump maximum output pressure, whichever is lower. If regulated pressure truly is 62psi, the regulator is fine, but if the pump can only build 62psi, and the regulator is adjusted for 64psi, that's a huge problem. You have no way of knowing if the pump is good or bad, without checking it. This link explains: https://blazerforum.com/forum/2nd-ge...eakdown-88305/


Make sure the fuel filter is not restricted, and post all 4 readings from the link. We can help you analyze the results. Also post the DTC's that are in memory, in the order they are retrieved.


The injectors are not paired, they a fired individually, and sequentially, when the PCM applies ground to them.

 

Hello Captainhook!

Hey, thanks very much and sorry 'bout late reply. Been stupid busy and lots of snow in Como. Plus it was St. Patrick's Day and with the typical luck of the Irish, she still dogged down. But I have a little dough saved up now and time so:

The little I did was to pull off the plenum and inspect and measure:

1. Fuel pump line inflow deadheaded = 107psi & 78psi about 12 hrs later.
2. Regulated pressure = 62-63 psi and held 58-60 overnight.
3. The little injector screens on every unit seemed gummed up and a
couple of poppets were blackened w/ four of them clean. All of them
actuated with a 9-volt battery...clikkety clik. I threw that entire
assembly in the back of the garage. 187,000 on that w/ no leaks!
4. Purchased a new (original style) assembly, gasket & fuel line O-ring
kits- meticulously cleaned surfaces and reassembled... corrected a few
minor vacuum leaks on the way and purchased an OBD II scan tool
w/ blue tooth to phone link (Bosch Model 1050). Started right up
and stuck on idle. Opened beer.
5. Codes read out with Open Fuel Circuit 1 and then Open Fuel Circuit 2
and then the P0118- well, yeah, temp sender plug end is a mess...
and will replace that tomorrow- but I can "make" it for a few minutes
before it falls off again... no difference in idle, however. (Incidentally,
the unplugged high voltage state correlates to -38 degree F in GM's
literature... so that probably should be causing a rich cold start mix.)
Gotta fix it, regardless... then it listed a P0171 (adaptive lean) and
then listed 3 I/M monitors completed and passed for misfire monitor,
fuel sys. monitor and comprehensive components monitor. Those 3
checked off ok.
6. With the engine idling I will judiciously but cautiously *smack* the
PCM and wiggle wiring harnesses there and at the injector plug end.
No differences noted but (!) suddenly did produce a bit of increase in
rpm when I twisted the plug end at the TPS !

So, more tomorrow. All this 'verbage' is just to share the final
outcome. I have the pin outs and procedure to check continuities
(safely) at the PCM harnesses to injectors.
Even though I do read a smooth 0 - 4.8V
across the range of the throttle position sensor, I'll change it anyway
because it acted flaky. But, hmmm- it's not throwing a code or I'd
suspect the back probed volt reading at the device may not be what's
coming in the gate at the PCM. (Volvo harness experiences- bad ones
in the 80's!) and some Chrysler and Ford 1st generation injection.

Plan is check all harnesses... probably splice in a new injector plug wire harness / connector end, or try to "Bob-job" a refurbish... nawww. New one! New one is only $27.00... then if no progress, have towed for a flash or bench check the program. I hate throwing in the towel like that because a replacement PCM is $116.00 and the dealers near me want $100.00 to possibly tell me the computer is A-OK. Maybe get one out of a running wreck, known to work and try a swap to see if I can move the problem around...

I have a 92 Blazer 4WD, this 2002 Blazer 4WD and a 1970 C-50 dump truck with a 283 and 4 speed x 2spd rear end... harvest truck; like a school bus. Solid. I am almost stupid enough to hot rod the 283 into the blazer but just smart enough to know how dumb I am. So I won't. I'll fix this Blazer!

More later. Thank you!

P.S. One site with pin outs for the Chevy 4.3L, 5.0L & 5.7L PCM connectors is found at troubleshootmyvehicle.com and most Chev dealers Parts desk will print one out, too.

 

PPS- I meant that the fuel pressure (deadheaded) slowwwwly drops from 107-110 psi to 78 pounds over a 12 hour period. It pops to 107-110 with key on. New fuel filter and ample flow volume. No longer suspect the fuel train.

(Funny- no P0200 code thrown (injector circuit control), but not that funny. Cryin' shame!)

 

Ignition problem misfiring under any load or timing except at idle?

 

Turning attention towards my PassLock system: Had armed (shuts off the injectors in my 2002 version) and required either a scan tool or a disable and or reprogram the PCM to eliminate the disable. I never heard of PassLock or VAT's or Passkey II or PK III, and apparently I am not the Lone Ranger. The amount of misinformation and mixed up terminology out there is just enough to make you dig a little deeper. My system (PassLock) is a set of hall effect switches integrated into the lock cylinder. There is no transponder (freq RC) key or bullet resistor key involved (other Chev's, different years). Remove steering cowling... 18-20 ga wires (3) orange/black... white/red (12V+) and yellow. Monkey around with the plug end. Pinch the release. Inspect the connection for corrosion or smarm... and learn about the "Relearn Procedure" (cycling key... 3 X 10 minutes... flashing security lamp, etc.) especially if you've had the battery out for 3 years, or you were in prison while your 9th Grade kid brother had the car out with his midnight auto club buddies... or, if like me, you bought a super sweet "deal" on C.'s List... partially disassembled by the partially knowledgeable.
Like me- never heard of 'PassKey' or VAT's...or PassLock, yet I would sit over this going on with, "Hmmm... great fuel pressure, great spark, idles great, new injector pack (insects have 6, spiders have 8 by the way) TPS is fine, Mass Air is fine, Temp is A-OK, PCM is new... and programmed to run, the "Key-Re-learn" went smoothly... IAC is great... vacuum is optimal... how can this be?" No codes thrown... (course, without a proper scanner I can't see dynamics)... although "Open Fuel Circuit" did show up on my Chev OBD code...after it idled for a while. No security light on dash... hmmm.

My PassLock system turns off the injector drivers in the PCM, period. I only assume my BCM is OK 'cuz all windows, instrument gauges, interior stuff and cig lighter, radio, overheads and rear facing rocket launchers still work fine. However, the required decoding and switching to the PCM injector drivers (power transistrs. to pulse grounds sequentially to the injectors) all originates in the BCM. So it probably will be BCM edge connector or something. Off to the power geeks at Car-Toys. They'll already know exactly how screwed up this is! Downward bound GM!

 

Update w/ Potentially Useless Info: Here is an excellent primer on three possible (GMC anti-theft systems:

http://my.cardone.com/techdocs/PT%2077-0011.pdf

This tutorial will introduce you to the differences between a "chipped" key system, a resistor in the key system and a coded lock barrel (hall effect switches w/ resistors) system. VAT's, Passkey, Passkey II are all different circuit completion mechanisms... but all these variations only switch on the weakest link in our oldie but goodies, and that's the Body Control Computer. The BCM must then successfully recognize the code from the lock cylinder, or the transponder key, or the resistor key... and then it must close a switch to feed the PCM injector control ground pulses (on my '02 Blazer). So I was lucky to by-pass the key lock mechanism but I doubt it really was the problem. I'm still waiting for my BCM to take a dump. Today I'm researching whether the PCM can truly be "reprogrammed" to disable any need for PassKey or VAT's... however,
Re that: Check out Newrockies, Inc. (Canadian- Newrockies.com) (expert & informative!) where, for a mere and approximate $325, they boast and feature a conversion which completely removes the BCM and the ignition key interlock by circumventing the correct switch directly to the engine control computer (PCM); by-passing the BCM completely, allowing your stricken Chev to start when you turn the key... just like the good ole' days.

 

Sorry Les- Negative. New distributor and plugs and wires. Very smooth and even. Simply no fuel feed from Injectors... no codes... all components produce good millivoltages or resistivities... just learned about the stinkin, no good, yellow bellied, dirt eatin' etc etc anti theft interlocks. Now I know I'm old. I haven't been keeping up.
Pretty sure it will be my BCM or the simpler upstream key interlock. My 2002 4WD Blazer VIN was decoded by a dealer here: I have the PassLock (no "special" key) just a coded tumbler... that can be bypassed, but won't help if it's the BCM. Body control computer simply continues a circuit if the key code closes a circuit... then more chip-chip to close a switch to enable the PCM injector drivers. Yikes. It quit snowing yesterday (May 1st) so I can continue to calmly tear my hair out while smiling.

 

The PCM and BCM in these vehicles are darn near bulletproof and rarely, if ever, fail. If they are replaced, it's usually due to a misdiagnosis. Installing resistors, etc, to "fool" Passlock, is just begging for more trouble. Any GM dealer CAN reprogram it for you, the problem is finding one that WILL It's not a big deal, and certainly nowhere near $325.