Fuel prob. - need an expert! plz, ty

[silicon212]

Originally Posted by tirion

Couldn't find the CTS. Having a car guy come out tomorrow and do a diagnostic for $30.

I wouldn't recommend anyone ever waste money on the books in Autozone BTW.

I resemble that remark! I have a copy of the Haynes B-body Chevrolet 1969-1990 manual and it helps me with things such as carburetor specs, electrical diagrams and schematics etc.

The CTS should probably be on the thermostat housing at the front of the engine. As was stated earlier, it will have two wires on it - one black and one yellow. The thermostat housing might also have a thermal ported vacuum switch on it - this will have two or three vacuum lines on it.

A CTS failure will set a trouble code and light up the SES light. This should set the computer into "limp" mode, but it shouldn't cut off the fuel pump.

I'm still trending toward the ignition switch as a failure point as it would explain both an intermittent ability to crank as well as the pump shutting down after a while - power breaks down at the switch, no more pumped fuel!

[tirion]

Gah!

guy just came out and checked it over and then used a noid light and said the injectors aren't getting pulsed. To replaced the ECM (PCM) - computer.

Said to make sure to remove the old EEPROM and put it back into the new one and to avoid bending any prongs.

Man.. if this doesn't make her fire up and go...

[FOCH]

Hello all
I have a 93 4.3 s/10 Blazer and have the same trouble. I would have bet money it was the pump.I replaced the pump (nope not it) if I shoot gas in the thottle body it will start till the gas is gone then just crank.Changed the relay on the firewall (Nope not it either) ??? But have power at the relay. The plug at the pump/sender is good but no power out of relay ?? I was looking for a fuse under the dash thinking maybe it cut off the power.. so wind up for now is I ran a hot line from the fuse box to the pump so I could use the truck till I find out whats wrong. There is a test plug on the fire wall if checked with a light it comes on for the 3 second start up...I am wondering about the ignition how would I check it out???
Anyway like to know how tirion makes out with the (PCM) I might be next soon.........
THANKS AHEAD OF TIME VINNY FOCH

[Supergumby]

Originally Posted by tirion

Gah!

guy just came out and checked it over and then used a noid light and said the injectors aren't getting pulsed. To replaced the ECM (PCM) - computer.

Said to make sure to remove the old EEPROM and put it back into the new one and to avoid bending any prongs.

Man.. if this doesn't make her fire up and go...

Before you put a new computer in, do this.....

Remove the four wire connector from the distributor. Turn the ignition to 'Run'. Now take a test light connected to the positve terminal of the battery, and touch the terminal from the purple wire with the white stripe. Every time you touch this wire with the test light, the injectors should fire.

If they do, the ECM can drive the injectors. If they don't, it can't and is probably suspect.

[tirion]

I don't have a test light... is there another way to perform this test? I have a voltmeter..

[tirion]

Found a used one for $40 with a 6 month warranty. When I went to pick it up, they didn't have it in yet.. be tomorrow morning. Called around looking for another (ECM) - and the other places were asking me which of the 2 I needed.. said there were 2 that had letters AB... and something else in their part number. But I have it pulled right here and there are no such letters.

It reads:

Service Number 16136965 AYAL

and *86AYALKB21781024*

shrug

always something...

[Blue Bowtie]

The eight-digit part number is important (16136965). The four characters after the number are meaningless as long as you have your original MEMCAL/PROM. The four letters are the broadcast code for the PROM, and denote exactly what engine, trans, year, etc. the programming is for.

Good luck with it. I suspect you may still have some issues after the ECM swap, but you might be lucky.

[tirion]

Can't do anything till tomorrow afternoon...what else could it be??

[silicon212]

Originally Posted by tirion

Can't do anything till tomorrow afternoon...what else could it be??

Well, let me see here. I do believe that I posted, twice, to check your ignition. I'm going to ask for a clarification here - by "not cranking", do you mean not turning over (starter not rotating the crankshaft, as with no battery) or do you mean "not starting"? They're two different things.

Let's do a process of elimination. You say that your car starts and runs for a while if you prime it. If the injectors were not being pulsed by the ECM, the engine would run long enough to clean out the liquid gasoline from the intake (and it would run roughly at that), about 5 seconds tops before it shuts off due to lack of fuel. You say it runs for 30 minutes or so - therefore the injectors MUST be getting pulsed. PROBABLY NOT the ECM.

The problem you are experiencing is generally due to weak fuel pressure or an intermittent electrical flow through the fuel pump. This being the case, have you checked:

Fuel Pump Relay
Oil Pressure Switch
Voltage at Fuel Pump

??

If the fuel pump relay is toast, you will be running current through the oil pressure switch. If this is bad, you will have problems!

Using a volt-ohm meter, ohm out the following-

Fuel Pump Relay - across the contacts - when the coil is energized, you should have 0 ohms across the contacts. You must perform this test with the wires removed - use battery power as a source for the coil.
Across the two opposing tabs on the oil pressure switch (|_|), with the wires pulled and the engine running - should be 0 ohms.
Across the coil of the relay (again, wires pulled off) should be no greater than 5 ohms (ideally 0, but allowing for some to count for resistance due to the inductance of the coil).

Using the same volt-ohm meter, test for voltage on the following with the engine running-

Across the coils of the fuel pump relay, wires connected, should be ~12 volts (13.8 etc).
At the fuel pump, positive lead on the 'hot' wire to the pump and negative on any exposed metal attached in some way to the frame, should be ~12 volts.

If you have infinite resistance (or anything greater than 1 or 2 ohms) across either the contacts on the relay, or the oil pressure switch, or anything greater than 5 ohms across the coil of the relay, these items are failed. Replace as necessary.

If you have no voltage at the pump or the coil of the relay, with the engine running, check for a bad fuse in either the pump or relay circuits. If there is no power to the relay, check the fuse and also the output at the ECM. If the fuses are good, check for wiring faults. Check for the presence of voltage at the ignition switch with the key on. Look at your wiring diagrams for the correct terminals to test. If voltage at the relay coil is good, but fluctuates at the pump, replace the relay.

You have a voltage problem. If a sensor had failed, the ECM will default to table data to run the engine, set the appropriate trouble code, and light the SES light. It should continue to run, however.

[tirion]

Right. Does turn over, does not 'start.' Sorry, wish I knew more of the lingo - by no means mechanically inclined at all.

By 30 minutes or so - I mean ONLY if I hold my foot on the accelerator. As soon as I let it return to IDLE - it dies.

I looked at the noid light and it did not come on at all when connected to the injectors. The mechanic guy said it was the ECM. Shrug. That's all I know so far. I get one tomorrow for $40 bucks, and will try my best to follow those excellent instructions with my voltmeter

Thanks for hanging in there with a noobie!!! ))

[silicon212]

Originally Posted by tirion

Right. Does turn over, does not 'start.' Sorry, wish I knew more of the lingo - by no means mechanically inclined at all.

By 30 minutes or so - I mean ONLY if I hold my foot on the accelerator. As soon as I let it return to IDLE - it dies.

I looked at the noid light and it did not come on at all when connected to the injectors. The mechanic guy said it was the ECM. Shrug. That's all I know so far. I get one tomorrow for $40 bucks, and will try my best to follow those excellent instructions with my voltmeter

Thanks for hanging in there with a noobie!!! ))

It does sound like you have a pressure problem. Have you put a pressure gauge on it? As Blue Bowtie suggested, it should be +/- 2lbs of 11 PSI. In fact,

Originally Posted by Blue Bowtie

With the pump relay operating, you still need to verify that the relay is providing power to the pump, that the pump is actually running during cranking (whether the engine starts or not), and that the pump is producing at least 11 PSIG pressure (bare minimum of 9).

If there is adequate fuel pressure, the inlet screens of the Maxi injectors in the TBI pod could be plugging.

[tirion]

Didn't have a pressure gauge.. but it dispensed what looked to be the same amount of gas/pressure from the filter break and at the TBI with both the old and new (I replaced it with a new one) pump.

I do remember the "check engine light" coming on several times, intermittantly over the past couple months, before it died on me.. when I would turn the car off to check the codes.. none would show. And now, the noid test showing no pulsing.. does that sound a little like it could be the ECM.. even though, it is giving and clearing codes now.. shrug. Up late, no new news, just thought I'd reply. Will post results of ECM replacement tomorrow afternoon (today actually)..

[silicon212]

Originally Posted by tirion

Didn't have a pressure gauge.. but it dispensed what looked to be the same amount of gas/pressure from the filter break and at the TBI with both the old and new (I replaced it with a new one) pump.

I do remember the "check engine light" coming on several times, intermittantly over the past couple months, before it died on me.. when I would turn the car off to check the codes.. none would show. And now, the noid test showing no pulsing.. does that sound a little like it could be the ECM.. even though, it is giving and clearing codes now.. shrug. Up late, no new news, just thought I'd reply. Will post results of ECM replacement tomorrow afternoon (today actually)..

If you're going to do this, and do it right, you're going to need the proper tools. You NEED that gauge. I've said it before and I'll say it again - you cannot gauge pressure by looking at a stream from a Schrader valve. All that will tell you is that the pump is working to some degree - it won't tell you that the pump is working properly.

[corning_d3]

Not only do you need a guage, but it sounds like you need a scan tool capable of pulling manufacturer specific codes. Most only pull the P0*** codes, not the P1*** codes..

[CD Smalley]

Nothing this old with TBI has ODBII. All he needs is a paper clip to get the codes.