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Cold start resolution?? - '90 K2500 5.7 TBI


webbch
08-13-2013, 10:43 AM
I was having problems with my '90 silverado recently where it would crank and start up just fine, but then die shortly thereafter. Subsequent attempts to start it would end with the same results. At some point, it would continue running.

It looked like there was fuel squirting into the TBI, but it appeared to slow down and stop as the engine died. So I wasn't ready to rule out fuel or ignition system problems yet, but figured I'd check the fuel pressure to ensure is was in the 9-12 psi range spec'd for these engines.

I installed a tee at the throttle body (see the fitting that come with this (http://www.amazon.com/Actron-CP7817-Throttle-Injection-Pressure/dp/B0006V2BK0/ref=sr_1_10?s=automotive&ie=UTF8&qid=1376407676&sr=1-10&keywords=gm+fuel+pressure+adapter) fuel pressure gauge) to measure the fuel pressure. While I was installing the adapter, I noticed a broken plastic vacuum tube that goes from the EGR vacuum solenoid to the front of the throttle body. So I repaired the vacuum tube.

When I turned the ignition key forward, I heard the fuel pump run, and fuel pressure looked good, but the engine was still somewhat warm. I let it sit overnight, expecting to see the problem the next morning when I first tried to start it. The next morning, with fuel gauge attached, I started the engine...and it kept running! So at this point, I THINK the broken vacuum tube may have been the problem. Tomorrow morning, I may try disconnecting it and starting the engine to verify the symptoms return to ensure it's not a red herring. If it is indeed the root cause, it's a $0.39 fix (short length of vacuum hose to splice the plastic vacuum tube back together) to a very annoying issue.

webbch
08-14-2013, 09:32 PM
The vacuum line was NOT the problem. I found a very loose connection on the ground wire between the engine and firewall. As a side note, my temperature, oil pressure and alternator gauges were displaying _slightly_ low before I tightened up the ground wire as well.

Since fixing the ground wire, I've had two successful startups without the engine dying. Keeping my fingers crossed. I think the bad ground was messing with either the ECT or MAP readings, causing the engine to shut down.

Quick question: While running, fuel pressure is about 12 psi. After I stop the engine, most of the fuel pressure bleeds off within about 15-20 seconds. Is that pretty typical?

2000CAYukon
08-15-2013, 02:03 PM
The vacuum line was NOT the problem. I found a very loose connection on the ground wire between the engine and firewall. As a side note, my temperature, oil pressure and alternator gauges were displaying _slightly_ low before I tightened up the ground wire as well.

Since fixing the ground wire, I've had two successful startups without the engine dying. Keeping my fingers crossed. I think the bad ground was messing with either the ECT or MAP readings, causing the engine to shut down.

Quick question: While running, fuel pressure is about 12 psi. After I stop the engine, most of the fuel pressure bleeds off within about 15-20 seconds. Is that pretty typical?

I owned a 90 K1500 5.7 for 20 years. My fuel pressure would bleed off quickly after shutting down so I think that was normal for TBI.

//2000CAYukon

webbch
08-16-2013, 05:44 PM
In the last couple of days, the engine died on me once while driving...while travelling at ~55 mph, not accelerating or decelerating, I didn't catch any odd behavior on the dash gauges. It restarted without a problem and no other hiccups. Idling at stops seems fine. Right now, whatever the issues is, it's too intermittent to identify.

I recently dropped the dash to replace the evaporator when I was fixing the A/C, so there's a lot of stuff that was "touched" in the process. Also, I've only recently started driving the truck a lot (it's been the "backup" and "load-hauler" vehicle for several years).

Schurkey
08-16-2013, 07:15 PM
When I had problems with intermittent stalling, the distributor mainshaft/reluctor was the problem.

Started out as a high-speed miss, got worse over the course of about nine months until I had random stalling. Eventually stalled and would not re-start. Had to be pulled to a shop. They replaced the distributor main shaft, but I suspect most folks would have shoved in a different distributor.

Mainshaft/reluctor goes bad, distributor ignition module gets no signal for spark, and ECM gets no signal to trigger the fuel injectors.

webbch
08-18-2013, 10:21 AM
Thanks! That's a real gem. Did it set a code when it died?

Since I always had good fuel pressure when the key was turned forward and during the times it was running, I think I can rule out the fuel delivery system. Given that I'm not restricting airflow, that pretty much leaves spark. I haven't yet checked if I'm getting spark, but by the process of elimination, that HAS to be the case, whether it's because the ECU is turning it off due to corrupted sensor data, or it's just plain not being generated for some reason. However, I've had my laptop scanner hooked up to it (TunerPro RT), and the MAP sensor readings look normal, the coolant temperature looks good, and other parameters I can make sense out of seem to be OK Next time it dies, I'll look to see if a code get's set.

I think there's enough circumstantial evidence at this point that if I can catch it failing to deliver spark during the stall, I'll just replace the distributor.

webbch
08-25-2013, 01:44 AM
Well, still getting the stalling. It's still entirely unpredictable, but frequency of occurence is increasing. I've been able to capture the phenomenon once while I had the timing light AND fuel pressure gauge AND my laptop running TunerPro RT. When it stalls, both the spark signal and fuel pressure seem to die off together, so it's a bit of a chicken/egg situation. I went ahead and replaced the distributor, primarily to ensure the pickup coil and ignition module are good. And just to be certain, I added a ground wire from the mount on the ignition coil back to the battery cable ground to make doubly sure that I don't have some kind of weird grounding problem. I was unable to repeat the stalling on my relatively brief test drive, so only time will tell now.

webbch
08-25-2013, 09:29 PM
Still stalling, but there's progress in the observed symptoms. This time, when it was stalling, I saw the fuel pressure dropping off while still getting spark. When it's running, I see a good strong spray of fuel from both injectors. This is in open loop mode. From what I can tell, when operating in open loop mode, about the only sensor that could affect fuel delivery (outside the ECM) would be the MAP sensor, but I see a MAP sensor voltage of about 1.4 volts at 550 or about 1.2 volts at 750 rpm RPM (has a bit over 4 volts when engine is off), and it's not jumping around all over the place. Based on these new symptoms, there's really on 3 legitimate options as I can see:
1) Fuel filter (restriction)
2) Fuel pump relay
3) Fuel pump

For now, I'm replacing the fuel filter, since that hasn't been done for a few years. The relay tested out good (hit it with a heat gun and vibration during the test to ensure the relay coil wasn't dropping out under heat or vibe), leaving only the wiring to the fuel pump and the fuel pump itself as potential problem sources if the symptoms persist.

Schurkey
08-26-2013, 07:47 AM
In open loop, every sensor EXCEPT the O2 sensor affects fuel delivery.

webbch
08-31-2013, 10:36 PM
As expected, replacing the fuel filter didn't resolve anything, so today I finally replaced the fuel pump, which seems to have resolved the issue (truck wouldn't stay running long enough to turn it around this morning), but I won't be certain until I have a couple days/weeks without the symptoms.

Old fuel pump had 3-4 ohms of resistance at the terminals. New one had 11 ohms, so I suspect the old pump may have had some shorted windings in the electric motor.

I used an engine hoist to lift the bed off after removing the 8 bolts holding the bed on and disconnecting the tail lights near the drivers side rear corner, and a couple of ground wires (also on the driver side). It really made accessing the fuel line connections a cinch.

j cAT
09-01-2013, 08:25 AM
As expected, replacing the fuel filter didn't resolve anything, so today I finally replaced the fuel pump, which seems to have resolved the issue (truck wouldn't stay running long enough to turn it around this morning), but I won't be certain until I have a couple days/weeks without the symptoms.

Old fuel pump had 3-4 ohms of resistance at the terminals. New one had 11 ohms, so I suspect the old pump may have had some shorted windings in the electric motor.

I used an engine hoist to lift the bed off after removing the 8 bolts holding the bed on and disconnecting the tail lights near the drivers side rear corner, and a couple of ground wires (also on the driver side). It really made accessing the fuel line connections a cinch.

the fuel pump will fail because of many related component breakdowns. with a vehicle this old the relay need be replaced. the ground connections all checked and cleaned, connectors also checked for any corrosion . the fuel filter replacing need be done 30-40,000 miles. but that may need to be adjusted with the fuel quality in your area. more dust/dirt this may need be done more often.

the fuel pump is a DC motor and with a lower voltage due to poor feed/ground connections this is a common failure especially with very old vehicles. low fuel levels will also cause the motor to overheat causing the windings to short out.

webbch
09-01-2013, 11:09 AM
Thanks for the info. Also, here's a couple pics I snapped to show the bed-off method of doing it:

Engine hoist holding the bed. If I did it again, I'd DEFINITELY put another strap on the bed, to avoid catastrophe if one were to break. I kinda put all my eggs in one basket on this lift - thankfully it all turned out. To straddle the middle of the bed with the hoist required me to remove the wheel on that side.
http://img.photobucket.com/albums/v708/webbch/1990%20Chevy%20Silverado%20K2500/90_ChevyTruck_FuelPumpReplacment_02_zpsdae10382.jp g (http://smg.photobucket.com/user/webbch/media/1990%20Chevy%20Silverado%20K2500/90_ChevyTruck_FuelPumpReplacment_02_zpsdae10382.jp g.html)

Here we see the fuel line connections that need to be disconnected:
http://img.photobucket.com/albums/v708/webbch/1990%20Chevy%20Silverado%20K2500/90_ChevyTruck_FuelPumpReplacment_01_zps73f0e4b5.jp g (http://smg.photobucket.com/user/webbch/media/1990%20Chevy%20Silverado%20K2500/90_ChevyTruck_FuelPumpReplacment_01_zps73f0e4b5.jp g.html)

Pulling the bed isn't too terribly miserable, but even with the hoist, it was crucial o have a spotter when removing the bed. If left entirely to manpower, I don't think I'd have been comfortable with any less than 5 persons helping (2 on each side to do the lifting, and one spotter to ensure no hangups. I have a spray-in bedliner, so that probably adds a substantial amount of weight to the bed.

I actually started to drop the fuel tank initially, but could only see the metal portion of the fuel lines that I needed to disconnect. Back at the fuel filter the lines are metal as well, so I was concerned with flexing them excessively while dropping the tank. After getting the bed off, I saw that there is actually an intermediate rubber section to the fuel lines, so partially dropping the tank in order to disconnect the lines would be possible. Still, I'd pull the bed again if I had to do it over - it's just so much easier to access everything that way. I also used a wire wheel to cleanup all the ground connections on the bed during re-installation.

j cAT
09-01-2013, 11:24 AM
on my 2000 silverado I slid the bed back about 18 inches or so then lifted up behind the cab the bed . tilting it so I had plenty of room to get at the fuel pump assy and the brake lines.

with this which many do on this style remove the rear bumper disconnect the fuel filler neck and ground wire/rear diff vent hose. the unbolt the 8 bolts holding the bed. place 2 x4 or 4x4 short pieces between the bed and the frame then slide back then tilt up. with the bed slid back the overhang weight allows ONE person to lift up the bed behind the cab.

if your vehicle were out here in the rust belt what you did would be impossible with most of this age. the bed would be so rusted out and the bolts would need a cutting.

the gm vehicles are fabricated better than fords to remove the bed.

washing off all the debris before working it is also what I did to prevent any issues. the lines can be pinched broken if the tank drop is used. the tank strap out here would also require replacing .. trucks looks good for a 1990.

Schurkey
09-01-2013, 11:27 AM
even with the hoist, it was crucial o have a spotter when removing the bed.
I popped the bed off my '88 all by myself. Didn't think a thing of it. Even left some of the cargo in place. Lifted it up high enough to clear the tires, rolled the hoist-and-box out of the garage while I worked on the gas tank. When the tank was done, Me, myself, and I pushed the hoist/box back into position, and aligned the bolt holes using tapered alignment prybars.

'Course, it is the "lightweight" version of the long-bed, with the extra-cost weight-saving perforations.

http://hbassociates.us/Fuel_Pump_1.JPG

Two things: Note that the chain is bolted around the lifting hook, to prevent the chain from sliding side-to-side; and the custom-cut 2X4 to prevent the bed sides from distorting inward.

The bolts holding the bed were the reason I bought a new impact gun. My old Snap-On IM510B struggled and hammered to get them loose. AFTER buying a new MG725, I pulled the screen out of my old gun--it's under the air inlet fitting--and found that it was 1/3 plugged with crap. Cleaned the screen and restored it's power to it's former glory.

Bolts were reinstalled with a coating of anti-seize!

webbch
09-01-2013, 03:16 PM
Nice! If I'd been able to approach it from behind, it may have been a bit easier as well. Unfortunately, my minivan that is undergoing a transmission replacement was in front of it, so no room left on the concrete :) Also, your hoist appears to have just a bit more reach than mine to boot. For me to reach the midpoint of the bed put the ram cylinder nearly up against the bed. You're right though. If I'd done my homework and done a better job lifting at the CG, I probably could've done without the spotter.

webbch
09-05-2013, 03:38 PM
It appears that replacing the fuel pump has resolved the issues I was having with the engine dying randomly. The engine hasn't died on me for the last 4 days I've been driving. It seems to be back to normal, which is great, so I can get back to working on my minivan's transmission problem :)

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