I’ve got a 1990 454 SS Pickup with 114000 miles. This is the most unreliable vehicle I have ever owned. The main reason I am making this post is because the truck always dies for no apparent reason, and then proceeds to no-start for a duration of at least 20 minutes (give or take). The ECM never throws any codes or check engine light, and every single part under the hood (including a full engine overhaul) has been done in the last 15,000 miles. These symptoms are vague and difficult to describe because of the random occurrences. Sometimes I can drive the truck 30 miles before it dies, other times it won’t even make it out of my driveway. Once again I know this is all kind of vague, but I’m at a total loss on what to do about this problem. I’ve had plenty of small block TBIs and I’ve always been able to eventually find the issues with them. If anyone has any ideas on where to start, I’m willing to listen. And I am quite aware that just because the part is new, doesn’t mean it can’t break. Any help would be appreciated
454 SS dies randomly, no codes
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1. What is the fuel pressure at prime, when under load, and when the engine stalls?
2. When the engine won't re-start--it cranks but won't run (correct?) Or does it not crank? VERY different diagnostics.
3. Connect a scan tool, verify EVERY sensor and computer output including electronic spark advance, and verify that the computer is getting an RPM signal when it cranks but won't run.
4. You've replaced the distributor cap, rotor, plug wires, and spark plugs? Ignition module, and ignition coil? How about the distributor--have you checked for a broken magnet on the mainshaft? Failing pickup coil? Will the ignition coil RELIABLY fire a spark-tester calibrated for HEI, when the coil is warm and misted with water from a squirt-bottle? Ignition timing with the timing connector disconnected has been verified to be ~4 degrees BTDC? Then when the timing connector is plugged in, timing advances to 12--16 BTDC or somewhere near that?
5. EGR system verified. EGR doesn't leak at idle, opens when it should, closes when it should?
2. When the engine won't re-start--it cranks but won't run (correct?) Or does it not crank? VERY different diagnostics.
3. Connect a scan tool, verify EVERY sensor and computer output including electronic spark advance, and verify that the computer is getting an RPM signal when it cranks but won't run.
4. You've replaced the distributor cap, rotor, plug wires, and spark plugs? Ignition module, and ignition coil? How about the distributor--have you checked for a broken magnet on the mainshaft? Failing pickup coil? Will the ignition coil RELIABLY fire a spark-tester calibrated for HEI, when the coil is warm and misted with water from a squirt-bottle? Ignition timing with the timing connector disconnected has been verified to be ~4 degrees BTDC? Then when the timing connector is plugged in, timing advances to 12--16 BTDC or somewhere near that?
5. EGR system verified. EGR doesn't leak at idle, opens when it should, closes when it should?
1. I will attempt to check this
2. Correct, the engine cranks but no-starts.
3. What “scan tool” is available that will work with an obd1 and tell me all of that info?
4. All of these components have been replaced, however I will recheck everything
5. Everything involving the EGR system is new. What would be the best way to check if it is working?
Thank you
I use a Snap-On Solus Pro, purchased used from a seller on eBay. $3500+ worth of top-shelf professional-grade tool when new in 2008, for $350 delivered to my door a couple of years ago. (Somewhat more than that now--$450--$500 due to Senile Joe's economic problems, coupled to the Wuhan Plague Inflation.) Before that, I had a Snap-On MTG2500 with software cartridges covering about the same time frame as the Solus Pro--1980 1/2 to 2005. (My Solus Pro goes to 2007.) Be sure to get all the OBD1 connectors you need, GM uses at least three, plus the user manuals, cables, and various other accessories. Snap-On offered updates to the software, so the same tool might have software good to 2016 or even newer. The newer the software, the more expensive the tool is likely to be, choose wisely.
There are numerous competing products, including "new" consumer-grade tools, and scan-tool simulator software-plus-connector cable or bluetooth dongle that talk to your laptop computer. I don't trust any of that, but it's a popular work-around due to the much lower cost.
The ONLY scan tools I have actual experience with are the Snap-On units I listed.
"Replaced" doesn't mean "usable" especially with so many craptastic or outright counterfeit parts coming from Communist China.
Just as important, replacing "parts" does not fix faulty wiring between the "part" and the computer. You can replace a hundred sensors, but if the wire harness is damaged, you're not fixing the actual problem. Which is why verifying with a scan tool is much more thorough than testing a component with a multimeter--the multimeter doesn't ALSO test the connected wire harness. The scan tool shows what the computer is "seeing" from those sensors, so the wire harness is included in the diagnostics.
Again..."New" doesn't mean "Functional".
Lift the EGR valve pintle at idle. Engine RPM should drop, maybe even stall the engine. Let go of the pintle. Engine idle should recover. Disconnect the vacuum hose from the EGR valve, connect the hose to a vacuum gauge you can see from the driver's seat. Drive the vehicle, watch for the vacuum gauge to show vacuum at moderate speeds--NOT at idle, probably not at WFO throttle, but in between it should show vacuum. Depending on the computer programming, you may be able to see this just by opening the throttle somewhat, in Park or Neutral, in your driveway.
If you connect a source of vacuum to the EGR valve, it should open the valve and hold vacuum. If it doesn't hold vacuum, the valve is defective. If you do this with the engine running, the idle will suffer, maybe even stall the engine just like when you lifted the pintle by hand.
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UPDATE: I finally got someone to crank the engine while I looked at the throttle body. The injectors will spray a small amount of fuel when the key is first turned on, and once again when the key is turned off. But no fuel is spraying during cranking. Fuel pump is definitely running when key is on. The truck died in my driveway yesterday and now won’t start at all. Definitely getting frustrating
Absolutely need to verify TPS. If it's sending a faulty signal, the computer may be in "clear flood" mode, cancelling the injector spray.
And you may want to verify that the computer is getting an RPM signal; no RPM signal, no injector spray. DO YOU HAVE SPARK?
A little squirt with key on and again at key off is not something I've heard of before. Puzzling.
And you may want to verify that the computer is getting an RPM signal; no RPM signal, no injector spray. DO YOU HAVE SPARK?
A little squirt with key on and again at key off is not something I've heard of before. Puzzling.
UPDATE: as stated previously, the truck was at the point where it would not start at all. After doing some investigating this morning, I found that the coil had a corroded connection at the spark wire. After brushing off the corrosion and putting some electric grease, the truck starts with no problem. Apparently with these TBIs, if the truck doesn’t have spark, the ECM will tell the injectors to not spray fuel. I definitely feel a little stupid for not realizing this earlier, but we live and learn. I will do a road test within the next few days and see if there are any issues.
Yes you are correct about checking the spark. That ended up being the problem. Also I looked into those scan tools you recommended. Definitely is something I need to invest in. Thank you for telling me about that. I didn’t know there was a tool that could read OBD1s
Common misconception.
I posted a thread on another forum that discusses the info available from my '88 K1500 using the scan tool I used to use. MOSTLY, the info available on a proper scan tool is dependent on the vehicle computer. The older the computer, the less info is displayed, and the slower the refresh rate. But even in the first years, all the sensor data was available along with codes except on Chevettes which had a genuinely craptastic computer system (MIN-T system.)
Anyway, this thread shows what's available on my '88, in posts 14 and 15, but the whole thread is kinda humorous.
94 k2500 no low end power and horrible fuel mileage - Automotive Forums .com Car Chat
94 k2500 no low end power and horrible fuel mileage C/K
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