An in-cab fuel pressure gauge is a huge help diagnosing stuff like this.
CK5
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'86 Jimmy 4in Lift, 40’s, tons, 8.1 Swap- 700r4 said PNNNNN
- Thread starter GWeakland620
- Start date
This is not a dedicated trail rig, but does trailer to the destination usually. I am currently in the planning phase of doing a 52/56" spring swap, and getting back to being more road worthy.
I used to have this problem with the K10 before the TBI swap. I always thought it was cause of my in-line fuel pump right next to the exhaust. Do you have any fuel lines or pump near exhaust?
Fuel lines are ran in the factory location. Return loop is near the rear of the truck. This issue was occurring before the loop was added. I have a pressure gauge on my laptop that is hooked to the ecu.
Whoopsies, I was thinking this was another carb rig.* But either way, if you're not circulating cool fuel up to the front of the truck, where the engine actually is, then why would you expect it to be any better at avoiding vapor lock than the stock one-line configuration is? There's a reason that GM ran their recirc line off of the fuel rail, they wanted fresh, cool fuel up front, where it is most needed.
And you didn't answer either of my questions. Is this an issue that for sure affects the engine after it has cooled down? (days vs. hours) And does it ever seem to be flooding out, or does it feel/smell like a lean condition?
*Man, I can't keep very many rigs straight around here. This has got to be the most consistent thing I have talked about whenever I meet up with a CK5er. I always have some mechanical misunderstanding lodged in my brain, and then that person is setting me straight again. It's almost like these rigs are uniquely customized.
It definitely is a rich issue. The last time it died, it wouldn't start for days. It's never done that before.
What did the spark plugs look like? Any fowling? Even if it is flooding out, you should be able to dry it out and get it restarted. What sort of diagnostic data do you have available from your ECU? A realtime A/F graph would be helpful, as would capturing some snapshots of the operating conditions during the event. Since it always happens when warm, you should have O2 sensor data available.
Or, my preference, simply bring your laptop/tablet along and data log every possible parameter so you can look at everything all at once!
This is a shot of my truck at operating levels back in February. Just to show you what all I can read/see. The issue is, I'm not educated enough to really understand how to correct any wrong info.
I also have a fuel map editor, but I don't know what good values are to enter.
I. Am. So. Jealous.
If I ever get out of Dieseland, my truck is going to look like that. With twice as many gauges, at a bare minimum.
I cannot understand why some people prefer tuning carbs by feeling vs. having hard data telling you what's wrong.
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Ok, first-up, is this something that you have available while you're driving? Can you watch that A/F gauge while you're stalling out to get some concrete trends? Or even better, some hard numbers? Ditto for the fuel pressure gauge.
Don't start messing with the fuel map, making random blind changes will not help you.
Don't worry, I touch nothing until I know it's a good decision.
Yes, I can leave the laptop open and read it all. It works better with a passenger to help.
Yes, I can leave the laptop open and read it all. It works better with a passenger to help.
That's what she said!
Truth. What you want is to know what the gauges do when you're stalling. If you think you're going rich the gauges should have no problem telling you whether you're right or wrong.
I have elected a friend of mine to ride passenger for a bit tomorrow to do some reading out loud.
Do you not have the ability to record the data and review it later? That's more useful anyways, no?
I do have the ability to do a "screen shot" of the data. But again, I don't know what I am reading...
Well, a screen shot of A/F and fuel pressure would help rule out a couple of the potential causes we've discussed.
And potentially other stuff, too. If your TPS value randomly pegs while your actual throttle is at idle, going rich would be a natural result, depending on how the control logic is set up.
Get some snapshots of normal and abnormal operating conditions and look for outliers. Something will be out of place.
I guess it's time to read more.
Yeah. This isn't black magic. The ECU is deciding how much fuel to dump in based on the sensor data that it receives. If you are going rich, it will either be because some sensor is lying to the computer, or someone changed the fuel map, so the computer no longer understands the system it's working with.
The cool part is that much of the time, the computer is smart enough to tell you what's wrong if you know how to read the data it spits out.
Or, if you run a stock system, it will spit out one of those beloved error codes. Which are way more helpful than some folks wanna admit.
