The tips look well worn and would like to know how many miles they were in the engine. Also, did you do a compression test while apart?
98 Tahoe - Cylinder 6 misfire - fuel or ignition problem?
- Thread starter HoeLV
- Start date
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Those plugs came out after about 50k miles
About 50k, probably a bit under. No compression test, don't have the equipment. Considering getting a kit. Is this one worth while? Anyone with experience with it here?
Compression Test Kit
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For at least a one time test, the HB kit should be fine.
I ran compression test this morning and everything looks good to me. I checked each cylinder twice, results below:
Cylinder 1 - 165 | 165
Cylinder 2 - 169 | 170
Cylinder 3 - 167 | 170
Cylinder 4 - 170 | 168
Cylinder 5 - 170 | 167
Cylinder 6 - 160 | 165
Cylinder 7 - 164 | 172
Cylinder 8 - 173 | 170
All the plugs still look good, didn't take a picture as they all look the same and as expected with only 450 miles on them.
What would you suggest looking into next? Cylinder 2 still has a consistent misfire and all the others seem to be fine. The only misfire code is cylinder 2. I can check to verify what the others are showing in history.
Thank you for the assistance!
Possible vacuum leak.
east302
Full Access Member
So the misfire moved to #2 after the new work?
I haven’t had any issues with the two Delco (made by Dephi) MPFI kits, but every now and then you’ll hear someone have issues with other brands. It’s probably like most things - people only say something when it’s broken.
If you can rule out the ignition (swap parts with other cylinders and see if it moves) then that may be the way to start. To me, odds are low that your new Delco parts are bad out of the box but anything could happen.
They do sell an injector balance tester but I’ve never used one. It should compare all eight pressure drops as each injector is opened, presumably from the Schrader valve at the intake. I’d think that all eight should be about the same within some tolerance level, so any outlier would stand out.
Any issues with starting? A fuel pressure test wouldn’t hurt to see if you’re losing pressure (leaking injector).
Last, once the injector was seated did you take it back out? They barely clip in to begin with so it is tempting to try moving them around a bit. Per Delco, once seated they shouldn’t be removed lest the clips break.
I haven’t had any issues with the two Delco (made by Dephi) MPFI kits, but every now and then you’ll hear someone have issues with other brands. It’s probably like most things - people only say something when it’s broken.
If you can rule out the ignition (swap parts with other cylinders and see if it moves) then that may be the way to start. To me, odds are low that your new Delco parts are bad out of the box but anything could happen.
They do sell an injector balance tester but I’ve never used one. It should compare all eight pressure drops as each injector is opened, presumably from the Schrader valve at the intake. I’d think that all eight should be about the same within some tolerance level, so any outlier would stand out.
Any issues with starting? A fuel pressure test wouldn’t hurt to see if you’re losing pressure (leaking injector).
Last, once the injector was seated did you take it back out? They barely clip in to begin with so it is tempting to try moving them around a bit. Per Delco, once seated they shouldn’t be removed lest the clips break.
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The first 400 miles after all the work, ran perfect. Then with the flip of a switch it seems, cylinder 2 misfires almost constantly. I could swap the plug and wire with another, but just doesn't seem likely. They both look fine, feel fine and are brand new.
Truck fires up instantly every single time. It never used to start up so quickly.
I'm debating on replacing the distributor. What are the thoughts on a reman AC Delco vs new? You can get both from rockauto.com
east302
Full Access Member
My best guess is that it’s one of your new parts since your old symptoms went away and a new one appeared.
Something isn’t right at #2 - fuel, spark or air. I’d put air to the side given the compression test and your lack of an issue at that cylinder before the ignition and fuel part changes. Spark could be checked by swapping the plug, then the wire or just start with a spark test - comparing the spark quality with non-misfiring cylinders. It really could just be a bum cap; even the Delco plant probably has off-days.
Fuel would be either the injector pressure drop test or a general pressure test. If you aren’t having trouble starting it, that may rule out a leaking injector.
The only aftermarket distributor that I’ve bought (and I think you should save your money on that until you check the ignition components) was a Summit brand since it had metal cap screw tabs versus the plastic ones that like to crack on the stock ones. The distributor itself was fine, but their cap failed within a few weeks and caused a misfire on cylinder three so bad that it wouldn’t start with that plug connected. It’d start and “run” on seven cylinders, just not eight. A Delco cap fixed that.
As for new versus reman, I’d pick new on just about anything that required any effort to replace if it was bad out of the box.
I’d probably do the spark test first.
Something isn’t right at #2 - fuel, spark or air. I’d put air to the side given the compression test and your lack of an issue at that cylinder before the ignition and fuel part changes. Spark could be checked by swapping the plug, then the wire or just start with a spark test - comparing the spark quality with non-misfiring cylinders. It really could just be a bum cap; even the Delco plant probably has off-days.
Fuel would be either the injector pressure drop test or a general pressure test. If you aren’t having trouble starting it, that may rule out a leaking injector.
The only aftermarket distributor that I’ve bought (and I think you should save your money on that until you check the ignition components) was a Summit brand since it had metal cap screw tabs versus the plastic ones that like to crack on the stock ones. The distributor itself was fine, but their cap failed within a few weeks and caused a misfire on cylinder three so bad that it wouldn’t start with that plug connected. It’d start and “run” on seven cylinders, just not eight. A Delco cap fixed that.
As for new versus reman, I’d pick new on just about anything that required any effort to replace if it was bad out of the box.
I’d probably do the spark test first.
I will swap plug and wire tomorrow, see what happens, although not often new part could be defective.
I picked up a fuel pressure test kit today, so I will check that tomorrow as well. I presume for the fuel injection drop test is different than standard pressure test?
