Engine miss, no miss codes

[S10Fan]

97 Yukon, 5.7, 4L60, 2 door, 2 wheel drive.

Began missing under load, idles fine, the miss is bad enough I've parked it for the time being.

Checked plugs and wires, all were new anyway, no issues, the plugs look new after 3 months.

Fuel pressure at the rail is 52-60, holds 50 after shut down, holds it for quite a while, no fuel smell anywhere, not at the motor or tail pipe. Truck starts and idles fine. On 2 different occasions at startup the motor spit back at the throttle body, the second time the spit back was bad enough to blow the plastic PCV valve at the intake. I replaced the PCV, hasn't done it since.

New Cam sensor and distributor assembly, old distributor case was cracked at the cap screw hold down.

New crank sensor
New TPS
New IAC

I'm not a guy that just throws parts at a vehicle, all the above stuff, except the distributor, were purchased new from someone that never used them, all the part numbers matched my truck cheap, real cheap. All the above parts were replaced long before this miss issue came along.

The only codes are for the cam position sensor, these codes have been present for over a year after the distributor swap. I used a Snap-On 2500 scanner to set the distributor and never could get it within +- 2 degrees per spec. The truck has run awesome anyway, so I really don't see the CPS code being the issue.

Any input is much appreciated. I'd love to do a 5.3 or 6.0 swap but my bank account says otherwise at this time. LOL

[speedygonzales]

Originally Posted by S10Fan

All the above parts were replaced long before this miss issue came along.

Since it seems based on what you said, that the parts have been in there a while. Have you looked at the condition of the inside of the distributor cap and rotor?

I don't usually get even 2 years out of mine. In fact this past Dec 26th as we were going to visit fam, it wouldn't start. Previous day started and ran fine.

In years past it would crank longer and longer before firing up as it got worse and worse.

Also, even though you checked the FP, have you changed the fuel filter? I can easily see where if it were restricted, it would idle fine but not allow enough fuel during a load.

[S10Fan]

Originally Posted by speedygonzales

Since it seems based on what you said, that the parts have been in there a while. Have you looked at the condition of the inside of the distributor cap and rotor?

I don't usually get even 2 years out of mine. In fact this past Dec 26th as we were going to visit fam, it wouldn't start. Previous day started and ran fine.

In years past it would crank longer and longer before firing up as it got worse and worse.

Also, even though you checked the FP, have you changed the fuel filter? I can easily see where if it were restricted, it would idle fine but not allow enough fuel during a load.

Fuel filter......Yes, changed it about 3 months ago, nasty inside, changed it again a couple weeks later, everything was clean.

I'll look at the cap and rotor this weekend.

[speedygonzales]

Any updates on this problem?

[S10Fan]

Cap and rotor looked good. I ordered a new fuel pump that should arrive today, AC Delco. Pumps on the 2 door versions mount to the sending unit but are separate of the sending unit assembly, much cheaper. Anyway, checked the pressure with another gauge that read a little lower. Further research shows the required pressure to be 56-62, mine falls in the 50-60 range. If nothing else I'll know the fuel pump history after the swap. Also planning to cut an access door for me or the next guy.


Thanks

[speedygonzales]

Br careful with pressure numbers. Most are primed but not running. Running for the ones that prime are lower.

[Kudzupatch]

My experience is limited to TBI but I will share a couple of things I ran into. I had a miss but it was always at idle or just off idle. About pulled my hair out finding it. I had a combination of problems.

Bad injectors. One of mine it turned out was bad and running very lean. Found that watching the computer readout hooked up to the car. Saw the lean condition along with wildly high knock counts and finally figured it out. Maybe you have a clogged injector?

As Speedy said, I had ignition problems too. New ignition modules going bad. New Caps (yes 2) failing. All this really complicated finding the root of the problems. Lesson learned was NEVER trust new parts. Especially aftermarket!! GM parts have not given me any issues.

My new plug wires turned out to be the near impossible to find problem. Plugs looked great, wires looked great. Finally one day after 8 hours on the road the miss got really bad near home. Pulled in the garage, popped the hood and I could hear an intermittent spark at at one of the two rear plugs. Next morning it was fine and went back to an occasional miss. New set of AC-Delco wires fixed it and the old set (3-4 months old) looked perfect when I removed them. Runs perfect now.

[speedygonzales]

And as Kud brought up, ignition items. Wires themselves can be an issue and sometimes a look at night will show what I term as "side firing". Where the spark comes out of the side of the wire. Some times it requires a mist of water from a spray bottle to find it.

Also on Vortec 5.7's the coil is a tune up item. It should be replaced every 60K miles. If you have the OEM look at the coil and see if it has tell tale white dots on it. That for sure is bad but then a look at night would see it as well.

I have found the ICM that is mounted to a plate comes from the factory with heat sink compound behind it. After a while this compound dries out. It is a good idea to clean it off and replace the compound.

Look at the plugs at night too. Sometimes you can have flash over where the spark goes on the outside of the plug to the base of the plug. The ribs are made on the plugs to reduce this problem but as the conductor in the plug wears, this is easier to happen.

[S10Fan]

"If you have the OEM look at the coil and see if it has tell tale white dots on it."

Where? I assume inside the terminal where the coil wire connects?

[speedygonzales]

No on the sides of the coil windings.

Oh and don't ask me why I didn't notice until now that you are from NN. Duh I feel stupid. I would ask you over but if my son sees your 2 door yukon he'll bug you to buy it.

[S10Fan]

Changed the pump yesterday, installed an AC Delco unit, no change. The old pump was missing the strainer and the pickup was packed with trash. I thought for sure I'd found the issue, nope, no change.

I'll check the coil over the weekend, already ran the truck at night looking for spark issues, nothing.

Speedy........I'm planning to sell this truck once I track down the problem, but, a friend of mine has first refusal.

[Kudzupatch]

Originally Posted by S10Fan

Cap and rotor looked good.

Probably not your issue, but the two caps I had fail looked good. Out of desperation I checked the Ohms on each tower. What I found both times was a faulty connection at the coil tower. I would get off and on readings as I pressed down the connector. First time I was just desperate when I tried this and found one of my problems.

[S10Fan]

Thanks for all the replies!

Speedy........Is this a white spot?

BTW, my coil is still riveted, original I'm sure, 18 years old, 250K miles

[speedygonzales]

Could be, I've never seen one that big. They are usually the size of a pin. Look at it at night with no light around and see what's arcing.

Definitely replace it even if you get a cheap auto parts store replacement. You have to grind the rivets off and replace them with screws. Do the ICM heat sink compound also.

Please let us know what happens after you change it.

With regard to the pump, I knew your pressures were ok if that was running pressure. I have a pressure gauge mounted on my "A" pillar so I can check it all the time.

Just FYI if you still have the OEM style poppet style injectors the pressure is designated as 60-66# and if you have the replacement MP injectors, they are designated at 55-62#. Those pressures are always after priming NOT while running.

[S10Fan]

Coil change, nothing, still the same.

I'm done for a few days, LOL

[speedygonzales]

Originally Posted by speedygonzales

Do the ICM heat sink compound also.

When you get a chance, pull a plug wire while it's running to see first, if it runs crappier and 2, if it sets a SES.

[S10Fan]

Yes, I did add fresh heat sink compound.

[speedygonzales]

Well?

[S10Fan]

Deactivated the plates, dropped the insurance, and parked it at a buddy's shop. I don't have time to mess with it right now, and to be honest, it might sit for a while. I told my buddy to play with it when he has time. The guy I bought it from is interested in it to do a 5.3 or 6.0 swap, I might send it away as it is.

Too much going on with the family right now.

Thanks to all for your suggestions/help.

[speedygonzales]

What's it worth to sell?

[S10Fan]

The guy I got it from is a very good friend and would get first refusal. With it parked/off the road it isn't costing me anything to own it. With the truck being 2-door, 2-wheel drive I won't have any problem at all selling it, of course the price will be directly related to how well it runs or doesn't.

The goal now is for my friend to look at it with a fresh pair of eyes and see what he can find. Sucks, that thing doesn't burn a drop of oil, has a new trans mission (3 years ago) and ice cold A/C.

[68C15]

I'd be hooking up that MT2500 and looking at data. Primitive scanner but still functional

[S10Fan]

Originally Posted by 68C15

I'd be hooking up that MT2500 and looking at data. Primitive scanner but still functional

Planning to, just as soon as I can borrow it again.

[speedygonzales]

Your welcome to hook up to my Solus Pro

[S10Fan]

Update........... Picked up a known "good" fuel spider, the updated version. Installed the spider along with new upper intake gaskets, no change.

Planning a compression check next weekend if time permits.