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Discussion Starter · #1 ·
Hello everyone,

Recently did a head-gasket and intake gasket replace on my '99 buick park avenue, natural aspirated. The intake gasket was cracked/corroded from dex-cool eating plastic and the back head had plugged coolant ports from bad coolant maintenance from the previous owner. All seems well and good for those gaskets now, it is no longer sucking down coolant, and my compression ranges all between 155/165 with no evidence of head warp.

Besides gaskets I threw in new iridium plugs, ACDelco wires and 3 new coil packs as well as a new upper intake plenum and evap canister valve. The ERG valve is almost new, but the pipes had hairline crack on manifold and intake so I did "the nickle trick" and plugged the intake side so I could see if that was causing a vacuum issue but it didn't seem to matter much if at all.

I am using toque lite on my phone with an OBDlink for data, and have noticed wild ft1 and stft fluctuations, quickly bottoming out on the graph in a negative spike before returning to a more normal trim right after, but I have seen MAF and RPM do the same, though not as often, so I question the accuracy of that data. My vacuum using the app seems to hold around 16.6hg/in.


It doesn't seem to throw the p0300 code as much until it is warm or until I hold it at a higher RPM, it idles rough and has a bit of a hard time starting, especially warm, even giving me a backfire on occasion. I pressurized the fuel rail with the fuel pump with the injectors out expecting drips but didn't see any.

My next guesses are ICU, fuel pressure regulator, injector(s) and/or cam position sensor, but any thoughts or help would be appreciated.

Thanks
 

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Stop buying random parts. I'd put the original coil packs back on there, and eliminate much of the random non-OEM electrical components you just introduced to the system.
 

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Discussion Starter · #3 ·
Stop buying random parts. I'd put the original coil packs back on there, and eliminate much of the random non-OEM electrical components you just introduced to the system.
Well, I don't think non-OEM plug wires with melted boots, the bad coil pack, the fouled from coolant non-iridium plugs and the cracked purge valve and the melted upper plenum were doing me many favors, but thanks for the suggestion.
 

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My favorite part about answering technical questions with partial information is when replies come back with more partial information that makes a logical analysis of the initial info seem absurd.

Now we discover that you have a car with an extensive list of pre-existing issues and broken components, possibly from a fire or accident that may have undiscovered/latent issues you haven't found, yet (shorted/broken wires inside a harness, corroded/missing ground wiring, etc.). These are the types of repairs that are not often standard and require thorough digging and iterative (step-by-step) testing by someone in person, which would take forever to walk through online.

I'm doing exactly this on a '96 Camaro right now, because the previous owner used a ratchet strap to restrain the broken transmission mount, rather than install the $20 replacement part... This is probably causing the short I'm finding on the O2 sensor circuit which has a harness pinched by this garbage. Not a standard issue that you can discover easily by just saying the 20A fuse for the O2's & MAF keeps popping. Still no guarantee that I find the spot where the harness is shorting without fully peeling back everything, but it's an in-person job that's unique to the car and what happened during it's lifetime. (Analogy over)

TL;DR - If you see how many people are tossing out good parts for questionable replacements here, you can tell that cautioning people to take their time to troubleshoot with their head before their wallet is important. When obviously broken components aren't included in the post, I can't be Professor Xavier and know what the remaining fine details are on your end.
 

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Discussion Starter · #5 ·
I mean, I said what was replaced, and it was replaced because it was broken. Granted that folks toss good components and don't always use the best judgement on replacements, but you could just have easily asked instead of assumed. I bought the car sight-on-scene (for what I thought at the time was a good price at the time) and it had the P0300 when I bought it. I thought the intake gasket and the common upper plenum exhaust melt were the culprits, and they were, but have since discovered the rest as I dove in for the head gasket, which I figured plugged from the over-heated plug wires on the right motor side. Now I'm just hoping to get it to daily driver status and figure out more before I do buy something else because I've run out of obviously bad parts and want to avoid the part roulette and wasn't sure what else I should test or how to test it. I did pull off the ICU, clean the contact plates, and checked the grounds. The car hasn't had any serious problems, no accidents, no fires, no salt road exposure or rust. Cheap plugs, cheap plug wires, cheap mismatched coils with one having a big CHINA stamped on(not the bad one, funny enough), dirty coolant probably rarely if ever changed. I figure it mostly just suffered from a cheap owner.
 

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The onus is on the person posting a fresh request for help to explain the issue as thoroughly as possible, because we want to help, but can't effectively do that on partial information.

Now, you have multiple posts with a rat's nest of storyline and useful explanations scattered around. At least it's all there now, but I can't always be expected to either ask 20 unrelated questions to extract the full story, or prod you about the approach that's seemingly indicated by your introductory post until we finally hear more that may guide talk towards actual results (we chose #2).
 

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Discussion Starter · #7 ·
The onus is on the person posting a fresh request for help to explain the issue as thoroughly as possible, because we want to help, but can't effectively do that on partial information.

Now, you have multiple posts with a rat's nest of storyline and useful explanations scattered around. At least it's all there now, but I can't always be expected to either ask 20 unrelated questions to extract the full story, or prod you about the approach that's seemingly indicated by your introductory post until we finally hear more that may guide talk towards actual results (we chose #2).
Okay, so you assume I replace parts that don't need to be replaced. I tell you that I replaced them for real reasons. Then you assume that the car must have had extensive damage. I explain further why I replaced the parts I replaced and that there has not been extensive damage. All of which could have been inferred from the first post had you not assumed that I hadn't done my due diligence before making my post, or had asked if you had doubts. Now, with no real new info added, all the info is here, "in a rat's nest" just to explain why I replaced what I replaced. Okay, good. You can actually help with cars now?

I'm leaning heavily towards ICU. It gets hot, things start getting worse and all the heavy resistance from bad coil, wires and non-oem plugs has been known to fry them.
 

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99% of these cars have run non-OEM plugs since they hit the market. That's not a typical source of issues in this platform, and if it was, millions of these cars would have been dealing with it for decades.

I'm thinking whatever madness caused the car to be so borked may have affected the wiring harness (continuity testing, tracing/inspecting, etc. will be key there). At minimum, you can get fresh, inexpensive OEM ignition components from a upull yard with careful selection. This is going to be a hunting expedition, since prior damage and problems aren't clear, and the extent hasn't fully been explored.

As for your huff about thinking you gave enough half-truths to let people infer solutions, that isn't a healthy way to get expedient answers. Relate it to pulling up to a drivethru and saying you want the $9.99 meal with a Coke, and immediately pull up to the window, and get upset when you either get something you didn't want or get asked for more clarification.
 

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Discussion Starter · #9 ·
I don't think the non-OEM caused the problem, I figured they and the wires were bad because of the overheating and coolant fouling from the gaskets and once bad they could cause other problems. I pointed out that they are good quality and new because it is usually the first question raised when asking about a P0300. I scoured the forums pretty well before making my post, and I have heard of them damaging other electric components once they go bad, such as coil packs and *ICMs (I've been accidentally been calling them ICUs). As of right now, coils to plugs all test good, but could still be an ICM problem. It could be a wiring harness problem, but I i haven't seen any indication with much of that being tampered with or damaged and my data coming from modules on the harness seems fine, MAF, vacuum, etc, albeit with the odd dropout. Though I thinking that could be my OBDII bluetooth connection doing that. I'm still leaning ICM way because the way it changes with heat, but I've got more tests to run for injectors and fuel pressure when I have time before I commit to dropping $120+ bucks on one willy-nilly.

As far as analogies go, I ordered a number six with large fry and coke and had a shake and onion rings given to me because that's what everyone else orders.
 

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Glad we're bringing the analogy plane in for a soft landing. I'll probably re-read up top later on to get a better idea of what was/wasn't relayed, and try reading into what you're saying some more.

If it's a transient issue, I would really try cleaning up all the connections, especially the grounds below the coils and above starter, and at the battery-to-frame cable. Adding a "rewire" for a solid engine-to-chassis ground is also cheap via store battery cables, along with getting dielectric grease in all the connectors as you're in them.

These computers are pretty good at identifying specific cylinder misfires (0301-0306), so when it's 0300 and can't pin it on specific one(s), that's usually pointing slightly away from the ignition's individual items for cylinders. Sometimes it's a fueling/vacuum issue that's started degrading, sometimes it's a cam upgrade causing sporadic firing on purpose for us upgraded folk, as an example.

For crank/cam sensor signals, you should be able to log the RPM signal to see how consistent it's reporting a normal value without dropping out. I've logged with the Torque app before, with mild success, but not sure which other freeware for the ELM may provide some outputs to review after real-time viewing.
 
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Discussion Starter · #11 ·
Glad we're bringing the analogy plane in for a soft landing.
🤣
Thanks for the advice. I would also like to say I'm sorry. My tone has been crap for someone asking for free help.

I'll check my grounds, clean up my contract points and check out my RPM. I have noticed a drop out in my RPM before on Torque on my graph, but the motor isn't actually following suite. I figured at the time it may be a bluetooth connection issue since my fuel trims and MAF also have also dropped out, but I think now I'll give it a closer inspection.
 

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Discussion Starter · #12 ·
Update: Got a hold of a better scanner, showed misfires occurring on cylinders 2 and 5. Tried a known good coil pack, and swapping coil packs, no change. Ordered SMP brand ICM, slapped it on, runs like a top, no code.

Why they decided that the computer shouldn't throw a PO302 and P0305 as well as the P0300, I'll never understand.

Also did a CASE relearn because the computer could do it and I didn't know when it was last done and might not be able to as easy later.

Thanks for all the help.
 

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Gotcha, hope it behaves for you. I'll be chasing a bad running one for a coworker, and will have to dig into the spare parts pile to swap some of those items, as well.
 
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