Hey all, so after years of lurking on the forums and countless answers to all my problems, I'm at a loss with my current pre-detonation situation. I'll start with the current state / symptoms and then follow up with what I've done to battle this issue.

First off, I drive a 1991 Pickup 4 cyl 22RE w/ 31" tires and 4.11 differentials. The pinging used to only happen going uphill in 4th gear and sometimes in 5th if there was a slight incline. It has gotten so bad that it happens in second gear going up slight inclines and even just getting into first gear from a stop has become more difficult with the engine almost wanting to stall out unless I give it a lot of gas and ease off the clutch slowly. The other symptoms that may be related include general power loss (can't really go over 65/70 without the engine pinging terribly) and major pressure build up in the gas tank. Here's a detailed list of things I've done/check to try and fix the pinging:

Timing - Replaced TPS, timing chain, and guides. Set timing to 0-2 degrees jumpered which helped the problem slightly. Currently set @ 5 degrees jumpered and the pinging is terrible. I will be setting it back to 0-2 degrees just to provide a little relief.

Gas - Running 91 Octane fuel from Chevron (in California). Before the issue got as bad as it is in its current state, I could add some engine knock additive to "cure" the problem temporarily (car still ran super sluggish).

Fuel Delivery - Replaced fuel filter with an OEM filter. Tested fuel pressure @ cold start injector and it checked out perfectly. Replaced all 4 injectors with rebuilt / flow tested injectors (this was my most recent "fix"). Gained a ton of power right after replacing the fuel injectors and the pinging went down significantly. Its been two weeks since I replaced the injectors and the power has decreased worse than ever and the pinging is the worst it has ever been. I have a suspicion that there might be a ton of crud in my gas tank that is clogging my injectors. My mechanic said the old injectors had a ton of ˟˟˟˟ on them.

Exhaust - I haven't replaced anything on the exhaust system but I have measured the inlet/outlet of the catalytic converter with an infrared temp gun. The inlet after a nice freeway trip is at about 550 degrees F and the outlet ranges from 450-515 degrees F. My truck passed smog with flying colors so I've been hesitant to just swap out the catalytic converter until I try everything else. Oh, did I mention I banged on it and nothing was rattling.

EGR - I tried blocking off the EGR for a test drive and this didn't seem to help either. There is still the possibility that the EGR is maybe stuck somewhat closed and this would increase combustion temperatures / cause pinging.

Engine - Valve job performed in the last 1k miles. Oil changed in the last 1k miles. Cleaned out combustion chambers with 3 servings of seafoam through the air intake as well as spraying carb cleaner directly in the combustion chambers and shooting it out with the starter motor before firing it up. This significantly cleaned the carbon and I visually inspected with a scope. My compression on all 4 cylinders ranges from 167-184. New spark plugs, distributor cap, and wires.

Air Intake - New air filter. I haven't messed with the AFM at all yet as I suspect the issue lies somewhere in fuel delivery or combustion temperatures (carbon / blocked egr).

Cooling - New radiator. New coolant temp sender. New T-Stat. The car never overheats or even comes close to it.

Vacuum Leaks - Found a couple of small leaks and fixed them. Smoothed out the idle slightly but the pre-detonation still persists. Had my mechanic look for leaks as well and he found another small one and fixed that.

I have a mechanic friend that is coming over next week to help me look at some stuff like the EGR, Gas Tank, etc. I will keep you guys posted if anything develops. Any ideas or insight would be greatly appreciated! Let me know if you have any questions.

EDIT FOR FIX: Experiencing probs again see post #20 for update

FIXED!!!!! AT LASSSST! I'll update my main post as well to make it easier to find but I had a slew of issues and I as of this week managed to correct them all.

Fixing the ping / pre-detonation: Turns out it was the carbon build-up on the piston crowns that was getting hot and causing the gas to pre-detonate. I'm sure the other things I did along the way helped for the most part (replacing fuel injectors, tps, timing chain, checking all the sensors, etc. see main post). I ended up taking the head off the engine and scraping all the carbon off the piston crowns. I also took the plenum and intake manifold to a machine shop to get thoroughly cleaned. This job was a PITA and I ended up snapping a head bolt, breaking my already replaced timing chain guide, and having to replace exhaust manifold posts). After all this and putting the engine back together...NO MORE PREDETONATION!!!! I was still having an issue with hard warm starts after all this.

Idle Issues / Hard Warm Start: For the last two years I've been having issues where my car would not want to start easily after I had driven it and let it sit for 30 minutes or so. I'd have to blip the throttle and the issue kept getting worse and worse. One day on the freeway my car died on an offramp because it was idling at 100 rpm. I could pretty much rule out IACV because I had already replaced that when I bought the truck 4 years ago. When I checked my freshly adjusted idle screw, it was completely bottomed out. The o-ring was so worn out the idle screw would get sucked to the bottom 5 minutes after I started driving. Replaced the idle screw and my idle returned to somewhat normal (still had warm start issues). After scratching my head for the last year about the warm start (felt like I double checked literally every possible culprit), it turns out that I was having a vapor lock issue. Replaced my aftermarket gas cap with an OEM gas cap and have seem noticeable performance increase and no warm start issues. For something so simple I literally wasted a good chunk of my life diagnosing and thinking about this problem.....

TL;DR
Taking the head off my engine and cleaning all the carbon from the piston crowns and intake fixed my pre-detonation issue. Replacing the o-ring on the idle adjust screw and replacing an aftermarket gas cap with an OEM gas cap fixed my hard warm start issue and gave me much more consistent performance after the car was hot.

 

No codes?

Did you test / replace the knock sensor?
It's wiring to the computer? (Pin)

 

No codes. I did test conductivity to the knock sensor from the ECU end to the sensor to make sure the wiring wasn't messed up and it wasn't. I've heard the sensor itself is pretty robust and doesn't typically break since its just an acoustic sensor. I also made sure that it was in the right spot according to some diagram I found on these forums.

 

You certainly should remove the cat and determine that it is not plugged. You should be able to see through it.

 

Wow, you sure have ticked all the right boxes, we know what you drive, what you did, what the truck does.
the quote above is the closest thing I see to a smoking gun in your whole post. If you suspect crud or water in your gas make sure to eliminate that as a possibility, drain the tank, clean it out, put fresh gas in, replace the fuel filter, maybe even put a second one in that is clear so you can see junk in it and put it where you can swap it out easily, run the fuel pump with the line into a pan after you put fresh gas in it so you get the bad stuff flushed out then hook it up to the filter and try running the engine.
Good luck.

 

Flow test the fuel pump at the return line from the regulator.

How's your oxygen sensor?

Has it progressed to rod knock from predetonation?

 

If your cat is plugged it will get very hot. It will also pass emissions tests.
Put a vacuum gauge on it and compare readings here.
https://www.google.com/search?q=vacu...4OgWtJC3D4EpM:

 

Wow! Thanks for all the super useful responses! As far as the cat goes, I can't remove it because it's welded on. I can also feel the heat from the cat on my legs during long drives. I have some time on tuesday so I'm definitely going to drop the gas tank, blow out the fuel lines and inspect/clean (maybe send out to get recoated if dirty?). I'll also vacuum test the cat for back pressure. I will keep you guys posted as to what I find out! Thanks again! Maybe chasing this pre-detonation issue is a blessing and a curse because I sure as ˟˟˟˟ know a lot more about my truck now.

 

While you are doing vacuum test, pull a vacuum on the EGR valve, and listen to see if you can hear the diaphragm working back and forth with vacuum on and off. Have you checked EGR to see if it's clogged? They get very clogged over the years.

 

Definitely on my to-do list. The only test I've done is to block it off to make sure it's not stuck open. Will tackle this as well as the gas tank inspection and back pressure test tomorrow.

 

Checked the exhaust back pressure as close to the intake manifold as I could and it performed completely normal. 20" at idle. Dropped to 5" when revved to 3k rpms and rebounded to 21" quickly. I also checked the EGR valve with a vacuum gauge and its opening and closing properly. Just dropped my truck off to have the tank inspected and potentially recoated. We'll see where to go from there once I get a call back from my mechanic. In my opinion, it has to be a fuel delivery issue so I'm going to try to attack it from the source and work my way through.

 

I would all so recommend removing all of your belts and see if you can spin the harmonic balancer. The outer portion will spin free from the inner portion. The timing mark is on the outer ring. So what you think is 5 degrees may be way off.

 

Sorry for the delay! Got my truck back from the shop. The good news...the pinging is gone...and they didn't charge me a dime! The bad news...they had my truck for two weeks and they still haven't even told me what they did to it. From what they have told me is that my gas tank looked fine so I know they checked that out. They had my truck for two weeks and brought in pops to take a look at it / tune it since I believe they were kind of scratching their heads on what was going on. From my conversation with him, the things he mentioned were that sometimes when you replace fuel injectors, the O2 sensor / ECU reacts at seeing more fuel go into the combustion chambers and reduces the pulses. I checked my timing to see if they did anything to it and it seems as if maybe they knocked it back from 5 degrees to 3-4 degrees. I bumped it back up a little just now and will test ride. I'll try and get a more definitive answer about what they did but so far it seems pretty good. The only complaint is my top end seems slightly limited so I'm hoping by bumping up the timing a little bit will get it back to where I remember. Otherwise the torque seems good as its ever been and no pinging even on uphills in 4th.

 

I had a 94 22re pickup that used to ping badly while wheeling. I switched up to 89 octane gas, much better. But it came back driving on highways (using 87 octane), took it to dealer.... The mechanics said that "light ping" is okay, go figure!

 

So, I've driven around for a while since I got my car back from the mechanic as well as talked to my mechanic. I definitely still have a ping under load but it seems to be more intermittent in severity. Some days the ping is bad just like before and other days its a light ping. I also still have a problem with my car either not starting or idling very low/rough when warmed up unless I gas it briefly. My gas tank was inspected as well as the fuel return line and the fuel was even tested. All of that turned out to be fine. My mechanic believes its an electrical issue because it seems to be intermittent. Some days my truck seems to have some pep and others it seems to be really sluggish and pinging. I've gone through and tested my TPS (even though it is brand new) and it was perfectly to spec. My next suspicion was the ECT sensor as I've had to replace my gauge temperature sender and the guy I had bought the truck from put stop leak in the radiator and effectively ˟˟˟˟ed most of the cooling system (replace heater core, etc.). It tested out fine at its cooled down temp (~75 F) but I still have a suspicion that it might act weird at higher temps like my gauge temp sender did (would randomly spike super hard into the red when at operating temperature). I also decided to test the AFM according to this guide (http://www.4crawler.com/4x4/CheapTri...html#Operation). Everything checked within range EXCEPT test 1 of static tests had a higher resistance to test 2 and it is not supposed to. Also, I could only get a brief resistance value of 1.8k from test 4 (temperature probe. air temp was 65 F) and then it would immediately go back to thinking there was an open circuit (infinite reading).

Does anyone have experience with testing the AFM and is this slightly normal behavior? My next step would be to try to find one that tests within spec at the junkyard and throw it in my truck. My other question is whether my O2 sensor would be guaranteed to throw a code if something was wrong with it? Any suggestions would be greatly appreciated! Also, I still have plans to test the harmonic balancer if all the sensors test out fine. Just figured this would knock a few more questions off the list.

 

minor update: O2 sensor checked out just fine according to FSM and the ECT sensor seems alright (assuming it doesn't spike when I drive). I measured 220 Ohms after running my car up a hill real quick (IR temp gun measured 195 on the coolant hose). I'm starting to suspect the AFM as it is the only piece of equipment that hasn't checked out entirely to spec. I know the temperature probe is important in calculating the mass of the air passing through the AFM so I imagine this could be sending some false readings to the ECU if it isn't working properly. Any insights always appreciated.

update again: Checked the AFM resistance values at the ECU plug as well and I was actually able to get a good reading for the temp probe but the E2 - Vs resistance value is 200 Ohms out of spec at the ECU while it was barely in spec when testing at the AFM. The guide to checking the AFM says that the resistance for E2 - Vs should be less than E2 - Vc so I'm still wondering if that could be an issue. I also retarded my base timing to 3 degrees (jumpered) after talking to another mechanic. He said that there was an internal bulletin between Toyota techs saying that there was an issue with the internal programming of the ECU where it would over advance timing on accel / partial throttle. Their fix was to retard timing to improve performance. I'll drive with it at 3 degrees for a little and see if that helps.

 

So to follow up, the other day my car would immediately die after the engine turned over even when I opened up the throttle. The only way I was able to get my car to start was by resetting the ECU. What are the chances I have a bad ECU given everything else I've done? It seems as if the ECU is changing my air/fuel mixture every couple days and the car changes the way it runs constantly. Also, it seems like my ECU is over advancing the timing. @ 2500 RPMS I'm getting 38-40 degrees.

 

FIXED!!!!! AT LASSSST! I'll update my main post as well to make it easier to find but I had a slew of issues and I as of this week managed to correct them all.

Fixing the ping / pre-detonation: Turns out it was the carbon build-up on the piston crowns that was getting hot and causing the gas to pre-detonate. I'm sure the other things I did along the way helped for the most part (replacing fuel injectors, tps, timing chain, checking all the sensors, etc. see main post). I ended up taking the head off the engine and scraping all the carbon off the piston crowns. I also took the plenum and intake manifold to a machine shop to get thoroughly cleaned. This job was a PITA and I ended up snapping a head bolt, breaking my already replaced timing chain guide, and having to replace exhaust manifold posts). After all this and putting the engine back together...NO MORE PREDETONATION!!!! I was still having an issue with hard warm starts after all this.

Idle Issues / Hard Warm Start: For the last two years I've been having issues where my car would not want to start easily after I had driven it and let it sit for 30 minutes or so. I'd have to blip the throttle and the issue kept getting worse and worse. One day on the freeway my car died on an offramp because it was idling at 100 rpm. I could pretty much rule out IACV because I had already replaced that when I bought the truck 4 years ago. When I checked my freshly adjusted idle screw, it was completely bottomed out. The o-ring was so worn out the idle screw would get sucked to the bottom 5 minutes after I started driving. Replaced the idle screw and my idle returned to somewhat normal (still had warm start issues). After scratching my head for the last year about the warm start (felt like I double checked literally every possible culprit), it turns out that I was having a vapor lock issue. Replaced my aftermarket gas cap with an OEM gas cap and have seem noticeable performance increase and no warm start issues. For something so simple I literally wasted a good chunk of my life diagnosing and thinking about this problem.....

TL;DR
Taking the head off my engine and cleaning all the carbon from the piston crowns and intake fixed my pre-detonation issue. Replacing the o-ring on the idle adjust screw and replacing an aftermarket gas cap with an OEM gas cap fixed my hard warm start issue and gave me much more consistent performance after the car was hot.

 

Congratulations on Fixed!. Just a short anecdote here: I have an '89 22RE 2wd 5 speed. I got t secondhand from my brother. It used to ping real bad in summer here in Fresno. He said it always did it and the mechanics couldn't solve the problem. It was bad enough that I had to run 91 during the warm months, and baby the throttle opening. a few years ago, it started running on three cylinders. Tech found one bad injector. I asked if the "rebuilt" injectors were OK, and he said they'd had no problems with rebuilt. So, had them replace four injectors with rebuilt. After that the pinging/spark knock mostly went away. If I run 87 now, it's still a little bit sensitive to throttle during hot weather, but nothing like before the injectors replacement.

 

So my problems have come back I started running 89 octane and all was good. All of a sudden I started getting pinging and powerloss under load again. I've been re-checking everything and the only thing I can find that is weird is my timing seems to be shifting. I've been checking it after drives and last drive it was 3 degrees jumpered and today it was like 4.5. Unjumpered it was also bouncing around and I remember it used to be pretty steady on 12 degrees.

Things I've rechecked:
TPS mechanically and electrically check out.
TPS readjusted
Idle set screws returned to factory and dash pot adjusted
Fuel pump / regulator checks out.
Readjusted valves (were a little tight)
Started compression test but loaner tool exploded after #1 (174 psi for that cylinder though)
CSI works as it should
Spark plugs look perfect (brown paper bag color)

Things to check:
Vacuum leaks (need to get a tube for my propane tank to check)
New ECU (either junk one or swap with a friend. Anyone live in San Diego??)
Recheck engine grounds from ECU
Knock Sensor (need to check to see if circuit is still intact since I've done a lot of work on the truck)
Compression (maybe my compression is just high??)
Timing Gun (need to verify accuracy with someone elses)
Distributor shaft play (read that it could cause small shifts in timing)
Harmonic balancer (still don't know how one verifies theirs is good)
O2 sensors (previously checked out about 1.5 years ago)
Back pressure from cat (passed smog easily recently so O2 and this are at the bottom of the recheck list)
Recheck various other sensors (ECU temp (practically brand new), etc.)
Swap my new 4.88 diffs in (maybe a stock gear ratio will take some of the uphill stress off the engine and make it less prone to predetonation. Currently running 31's with 4.10s but looking to upgrade to 33's and 4.88)

Open to all other ideas!!!!!