Backfire/Studder under acceleration

[spectre6000]

One man deal. Gauge will stop at it's highest reading so you can get out and look at it. Then you'll have to reset the gauge before you go to the next one.

Depends on the gauge. I had one once that you had to watch. It was old though, maybe wasn't fully functional.

Agreed on the number not mattering in this case. There is a range of compression you should expect for a healthy engine (145 sounds like a good enough number), but in your case you're looking for something with some significant deviation (specifically in #3 from the code).

Keep us posted! We're all rooting for you!

 

[T4RFool]

The Results:

5 - 175 - 6 - 180

3 - 175 - 4 - 175

1 - 175 - 2 - 170

Here are the results of my compression test. I tested twice! just to be sure. Drivers side.... a pain, enough said. Interesting note, the drivers side spark plugs looked a little more fouled than the passenger side, not much but enough for me to take notice.

 

[spectre6000]

These are some talented gremlins!

Kinda puts the kibosh on the valve seat theories... Toyota bottom ends are bullet proof, but the rod theory is still in play...

I'm still stuck on the fuel and spark. You've tested the injectors, but not in a way that leaves no questions. Spark has been tested as I recall you did the spark plug wire trick, though with the coils being on the plugs it might be a little different result than what I'm used to...

I know this is probably getting old, but break down fuel and ignition systems and do a run through of what's been tested and what's been replaced. I.e.

Fuel system
Fuel pump - replaced
MAF - tested
injectors - tested
fuel filter - replaced
...

ignition system
ECU - replaced (used)
spark plugs - replaced
spark plug wires - replaced (1 year ago)
...

etc.

 

[T4RFool]

After the compression test showed little as the culprit my mechanic buddy from out of state urged me to disconnect my cat just to eliminate it as a possibility. Took me a long time since I couldn't get a grinder up in there to cut the bolts, I had to resort to using my dremel, tedious process but it got the job done. unfortunately I haven't been able to get it running since the compression test, I'll give it another try tomorrow, hopefully it'll start.

A curious note of interest, I turned the key to the on position earlier and noticed a high pitched whine coming from the engine bay. I couldn't place the whine to a specific location but it sounded as though it was coming from under or behind the intake manifold. Not sure what to make of it so I thought I would post it up.

 

[T4RFool]

Another Idea:

So I have this idea of what it could be but I don't have much to go on other than the symptoms. Spectre6000, you got me thinking about the fuel system yesterday, back to the most probable causes. Where is the the fuel pressure regulator? I suspect this be the culprit this whole time, but I can't seem to find it. I'll take the manifold off again if I have to just to test it. I suspect this may be the reason why it doesn't start right up again if its been ran, a tear in the diaphragm could cause a flooding condition on the next start up giving it a long crank with the eventual stall or not starting at all.

 

[curtperry]

Where is the the fuel pressure regulator?

The FPR is at the rear of the drivers side fuel rail. A failure of the FPR should be a throttle dependent symptom (because throttle controls vacuum and vacuum controls the FPR) rather than rpm dependent like yours is.

 

[spectre6000]

It may be throttle dependent disguised as RPM dependent... The RPM had to get there somehow.

I hadn't thought fuel pressure regulator because it's not a system I've ever thought about... Carbs are low pressure, and you test the fuel delivery by running the pump into a dixie cup and seeing how long it takes to fill up! Haha!

 

[T4RFool]

Well the cat idea was a bust along with the fuel pressure regulator. It decided to start up this morning, I revved it up a few times to test out the cat idea and that produced no change. So I clamped the exhaust back together until I get bolted back together, obnoxiously loud. I then tried out the FPR idea. I disconnected the vacuum line and ran the motor, trying to observe any fuel leaking out. I ran it for 10-15min before finally giving up and deciding that no matter how much I want it to leak fuel, it wasn't going to.

 

[theizzardking]

Well the cat idea was a bust along with the fuel pressure regulator. It decided to start up this morning, I revved it up a few times to test out the cat idea and that produced no change. So I clamped the exhaust back together until I get bolted back together, obnoxiously loud. I then tried out the FPR idea. I disconnected the vacuum line and ran the motor, trying to observe any fuel leaking out. I ran it for 10-15min before finally giving up and deciding that no matter how much I want it to leak fuel, it wasn't going to.

well that sucks!

 

[T4RFool]

HOLY F***ing S**T

I FIGURED IT OUT!!! After all this time it was in fact a sensor, not a bad sensor though. It turns out that the crank position sensor can cause all of these problems. I never tested the senor though, keep that in mind. Apparently when I took it to the shop to get the timing belt done, they disconnected the sensor but never connected it PROPERLY! They half a**ed plugged it in, it looked plugged in but it wasn't. I got to fiddling around with stuff today, just double checking things. I went and touched, just touched, the plug and it feel right off.... I plugged it back in properly and started it up and boom, revved it right up past 2500, no problems. I couldn't believe it! I reset the ECU, cleared out any codes and just sat there and revved it in disbelief.

I never considered the crank position sensor because I thought that it would effect idle, there should have been a CEL right? It's almost like it was plugged in enough to work sometimes. I don't know what to think now cause I am relieved that I figured it out and don't have to buy anymore stuff but at the same time super pissed that the shop missed that TWICE!!! I have enough spare/replaced parts to keep it running for a long time now but at the same time, I cant go out and drive it because my exhaust it still disconnected. I feel stupid because it was something so trivial, so simple.

 

[AZ4FNER]

Wow, congratulations!!! What a relief it must be. I have to commend you on your diligence to see it through and not give up. Hope your truck repays you with the same kindness, and gives you many troublefree miles.

 

[chris_96runner]

Wow haha, that's awesome man! I had a similar problem with my old '89 240SX, I bought it cheap and couldn't figure out why it wouldn't start. (which was why the previous owner sold it) Turned out it was a sensor not connected properly! Good to hear you figured it out!

 

[theizzardking]

i reiterate this becuase all of that time money and effort and the shop misses a plug that's not in all of the way....

 

[T4RFool]

izzardking, that is exactly how I felt when I figured it out.

Seriously though, you guys have been immensely helpful. I can't even begin to describe how much I appreciate all the input. Every thought and comment was helpful. A huge part of my thinking process is just bouncing ideas around, if not for you guys and this site, I probably would have given up a long time ago. All is not lost either, I may have spent a lot of money on stuff that didn't need fixed but I have now amassed a stock pile of spare parts and learned a lot more about my vehicle. Many maintenance things were found that require attention and were fixed or will be fixed, things that I wouldn't normally have checked or paid attention to.

Lesson learned though, through the aggravation and hopelessness, persistence will pay off.... and check all your sensors no matter what.

 

[spectre6000]

WHAT THE ****???!??!?!!!?!???!?!!??? Send them a ****ing bill! All of the parts, all of the time, all of OUR time, and probably some extra for emotion duress. That's bull****. They owe you BIG time. If they did the timing belt, that and everything associated with it should have been their first stop the first time.

Seriously, I'm glad you found the problem, but this serves to illustrate in spades why I don't even trust shops for such simple maintenance as an oil change. That's just ridiculous. I'm truly glad you got it fixed, and I know you've got to be on cloud nine right now. You have what it takes to truly call yourself a car guy for sticking that through to the end and making it right. I bet you learned a lot. Hell, I learned a lot through this, but you shouldn't have to pay private school level tuition for that sort of experience...

 

[T4RFool]

this serves to illustrate in spades why I don't even trust shops for such simple maintenance as an oil change.

I agree completely but having never done a timing belt on my own and I was without a place to work, garage or cover, I opted to have a shop do it. I wont make that mistake again. I almost NEVER go to a shop unless I absolutely have to. I more often than not I would rather do the research and figure it out. But as I don't have my own garage yet, there are some things I'm not comfortable tearing into just yet.

 

[kball]

To me it sounds like a timing issue, maybe not the belt but a sensor like the crank position sensor. Maybe you're not misfiring but firing at the wrong time. Like when spark plugs get so old they sputter and mis when slowly accelerating under 2K rpms. Also you mentioned it wouldn't start one time after driving it. I've also read about the CPS causing this but it's not common so.. just a thought.

From page 2.

 

[T4RFool]

From page 2.

If your doing an I told you so, just stop. The sensor wasn't bad and the symptoms match up with so many more probable causes, spark plugs, plug wires, coil pack, fuel pump, fuel filter. It wasn't until I found out that all the cylinders were missing equally that I had to consider what might cause that, ECU, igniter, fuel pressure regulator. Another reason to not consider it right away was that there was no code. I'm not saying that's an excuse not to check it but when your CEL code isn't related to the CPS (p1335), your going to check what is related to the code first(p1300). Also, I did take back to the shop and they told me everything checked out. I know I said that I tested the CPS but that was the cam position sensor, not the crank.

P.S That was from page 5

 

[kball]

If your doing an I told you so, just stop. The sensor wasn't bad and the symptoms match up with so many more probable causes, spark plugs, plug wires, coil pack, fuel pump, fuel filter. It wasn't until I found out that all the cylinders were missing equally that I had to consider what might cause that, ECU, igniter, fuel pressure regulator. Another reason to not consider it right away was that there was no code. I'm not saying that's an excuse not to check it but when your CEL code isn't related to the CPS (p1335), your going to check what is related to the code first(p1300). Also, I did take back to the shop and they told me everything checked out. I know I said that I tested the CPS but that was the cam position sensor, not the crank.

P.S That was from page 5

Uh, no, it's not an "I told you so" because none of us knew "so" because we are all here GUESSING to try and help you out!

I was just saying, I guessed right! :trophy:

And for what it's worth, I never agreed with any of the other suggestions about plugs or compression etc...

Show me how compression or coil packs will make an engine run perfect all the time until you consistently hit the same rpm over and over. Oh, and that same consistent rpm just recently dropped from 4k to 2500...? Not going to happen.

 

[T4RFool]

Uh, no, it's not an "I told you so" because none of us knew "so" because we are all here GUESSING to try and help you out!

In that case yes you did win lol

to be fair with the coil packs though, they do fall in line with the p1300. the compression test, not so much but it was an easy test and it ruled out valves. I was surprised that it was the CPS though, it seems odd to me how it could register enough to not throw a code but not enough to cause problems. I still think its a unique case of WTF.