Timing and Fuel issues...

[heedicus]

So I am still trying to figure out why I am getting 4 point piston failure. The engine just got rebuilt a second time and when driving the rig under a load it had 4 point piston failure in two of the pistons, but I didnt drive it as long.
We have since pulled the engine thinking the mashinist had not bored it out to the proper tolerance. After taking apart the engine again we discovered that it was within toyotas tolerance. The pistons he used were also recommened by the toyota dealership. we are a bit baffled, the thinking now is that the fuel or the timing is causing the engine to run too lean and that is what is causing this issue. The first time we had the engine fail, we replaced the Mass airflow sensor. and had the fuel injection rebuilt. we are currently testing the fuel injection system to see if that could have been the problem.
My question is, is there a computer related issue that could be advancing the timing when it is under a load?
is there a way of testing the computer system or has anyone ever heard of this before?
Any input would be helpful.
thanks,
tren

 

[SUMOTOY]

So I am still trying to figure out why I am getting 4 point piston failure. The engine just got rebuilt a second time and when driving the rig under a load it had 4 point piston failure in two of the pistons, but I didnt drive it as long.
We have since pulled the engine thinking the mashinist had not bored it out to the proper tolerance. After taking apart the engine again we discovered that it was within toyotas tolerance. The pistons he used were also recommened by the toyota dealership. we are a bit baffled, the thinking now is that the fuel or the timing is causing the engine to run too lean and that is what is causing this issue. The first time we had the engine fail, we replaced the Mass airflow sensor. and had the fuel injection rebuilt. we are currently testing the fuel injection system to see if that could have been the problem.
My question is, is there a computer related issue that could be advancing the timing when it is under a load?
is there a way of testing the computer system or has anyone ever heard of this before?
Any input would be helpful.
thanks,
tren

Tren, remember to summarize your other posts and app, tho in doing so, you appear to be speaking to your 91. The FSM should have all the test procedures here. I presume you got proper timing? Did you ck for proper timing advance under load? Fuel pump output test pass (x cc/1min)? Fuel pressure tests (guage on fuel rail))? Static Top Dead Center? As a rule IME, those early Bosch systems are bulletproof, they either work, or they specifically don't, as in the truck won't start. Otherwise, you are most likely back to the basics of fuel and spark. The internals of the engine are most likely failng as a result, not the cause of your problem.

In my audi shop, I see a lot of early Bosch systems, cuz the dealers don't like them (no computer to plug and play diagnostics). This usually necessitates the actual FSM for the truck (not alldata or generic books). I have the FSM for my 94, and Mr. T. gives a LOT of diagnostic trees to follow in this type of testing.

Fuel side: See above +
air leaks
vacuum leaks
PCV system
block in fuel pump pickup
leak in fuel pump line to engine
leak in intake manifold gasket
crack in head

Spark side:
coil output
distributor shaft radial play
rotor and rotor mount
Distributor advance
Faulty-intermittent rpm/TDC reference sender
bad or incorrect plugs
bad ECU ground
triple ck spark plug wire routing/seq
Bad ignition switch
bad wire, connection, connector

Tren, if the truck starts and runs, you have the good and the bad. The good is it runs, the bad is, it runs. Now you are just in the crime scene, plotting away till you find which signal, voltage, or fuel issue is causing the knock. All else fails, a gentle trip on the dyno with the A/F hookup can help emmensely

It's not fun for customers, because it's just time in, all billable hours. But pinging motors (I presume this to be a normally aspirated truck) will cause a failure if the problem isn't corrected. I really doubt the failure should be the focus here. And I also doubt it's the FTU.

HTH

Scott Justusson
QSHIPQ Performance Tuning
FZJ80 supercharged

 

[CJF]

I really doubt the failure should be the focus here.

I'm with Scott on this.

Tren, are you saying the engine was just pinging away and you never did anything about it until the engine failed?? Or...?

Curtis

 

[heedicus]

the engine runs well with no pinging after it was rebuilt and in the vehicle. I drove it for about 30 miles and as I went up an incline the pinging began. I beleive we determined the pinging was from the piston failure. the tolerance on the old engine before it was rebilt was 4 hundreths of an inch past tolerance. So the theory is that I was having a timing or fuel issue on the old engine and was never pinging because the was so much room in the piston. I am trying to determine ways to diagnose the problem before I put the vehicle under a load and have to put in new pistons again. Thanks for all the info I shall go from there.
Thanks,
tren

 

[CJF]

I beleive we determined the pinging was from the piston failure.

Don't want to speak for Scott, but I believe what we're both saying is that it's much more likely to be the other way around.

 

[SUMOTOY]

the engine runs well with no pinging after it was rebuilt and in the vehicle. I drove it for about 30 miles and as I went up an incline the pinging began. I beleive we determined the pinging was from the piston failure. the tolerance on the old engine before it was rebilt was 4 hundreths of an inch past tolerance. So the theory is that I was having a timing or fuel issue on the old engine and was never pinging because the was so much room in the piston. I am trying to determine ways to diagnose the problem before I put the vehicle under a load and have to put in new pistons again. Thanks for all the info I shall go from there.
Thanks,
tren

More information always helps . I'd be chasing fuel or air leak based on the above. I'm not sure I agree with the diagnostic of piston failure causing pinging, I think it's the other way around. Not sure what tolerance you are speaking of, but a piston out of tolerance can make noise, leak oil, but other symptoms are present with pinging, like a big black cloud behind the truck. If it's just pinging up a hill, that sounds like a fuel problem under load (not enough), or an ignition problem (too much) under load. I suspect the former.

I'd do the fuel pump output test and the fuel pressure regulator tests first, then move on down the diag tree. Do you have the FSM? Did you triple check vacuum hose routing to make sure you have everything exactly as it should be?

2 sets of pistons in a bulletproof motor sounds like you are chasing the result of the problem.

IMFDHO (in my free diagnostic humble opinion)

SJ