OK, this is a serious dumb assed question, since I am grasping straws here, on my '72 with '89 roller engine in it for some time now...
iron heads, forged pistons, around 9.5 comp ratio and DPFI, TPI style with ZZ9 cam.....

so the question is as I recall, I adjusted the valves with cold engine, and so everything has been fine for some time now, EXCEPT when in hot weather the engine warms up totally, NOW on these 80f+ days it's running fine TEMP wise, but runs like crap....I have been all through this damn dawg, and am thinking computer screw ups...but....the thought hit me, when engine is cold and/or in cold weather for Florida that is....40-60f outdoors, car runs fine.....70f++ it has more misses than a HS Prom....so....

I have been adjusting hydraulic valves for decades untill snug...is there a possiblility the engine heating up causes a valve to stay open causing a misfire?? can this happen?? I adjust untill snug on the pushrods, and no further....

any clues ??anyone/??


I have been all through sensors, no codes set, the 1227730 computer has been replaced many times, wiring checked, thing been petted over so many times it's a joke, the cyberdyme a/fuel gauge hooked to the O2 sensor says it goes lean as hell, and so does my voltmeter, runs fine cold, but when goes closed loop at about 160f or so, the O2 starts leaning it out to .1 volt or maybe less on tip in, the idle is messed up badly, and so I have lots of misses running down the road, it's embarassing it runs so badly....

I realize I"m grasping at straws on that valve adjustment, but I"m getting desperate, so do the valve adjustments tend to tighten lash when hot??

GENE

 

A few things I'd do. First I'd pull the ignition module and have it tested, I've had Autozone check mine, just make sure they run it through 10 cycles. Second, did you disconnect your ESC wire when you set your timing? Do you have headers on it? Then I'd be inclined to check my fuel pressure. And lastly-for now, I'm not a big fan of adjusting my valves cold and calling it good, On my cars I go back and readjust when warm, I like to be able to twist the push rod freely, while making sure I don't have any up and down play.Good luck

 

Mine runs like crap when it gets hot too. I'm gonna check the ignition module...

 

I hope your adding at least a half turn after this point

 

Regardless, the rocker adjustment is not his problem. The original poster was questioning whether or not the rockers were too tight, and when hot were tight enough to hang a valve open. Setting the rockers at zero lash won't hang a valve open, hot or cold.

1/2 turn past zero lash is the most popular adjustment, but it is not correct for all applications. Comp cams R lifters are a hydraulic lifter that calls for a zero lash adjustment, for example. We don't have enough information about his valve train to say for certain that he should be tightening the rockers to 1/2 turn past zero lash.

Like I said though, not tightening the rockers enough will not cause a valve to hang open, which is what the original poster was questioning.

 

If you are able to send me a datalog I could look it over in my free time and try to find anything that sticks out to me as a possible cause. My first guess would be a bad O2

 

Alvin, I have a scanner tool that covers my car , and have not noted anything except some meaningless codes on the scanner, but never have my SES light come on, stupid thing is, couple hours ago I changed the ignition module, with the vague recollection of doing that couple of years ago, and so it SEEMS to have quit doing that stumble...I need wait to later in PM for heat on roads to build up, and take another test drive....figgers it's cooler today....

I have a sneaking suspicion I need relocate that ignition module from dist base where NO ELECTRONICS like that heat spot, designed or not, and put it on a heat sink (dist base would ADD heat to it), and stick it inside the car.....I"M an old geek, so wiring is not an issue....
the sending coil is fresh, and I have been all over this, so is the spark coil in the cap, I just reinspected it today, looks brand new still....

I have subbed MAP, and all temp sensors from time to time, even tried hanging a water temp sensor outside in the air under the hood, behind fan....THAT was an obvious no go....

OH, I bought a new O2 sensor yesterday, no go....no change what so ever....

I don't think I can log data on this scanner tool I have, I know I don't have a printer or a portable PC, much less software....

GENE

GENE

 

I was not saying it was associated to his lean condition, it just caught my eye as i have never used a hydraulic lifter that had no preload.

 

The first thing I would check are the fuel injectors. Frequently when hot, the coils will short. When cold Disconnect each harness plug and measure the resistance between the two fuel injector terminals, for each injector. Do the same thing with the engine fully hot. If you get a lower resistance reading on any of them when hot, then you found your problem.

89-91 is when GM went away from the Bosch Injectors and went with the garbage Rochester injectors. This is a very typical failure on 89-91 TPI cars.

 

I agree,thats a great place to start...but Im unsure what injectors you have..use a voltmeter and check the ohms cold and hot...let us know your findings...also are you running an egr valve?

 

Right now, they are Ford 24# injectors, I have had 22# in there also at one time last year, went back to the 24# last summer, trying to get rid of this stumble....

Any one have any experiences with Breathless Performance chips?? Ernie there used to be a sponsor, but I don't see them/him listed anymore, talked to him couple years ago about this and he wanted another 200 bux to look at it again....been about 6? years since I bought it....it was before I met my wife yet, and we married 5 years now...shows how much/long/many times I have fought this issue but there are only so many hours in a day and in cooler weather it's not an issue...

GENE

 

Judging from what you said about being good in open loop and in general, I would say you need to look at the tune on the chip. What does the INT, and BL show, sounds like it is beyond what the computer can comp. I also think you should take up Alvin on his offer.

 

about the ignition module, that's why when they test them they run them through at least 10 cycles-getting them hot enough to see if their failing.Good luck.

 

Well, I did change the Ign MOdule yesterday did notice an improvement, bout wouldn't I know, i'ts only about 70f this morning the thing ran fine up and down the road, even when sitting at lights, the fan comes on, and it drove damn near normal....still coolish on the air, and lo humidity....need this weather to come around outta the south again to get the temp/humidity up there to prove anything though....

history has been for over 6 years now, every time i think it got it whipped, damn if that stumble don't come back again....

GENE