Engine missing

G

ggf

Registered
Hello everyone,
I realize that I haven't been around for a while. Well interests change and I just don't have the free time I used to. Anyway, I'm hoping I can ask for some help. I just recently sold my 97 Mark VIII LSC after many many years of outstanding service. (has about 185K on it) Unfortunately, I sold it to my brother and no he is having problems. (of course) The engine is missing, at idle, at revs, seems all the time. CE light indicated lean condition. He had his small town mechanic check fuel pressure, which was low, and change the fuel pump for mucho $$$. Pressure is back up, but engine is still missing. They cleaned the injectors, then, well, gave up. Couldn't figure it out. My brother went through cylinder by cylinder with a new coil and it appears that didn't solve the problem. (what is the fuel "injector trick" I've read about to find out which coil is bad, anyway. I usually have to go through each one with a new coil until it stopped missing) Any suggestions as to what to try next? The fuel filter has about 30-40K on it and the mechanic indicates that the pressure is within spec. Its got to be an ignition problem. Oh, and the car seeps oil out of the valve covers into the plug holes, but we cleaned that all up, though at least one boot looks "bloated". (this has been going on for several years, I just clean them out once or twice and year with no problems) I could sure use the help, I think my brother is about to kill me ;-)
Thanks
 
With 30k to 40k i would have changed the fuel filter, also when was the last time you chaged the O2 sensors?
 
dumb question but did you change your plugs? If you just did change them maybe you kinked it and it has no gap now.

oh and you need a new gasket for your valve cover if you have oil in your spark plug holes. The circular gaskets for each cylinder come with the valve covers.
 
steve said:
With 30k to 40k i would have changed the fuel filter, also when was the last time you chaged the O2 sensors?
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Ok, fuel filter should be on the list of things to do. I know its realitively cheap and easy to do. Plugs are motorcraft platinums with probably 50K on them. They looked fine when we inspected them, but maybe they could be changed as well? As far as the O2 sensors go. Never changed them, at least not since 80K. Are they easy to do?
 
ggf said:
Ok, fuel filter should be on the list of things to do. I know its realitively cheap and easy to do. Plugs are motorcraft platinums with probably 50K on them. They looked fine when we inspected them, but maybe they could be changed as well? As far as the O2 sensors go. Never changed them, at least not since 80K. Are they easy to do?
Click to expand...


I would at least change the front two O2s if they have more then 100k miles on them. They can be a bit hard to get out, like most work if you have a lift the work is easier.
 
Yep, got the tool to change the fuel filter. Looks like we'll be changing some coils, plugs and fuel filter at first. Then the O2 censors if that doesn't do it. Maybe we'll change them anyway. From what has been said they are overdue. But wouldn't a bad O2 censor trip a code? It does on my cheapy Saturn.
 
Woah, guys. Let's take this back a step. You're talking about throwing parts at a car, some of which can be expensive and I don't think you're going to get very far.

You say your fuel pressure is good, but you're running lean. That is NOT an indication of ignition failure or fuel filter failure. Your O2 sensor is telling your PCM that there is an abundance of O2 in your exhaust. To combat this, your PCM is SUPPOSED to add more fuel so it can burn more O2. Somehow, it's not. Your ignition system is NOT a load-determining component and WILL NOT create a lean condition. It may SEEM this way because a failed ignition would result in failing to burn the O2, but if that were the case, your knock sensors would activate and you'd probably end up with a number of codes, namely an engine misfire code among others.

The fuel filter is good because if it weren't, your fuel pressure would be low and changing the pump wouldn't have done anything.

So... What now? Well, if you're running lean, you need to look at your load-determining sensors. These would be your TPS, your O2, and your MAF. Usually when an O2 sensor fails, the PCM will go into an open-loop mode and the majority of what you'll see is a check engine light and that's about it. When a TPS fails, it can create a similar condition to this, but MAFs are much more likely to fail before a TPS simply because of their construction as well as being exposed to the elements in your air intake.

But what about when the car is normally in open loop? The Mark VIIIs run for about 30 or so seconds before entering closed loop (it's based on time, not on heating the sensor like on other vehicles). When your car is in closed-loop, it uses O2 sensor input. When it's in open-loop mode, it uses ECT, TPS, MAF, and other sensors to determine what air/fuel ratio it should be using.

So basically what I'm saying here is... Does it act up in open loop too? Or does it only start after about 30+ seconds of running? If it does, that could be your O2 sensor right there, but this isn't a very scientific test and can be relatively inconclusive if you don't notice any difference between open and closed loop.

The best way to go about doing this is to cross-reference your MAF readings with your TPS readings under a snap-throttle test. Assuming you don't have a scan tool or digital oscilloscope at your disposal, this may be a little difficult.

Nevertheless, your MAF sensor is given top priority for fuel enrichment and enleanment. Have you cleaned your MAF recently? Did you use any kind of solvent that WASN'T MAF cleaner? If so, you could've potentially damaged the sensor.

If you haven't cleaned the MAF, I certainly would give it a try. Your car has 185,000 on the clock, right? That's a high mileage vehicle with a good potential for dirt to have lined up in your intake. It wouldn't surprise me if your MAF was just a little dirty. It may not work, because sometimes MAFs are just too far gone and can't be salvaged with just a little spray. But hey, for $5-$10 for a can of CRC MAF cleaner, it couldn't hurt, right?

If you want my opinion, you should spray your MAF down before investing hundreds into replacing sensors that may not need to be replaced. Remember, throwing parts at a car is NOT the way to fix it.

EDIT: What about your air filter? Is it clean? If not, it could've helped in dirtying up your MAF sensor.
 
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The car was running lean before the fuel pump was replaced. Since then, there have been no codes thrown. As far as the open vs. closed loop question, I'll have to ask my brother if he sees a difference. At this point he has purchased 3 additional coils. There are only 3 original coils left in the car and I'm thinking he will try to change those and see what happens. The boots on the coils are all pretty good condition, aside from one. But that should have been addressed when he went through one by one to find out if there was a single defective one. Last I spoke to him he says it appears to miss all the time, until he is up to speed. I suppose, when it is under any sort of load. The air filter was kinda dirty, but it is a K&N, so I didn't think that would be an issue. He will be cleaning it in short order. I will discuss with him the MAF cleaning as suggested. Thanks for the input to this point.
 
+1 for what steve says!

ggf, it doesn't matter if it doesn't throw codes. Codes are just parameters set by the computer, and can't necessarily diagnose whether a sensor is functional or not. A perfect example would be my 1996 Saturn SL-1. GM uses a MAP sensor in place of a MAF, but it had the same symptoms you describe while showing absolutely no codes at all. The MAP was shot.

You'd be surprised how often MAPs and MAFs are the root problem of issues like these.

Good luck and let us know.
 
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