INTERMITTANT "Missing" and rough running/idle
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HT4100 4.1, 4.5, 4.9 Discussion, INTERMITTANT "Missing" and rough running/idle in Cadillac Engine Technical Discussion; 93 Eldo base 4.9l (non-northstar). 86k miles. Car seems to be missing a cylinder sometimes (most of the time) but ...
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    JeremyG is offline Cadillac Owners Member
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    INTERMITTANT "Missing" and rough running/idle

    93 Eldo base 4.9l (non-northstar). 86k miles.

    Car seems to be missing a cylinder sometimes (most of the time) but periodically it's fine. Last night I drove it 75 miles and after about 10 miles at constant RPM it started running great. Then it ran like a top for another 15 miles of city driving. Shut it off, turned it back on and it was back to running bad.

    I have no codes that relate to the engine (onen I039 current code). The rest of the codes are "history"...

    Of note:
    P047 IPC-PCM Data Problem (history)
    P030 ISC RPM Out of Range (history)


    So where do I start my troubleshooting? It just seems to me to be either electrical (ignition) or fuel (injector) since if something BAAD (dead cylinder or something) was wrong, it would be constant, and never run right.

    But more thinking... and wouldn't a bad injector throw a code? Would a bad plug wire throw a code?

    I was thinking for the cost and ease of job to just replace the plug wires, they probably need replacing anyway... so if that doesn't work... what's next?


    Isn't there a way to disable spark or fuel to a certain cylinder in diagnostics to see if the RPMs are effected and to see which cylinder is acting up?

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    STS 310's Avatar
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    Re: INTERMITTANT "Missing" and rough running/idle

    Fuel pump possibly. Can you check the pressure yourself? Im not familiar with the 4.9, so i dont know where the rail is or the check valve.

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    JeremyG is offline Cadillac Owners Member
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    Re: INTERMITTANT "Missing" and rough running/idle

    Hmm... I could probably test it myself as I do have a tester that I mistakenly bought in an eBay auction (thought it was something else). I'd have to find the check valve, though... probably not hard to find?

    I wonder, however, if that would cause what does sound/feel like just one cylinder going out? Seems like that would effect one bank or even both banks?

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    JeremyG is offline Cadillac Owners Member
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    Re: INTERMITTANT "Missing" and rough running/idle

    An update... it's now happening more like 50% of the time and when the engine is missing, it sounds like the car is falling apart. Really rattling the drivetrain, etc.

    Also it seems to run better at 40% or more throttle (acelleration), and worse at cruise.

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    JeremyG is offline Cadillac Owners Member
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    Re: INTERMITTANT "Missing" and rough running/idle

    Ok was just able to do the injector disable and Cylinder #3 is somehow dead.

    I pulled the wire off of the coil and there IS a spark coming off the coil (damn thing bit me again as I put it back on!). So that would mean either bad wire or bad plug or bad injector... or heaven forbid something really bad with the combustion chamber/piston but I can't see any way it could be anything other than wire/plug/injector.

    So tomorrow I buy new wires and replace them all. Let's hope that works cuz I really don't feel like doing a spark plug change on this thing, it looks to be almost as much of a PITA as my Stealth (and I have to take off the entire upper intake plenum to get to the rears on that).

    Any other advice?!?!

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    Re: INTERMITTANT "Missing" and rough running/idle

    i hate to tell you this, but i am almost positive that you have a bad injector. it is not uncommon for the stock 4.9 injectors to go bad. if acceleration is better in high rmp range, that suggests that it is getting some fuel due to pressure. low rpm range is where you will notice the big difference. take your plugs out and inspect them. make sure they have correct gap (.060) and are not damaged, fouled, or corroded with carbon and whatnot. to check the wire, take a timing light to the wire with the car running and look for light on the gun. if it is not firing, you have a bad wire. to check the injector, try and get a screwdriver on top of it and see if it is clicking. a stephoscope can help even better. if the injector is not clicking, it needs replaced.

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    JeremyG is offline Cadillac Owners Member
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    Re: INTERMITTANT "Missing" and rough running/idle

    Ok, cool. I guess no big deal if it's an injector, at least I'll know it's not something horrible.

    I think I'll still replace the wires, car has 86k on them, it's nearly due anyway and for $50 or less and an hour of work, might as well.

    I will also take out at least the front 4 plugs to inspect, not looking forward to doing the rears, but probably will get crazy and do them, too. If I take them out I'm going to replace them, again for the cost if the old ones are already out, I'm just gonna do it. From what I've read, I should just replace with the stock ones, right? I don't plan on modding the car for more power but I do want them to last and the car to run as good if not better than stock.

    So, let's say it is an injector.... what's the next step? Should I just try to buy a used one from a used parts yard (junkyard) or should I replace all 8 or what? Half of me says just replace all 8 but of course I haven't priced them out yet. Any suggeston on the most reasonable priced retailer for OEM or OEM style injectors (new)?

    BTW I built my stealth to 500+ hp with turbo replacement, injector replacement (twice LOL), etc. so I'm decent with a wrench... just admittedly a bit sick of working on cars (the Stealth breaks a lot )...

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    Re: INTERMITTANT "Missing" and rough running/idle

    check out ebay for good used injectors. some of the folks here seem to have good luck with them. new replacement injectors will run about $80.00 per injector. FYI, the stock injectors will be 18 lbs/hr...i think.

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    Re: INTERMITTANT "Missing" and rough running/idle

    I replaced my injectors a few months ago. I bought them new and I think they were $45 - 50 ea. I don't remember the name of the company, but it was something like "Midwest injector" in Illinois near Chicago. They have a web site.

    After I replaced all, the car started quicker and ran with less "pings". Also, when I pressed the throttle while the car was still, the engine response got much better.

    But I have another trouble on my engine right now, it is not running well...

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    JeremyG is offline Cadillac Owners Member
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    Re: INTERMITTANT "Missing" and rough running/idle

    Well it's getting worse, now I think 2 cylinders are out so it's time to replace them all...

    I ordered a set of 8 from Linder Technical Services, they should be here tomorrow. $250 for the set, Lifetime warranty.

    Hopefully an injector replacement job is reasonably Do-It-Yourself. I've done injectors 3 times on my Stealth so I have a GENERAL idea of what/how to do it.

    I'll be doing spark plugs/wires at the same time, and also replacing the serpentine belt for good measure.

    I'm hoping this takes care of the rough running. Once that's taken care of I get to do some other minor fixes... like fixing some exhaust leaks and replacing something in the front left suspension (assuming a tierod end or something as there's a clunk).

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    Re: INTERMITTANT "Missing" and rough running/idle

    Quote Originally Posted by illumina
    check out ebay for good used injectors. some of the folks here seem to have good luck with them. new replacement injectors will run about $80.00 per injector. FYI, the stock injectors will be 18 lbs/hr...i think.
    Check out http://www.fiveomotorsport.com/Injector_SetsFORD.asp. I bought a set of injectors less than 1000 miles for $165, with a lifetime warranty. They work fine.

    Ohm out the injectors. Mine were 12-16 ohms for good ones, and under 10 and dropping over time with bad ones. By the time I checked them and then pulled them they were down to less than 2 ohms. The injector driver won't fine at all at that point, it will override and bypass that cyl. I pulled the ECM to ohm them at the wiring harness. (DISCONNECT THE AIRBAG getting in there!!!) Remember if you do it that way, they are positive comon. Meaning one side of the injector is connected to +12V, and the ECM grounds it to activate it. Don't ask why, that is how all of them work. Just design. Easier with high speed switching transistors/FETs.

    I had 3 fail in a very short time. replaced 2 with parts store ones and cost my dad $200, bought the rest for $165 for 8. Can't beat that with a stick!

    Ford, Chevy, V6, V8, almost all use interchagnble injectors. Get 19lb/hr injectors, they work fine and don't disturb emissions. 23lb 350 Chevy ones might at WOT and hurt power.

    Tom

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    Re: INTERMITTANT "Missing" and rough running/idle

    I should have known those places! I thought I got a good deal for those injectors, but maybe not...

    Anyway, I am not sure how your engine is arranged, but I assume it is similar to my engine in the 95 Sedan DeVille. Replacing injectors is very easy. Could be done within 2 hrs (taking it a part and put it in).

    In my case, I have to move the steering pump and reservoir a bit for the part of the fuel rail (the end of the rail that goes to #1 and #3) to get out. And I don't need to touch the large torx located between the fuel inlet and outlet of the fuel rail. That torx isn't holding the rail to the engine, it just put the rail together. Also, I believe the rail should be removed without taking it a part, so basically the fuel rail with the injectors would come out as a whole once you take six of 10 mm bolts (4 holding the rail, 1 for the fuel pressure regulator, 1 holding the throttle cable).

    Before lifting that whole up, I have to take the thick vacuum hose to the brake, coolant hose from the thermostat housing, and the holder that has the EGR solenoid and pressure sensor away.

    Good luck.

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    Re: INTERMITTANT "Missing" and rough running/idle

    Best advice:

    DO NOT ATTEMPT TO BEND THE RAILS!!!!

    The Cadillac dealer my dad was at had 2 rails in the parts bin waiting for people to come purchase them because they tried to pry it up and cracked the rails (fuel leak, nasty....).

    In my case, I bent the mounting tab going down and that has caused me some headaches too.

    You can separate the front and back rails to make it easier. The rear rail can replace all the injectors without removing it completely, I pulled enough to tilt it up on the end by the tstat housing. Made it a little easier.

    Tom

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    JeremyG is offline Cadillac Owners Member
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    Re: INTERMITTANT "Missing" and rough running/idle

    Thanks for the hints guys... here's what I have done so far and I'm done for the night cuz I don't have enough light:

    1. Removed the plastic cover in the front. Removed the air intake, undid a couple vacuum hoses.

    2. Moved the PS pump off to the side, that required me to take off what I think is the tensioner pully from the serpentine belt so I could get to the big long bolt that held the back end of the PS pump on. I was a bit nervous pulling up and sideways on the PS pump since there's a hard line coming down out of the bottom but it didnt' break

    3. Removed 3 10mm bolts (2 on the front rail and one on the regulator). Looking for the others but it's too dark now.

    4. Unhooked the 2 pressure fittings on the rear rail (fuel feed and return lines I assume). Took a 5/8's wrench on the moveable nut and I think a 16mm on the other side to hold it steady.


    It appears that the front and rear rails are loose but won't pull up and out.. I'll have to take a better look at what's holding them down but I assume it's more 10mm bolts.

    It does look like I'll be able to swap the injectors fairly quickly once the rails are pulled up.

    I'm only about 1/2 hour into it, I am estimating 2 hours total by the time it's put back together and I bet I could do it a 2nd time in 1.2 to 1.5 hours at most. I spent a lot of time just looking and figuring things out.

    Any other suggestions or hints??

  16. #15
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    Re: INTERMITTANT "Missing" and rough running/idle

    Good job!

    I think you need to remove 2 more 10 mm bolts holding the rear fuel rail. After that I think you should be able to life the entire rail. Oh, I forgot to say that you have to unplug the connector for the injectors.

    I am not sure if this is recommended or not, but I put a little bit of clean oil between the injectors and the intake manifold, then it became much much easier to pull the rail out.

    Don't lose clips holding injectors to the rail and pins holding the connector to the injector.

    >N0DIH

    Nice advice. When you put the rail back on the engine, would you put the front and rear rails together before putting them on the engine, or after putting the front and rear on the engine?? To me, it was impossible to put them back together after installing them separately (two pipes with O-rings never get inserted all the way)...

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