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| This might be a silly fuel pump question....; But it might have nothing to do with the fuel pump | |
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| Tweet Topic Started: Nov 2 2016, 06:43 PM (707 Views) | |
| MarkyMayhem | Nov 2 2016, 06:43 PM Post #1 |
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Hello there forum. 1996 4cyl auto. Lightly rebuilt engine swap. Since the swap I've had an intermittent stumble. No codes. With a scanguage i can see thst the short term fuel trim goes max positive during the stumble - which means an excessive lean condition. I've found that .5oz ATF per gallon of gas eliminates most of the issue. Or did. Now I am still getting the stumble along with (increasing in frequency) an occasional start-die on the engine followed by a normal start-run. The STFT has no reading during startup so.... Injector looks good, good pattern. Haven't been through the FSM low fuel pressure test yet. But - I am strongly disposed towards replacing the fuel pump. in my experience at 255,255 miles or more (where I am) they wear out - so it's not a bad idea to just replace it anyway... Just wondering - any other thoughts as to cause/diagnostic procedure? -M |
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| MarkyMayhem | Nov 2 2016, 06:54 PM Post #2 |
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Ps - in getting my emissions test I checked and replace all vacuum hoses redid the EGR system the EVAP system xcetera |
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| dayle1960 | Nov 3 2016, 06:22 AM Post #3 |
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Fastest Hampster EVER
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Have you thought about a clogged fuel line? 5hat many mile on a fuel system could cause build up and restrictions inside of the fuel lines. |
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| MarkyMayhem | Nov 3 2016, 08:42 AM Post #4 |
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No I haven't really... A fuel line I think would not be intermittant under most all circumstances. They all look fine, I've been in there plenty. Haven't had the tank off though so Ill check those when I drop it. Also - it always seems to start & run fine in closed loop when its dead cold, although if the fuel pumo is going out I expect that'll happen one day. I think the key is the ATF fixes most of the problem. My theory is extra fuel pump lube, maybe some solvent like action... -M |
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| Woodie | Nov 4 2016, 04:41 AM Post #5 |
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Sticky fuel injector is more likely. |
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| MarkyMayhem | Nov 4 2016, 09:43 AM Post #6 |
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I thought about that and while it is still on my list of possibilities it's got a good spray pattern and the intermittent nature of the issue just seems to be more likely to be something else. Plus there's no really good way to test the injector so it would just be a matter of throwing one in there. I'm trying to avoid throwing Parts at it but I did get a fuel pump for $9.... Also in my experience with throttle body ininjectors and metros the fuel injector will definitely give you trouble in closed-loop dead cold start mode if it's really failing badly. Edited by MarkyMayhem, Nov 4 2016, 09:45 AM.
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| freegeo | Nov 4 2016, 09:58 AM Post #7 |
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What was your max number on the STFT? What are your STFT and LTFT #'s at idle?
When the engine is first started and the engine is in open loop the STFT will be 0. The STFT is only active while the engine is in closed loop. |
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| MarkyMayhem | Nov 4 2016, 10:21 AM Post #8 |
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I know stft is 0 in open loop. Think I mentioned it - thats why my start #s are non existant when i get the occasional start-die, then start-run. However - normally LTFT is around -10 and stft runs between -7 and 1.8. Lately LTFT is more like -2.8 to 0 and stft runs from -4 to 20, but when its running ok its around -7 to 10 or so with a lot of jumping around 1.2 to 10 or so. On my stumble it goes 0 to 7 to 13.46 to 16.8 to 20 stumbles bad I feather the gas pedal & it usually settles out back around 0 to 3.6 At idle right now, LTFT is -10.2 [normal for this car] and stft is between -2.8 and .78 When its about to do its bad thing idle ltft is more like 0 and stft varies from -1 to about 10 avg probably 3ish followed by stft jump quickly to max -20 Edited by MarkyMayhem, Nov 4 2016, 10:27 AM.
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| MarkyMayhem | Nov 7 2016, 08:26 PM Post #9 |
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My $9 fuel pump came in. Im pretty sure I have an extra known good injector - if not one of my old cars is at a local scrap yard with a replacement injector and hex head 4mm bolts, so I may grab that just because. Anyway I'm going to do the tank & pump this week. If that doesn't fix things, Im only out a few bucks, and I can always bust out a solder gun to loosen the locktite and try the injector replacement. I just LOATHE throwing parts in the general direction of the problem, but I can't think of any pertinent tests to try short of rigging up a fuel pressure gauge I can read while driving, and waiting until I can read it during the stumble & especially a start-die situation. Any suggestions before I tackle this *€:!=%? -M Edited by MarkyMayhem, Nov 7 2016, 08:27 PM.
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| MarkyMayhem | Nov 11 2016, 06:15 PM Post #10 |
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New fuel pump installed so far so good. Drivability had gotten down to ridiculous levels before today. I best offer down a new injector on eBay for $17 and got my screws loose so I will probably replace that as well but it looks as if the fuel pump was the problem |
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| Richard123vmt | Nov 11 2016, 11:42 PM Post #11 |
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You are making too much out of replacing an injector. The only secret is to not even bother with a screwdriver to get them loose, but go directly to vice grips which will grab the head to get it loose (and tight again). Then the screwdriver to actually take it out. To put in the replacement it can only go one way but you should connect it first to the connector and then fit it in. Be sure it is seated before you tighten the screws. There are some O-rings but they seldom give trouble. |
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| ptcapboy | Nov 12 2016, 06:41 AM Post #12 |
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I think extra caution trying to get those damn screws out is time well spent (like heating them with a soldering gun) he doesn't want to be like me and snap off both heads and pay 700 bucks for a tow and a rip-off repair job- |
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| sphenicie | Nov 12 2016, 07:31 AM Post #13 |
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$700 WTF...........Get your McGiver on man! you could have taken a taxi 100 miles, bought the entire TB, taxi back to car for less than that! next time you have a pocket full of cash that you want to give away, just call me! |
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| MarkyMayhem | Nov 12 2016, 07:40 AM Post #14 |
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DING DING DING! I broke off an injector cap screw once. Fixed it myself. Sucked. And the junktyarda are getting more and more bare of spares. BTW - I did crack the locktite. Warm engine, the right screwdriver, and luck - they cracked right open. I doubt I even need bolts. Which I think, for future searches - injector bolt screw M5x.8. I got 16mm which may be a bit long. 14mm would be right on Edited by MarkyMayhem, Nov 12 2016, 08:37 AM.
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| MarkyMayhem | Nov 12 2016, 07:47 AM Post #15 |
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Also for future reference if you snap off the screw that holds the injector in get the other screw off however you can even if you snap its head off as well. If the first screw didn't break off flush with the metal under the injector cap that is. Then you can remove the throttle body remove the plastic injector cap heat the screw with some gas that would be the broken piece and use Vice grips on the stub |
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