miss/injectors?
 

ok, I read the "missing" post and it got me thinking. I have a what seems to be a miss at around 1800 rpm's only when I am lightly pushing the accelerator.
I thought it was a sticking injector but now I am going to clean my MAF (Pro-m bullet) and see if it clears up the problem.
If it isn't the MAF, then I think I have isolated the injectors as the problem. (plugs and wires are good) I am running 24's for plugs because of the nitrous FYI
It doesn't miss at idle so how can I check them? I have never messed with them so don't assume I know how to run a test on em! lol

thanks
ed

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My Mustang
91 LX Conv. 52,000 orig mi. Hurst shifter,King Cobra clutch, 3.55 grs, NOS 150 kit, MSD 6al, MSD timing control, malory coil, pullies, adj fuel reg, BBK 70mm tb, Pro-m 75mm maf, battery in trunk, JBA: shorties,subs,strut tower brc, Comp eng. 6 point cage, dynomax 2 1/2" exhaust, Hotchkis lower cntrl arms, MAC cold air kit, off road h pipe.

Ed, scroll down and read my first reply to "Surging Problem - Help" by Lawless, and try checking the TPS that way first. If that checks out okay, try and see if any codes are present. have you pulled and inspected your plugs lately? Any stand out? Have you checked your fuel pressure under the same condition?

Take care
~Chris

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Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

tps is .99, no codes, checked the plugs, they all are good. I havent however checked fuel pressure

You didn't go read it, did you? I'm not concerned with the voltage at the TPS, although yours is dangerously close to 1 volt, which is where the ECM determines whether or not you are at idle. .95VDC is really much better. There is no noticable performance increase between .95 and .99, but .99 is alot more risky, but that's up to you. I want you to disconnect the TPS from the harness, and hook up the leads from a DMM (with a bargraph) across the VREF and TP Sig (grn & orange) wires from the TPS, not the harness). Set the DMM at ohms, and watch the bar graph as you turn the throttle. There's a good chance that you will find a flat spot, where the bar momentarily stops progressing, or even back steps. I've had that happen before. When I tested it for a smooth voltage increase, it wasn't as evident as it was testing it for resistance. My bar graph jumped significantly in both directions while I slowly rotated my throttle. I replaced the old TPS (only had 60k on it!), and the problem was solved.

I'm not saying for certian that's your problem, but your description sounds similar to what my experience was when this happened to me.

As far as checking your injectors goes, try and duplicate the miss in your garage. Then, one at a time, disconnect an injector until you find one that doesn't make as big a difference. Then inspect that injectors harness, and if you don't find something wrong, pull that injector and another one, and swap them. Now try and see if the problem cylinder moved with the suspected injector. If it did, you've found your problem. If it remains in that first cylinder, then there is a problem with the circuit. You should also measure the resistance of all your injectors.

Or, find a shop with a MotorVac, and have them professionally cleaned.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

nope, didn't read it, but I am going to do the steps you mentioned.

I have noticed that the problem goes away after time (since last time I used the nitrous at the track) I dont have the "miss" now but I experience it after running the 150 shot.

for some reason I think its an injector that cant handle the pressure...

Yeah, that little tidbit would have me thinking it's cylinder specific too. next time it happens, pull your plugs as soon as possible. That should tell you which cylinder it is. you can then try swapping injectors and try to duplicate the symptoms so as to isolate it.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!