My car is still having the problem its had for months now except its even worse. It would burble and sputter when the gas was let off and have a slight miss will climbing the RPMs. So the other day I cleaned out the throttle body and IAC and it got even worse. Now you can feel bumps at idle and there are major skips while climbing the RPMs. Performance is all but gone with the skipping. As soon as you let off the gas the car stumbles down. I have replaced the spark plugs, plug wires, cap & rotor, fuel filter, fuel pump, and the filter on the fuel pump. What could this be?!? There are no lights showing on the dash. I am really stumped and getting very irritated since this problem just won't go away. Please anyone give me their advice. The car is starting to run really bad and I can't stand driving it running like crap. Thanks for any help given.

 

Have you checked the coil?

 

Sounds like another case of the multecs... check your injectors.

 

What should I look for on the injectors? That might be it. I also need to check the coil but it looked fine a few weeks back when I checked it.

 

You check the resistance across the injector and make sure its within spec, which i believe is 16 ohms. You also need to do a fuel pressure test to make sure none of the injectors are leaking. In addition to this i'd also check to make sure your car has good vacuum and check out your MAF as well.....

 

If the MAF is bad wouldn't it cause the check engine light to come on? Or does it do this only when the MAF is completely dead?

 

What does that measurement prove? That an injector is stuck shut or stuck open? I've got a leaking injector, and would love to know which one is leaking before I pull the rail out. Thanks!

 

The very best way to check the injector ohm's is a sat overnight ice cold engine ... They need to be within a couple of tenths of each other. 15.9 - 16.2 ohms on 16 ohm injectors... You will get your best results testing them this way when looking for weak or bad injectors...

TomP, Your problem is probley not goung to be found this way.. might.. but doubtful.. If it's leaking you get a missfire ? Pulling spark plugs isn't fun... but probley the best way. If it misses long enough you can kill cylinders with a test light.. Either that or if your sure that the electrical is good to the injectors, yank the rail and leave it connected to the fuel lines and pressurize the system..

 

you might want to check out my post...starts out..."fluttery RPMS...on my last nerve" osmething like that....on this same board

 

I had a very similar problem on my 92 305tbi RS just this past summer. I did everything you did (cap, rotor, fuel pump (what a pain in the ....that was!), etc.) I even rebuilt the throttle body. It got especially frustrating becuase I didn't get any error codes from the computer. THE POINT: It was the pick-up coil on the distributor (about a fifteen dollar part)! Assuming you have checked, corrected, and cleared any error codes, it might be worth the time and minor cost to make sure you don't have the same problem. If you have not, or are not familiar with how to, check the codes, it's easy. You just have to bridge the A and B terminals on the computer plug under the dash and interpret the blinking sequences of the dash light. A Chilton's or Haynes manual will walk you through it and tell you what the various codes mean. (I don't want to insult your technical expertise. You probably know all of this already.) Best of luck. Let us know what the final solution is.

 

The resistance test only checks the electrical characteristics of the operating coil of the injector solenoid. It does absolutely NOTHING[ to identify a stuck, clogged, or poorly flowing injector. Rochester and Bosch injectors are serviceable in an electrical resistance range of 12-18 ohms. The design resistance is 16 ohms, but there is quite a tolerance. An injector can test "good" by that method and still have a stuck pintle, clogged tip or screens, poor spray pattern, internal leaks, etc.

Since the injectors are all banked in parallel, any differences in the resistancees across a bank are inconsequential as long as the minimum resistance is present. All the ECM sees is a single load from each bank of about 2 ohms, and energizes that load accordingly.

Incidedntally, Multecs were not installed on 1987 TPI engines, as far as I am aware. Stock injeectors were likely Rochester, and possibly Bosch.

Injectors aside, one only needs to do an archive search to discover that an altered MAF can and will provide erroneous readings at low- and part-throttle flows, primarily due to the uncontrolled air flow through the body and around the sampling tube.

 

Well I am going down to my friends shop tomorrow evening to scan for bad sensors so maybe I will solve the problem there. If not then I am in some trouble. Thanks for all the replies so far though.

 

The 1987 would either be Bosch or multech unless it is some kind of a late breed but pretty doubtful to be a Rodchester untill 88.
Vaders right about the injector stuck, cloged ect.. But on the other hand to put it simply.... The ECM carries and varies no load to the injectors. The ECM only supplies the ground circuit to the injectors. The way the circuit varies in load is through the amount of resistance the circuit provides from the injector resistance.

If you ohm injectors ICE COLD.. That means overnight. If they are all good they will be within a couple of tenths of each other.
It you have one or two that are a ohm off or so, get rid of it/them they are no good.
So far the only cases I've found it ness. to test injectors overnight the driveability problem was hot and under a load. The car would miss and run really rough under a loaded condition and the most recent was a 89 Camaro TPI 5.7
This info was provided in my factory service training in San Leandro, Ca.

 

Not to argue, but I must have a REALLY odd '86 TA. I know they are a bastard-child to begin with, but the stock injectors have the "RP" logo on them, IIRC. And according to my service manual, the acceptable resistance range drops way down to 12.9 ohms on the coils.

In any case, don't expect to find a lot with your ohmmeter. You'll have far better success with a power balance test of the injectors to locate a defective one, and even at that you cannot find a leaking one very often. The most assured method is to remove, clean, and test them. For just ten bucks apiece, I'd suggest getting professional help from Cruzin' Performance, but you can remove the fuel rails and test for leakers in your garage.

Before you are ready to blame the injection system, be absolutely certain the ignition system is reliable and you have good compression in all the holes.

 

I've fought problems like this before...the easiest and cheapest way IMHO to find out what's up is to go to the ignition system.


I always try to keep a spare distributor around for things like this.


To see if it might be injectors, go to NAPA and grab a can of Seafoam cleaner. Dump half the in the gas tank, suck the rest through the throttle body via a vacuum hose.

If the skip is still there, I'd look towards the ignition system myself.

Modules go bad, pickup coil's go bad, etc. This is where a factory GM service manual is invaluable.


HTH

 

Hey Vader, I don't want to argue. Reality is that I thank you and lotsa people just like you in this site that have helped me to make my Formula not just fast... Man it is off the hook...LOL

It screams and it was fairly fast with thefactory set up 305. I've been a auto tech for about 17 years or so and I do driveabilty and electrical 8 hours a day. I use to do everything but hell i'm getting to old to do engines everyday so I havn't done heavy duty/engine for a long time now. A friend turned me onto a rebuildable late model 350 short block and I went threw it. Had my 305 heads done and put them on it. Bought a new roller cam and lifters and the combination stunk and it also vibrated. Thanks to bad advise from other technicians, a sprint car driver and a mechanic and and a certain machine shop that couldn't balance an engine if it was already inbalance...it was bad, I yanked it in less than 100 miles and started some research. I found this website, got some books ( Chevy Power, Leginfilter, Emanual ) I went to leaning and finding parts. I built my own AFPR. Another friend that always asks for my help had 16 sets of small block heads. in them were the 993's in leginfelters book. gottum free... Started reading in here about porting heads. Bought a book. Found MadMax's post about porting manifolds and indeed ported and polished everything on top.... but just under 4 inches into the intake. Ported and polished the heads. The pistons I had matched the heads perfectly. Cam's ( the ram jet cam ) seemed not a good choice at the time but now seems to be a good choice with the mod's and adding 1.6 Harland Sharp roller rockers not only does it lope. It pulls really hard... Just don't know yet where it will quit making power. Have not gone that high yet Ohh and btw I was told that the computer would freak if it lope's.. It wouldn't idle at first but it idles perfectly now. It learned it and sounds cool through the trick exhaust .. system is a speed density.

Anyway.. I am very pleased with the out come and I am just trying to give back where I can.. My way of saying thanks to everyone out there who helps make this all go round...


The injector deal.....


I agree with you and I think trans87's problem is probley a plug or wire. I was trying to answer TomP's question about injectors. In all reality I've had maybe 3 to 5 cars in the last 10 years or so that needed a ice cold resistance check to figure out why they stumbled and backfired. All cars were port injected models. As far as the resistance thing goes, Injectors will have somewhere between 12 and 16 ohms resistance depending on underhood temp and the injectors/PCM in the car. If there are 8 injectors on a Camaro they should all read within a couple of tenths.

Say if 7 injectors have between 13.8-14.0 ohms resistance and the 8th has 17.8 ohms. That injector will lean out that cylinder and under a load the resistance gets higher and the ampreage gets excessive which can kill injector drivers in the PCM. That's the only reason to even bother with a ohms resistance test and the test should be checked not only cold but hot too.

What I feel is the best way to test injectors is to hook up a fuel pressure gauge and fire each one individually for the same amount of time and see what the fuel pressure drop is.

 

UPDATE: Ok I went down to Kevin91z's Dads shop. We ran the computer on it and the sensors are all reading ok. We checked the fuel pressure and its right where its supposed to be. Also we checked the timing and it was dead on what it was supposed to be. The wires and plugs are a month old as well as the cap and rotor. We revved it in neutral and you can feel the engine do slight bumping at around 2-2.5k RPM. We are completely stumped on what the problem is

 

I had a vehicle a couple months back that we had tuned up and about a month later it started to studder as it left a stop. I scoped it and it looked ok.. Under a load I found what appeared to be a couple of bad plugs. I decided to replaced them all as I plulled them they looked brand new. Test drove afterwards and the problem was gone... Just for info...

Also.... You sound like a canidate for a cold injector resistance test. It sure won't hurt it to check... Read my previous post about it. all within a couple of tenth's...

 

AAAHAHAHAHAHAHA!!! sorry , i jsut figured mine out FINALLY!

WIRES WIRES WIRES!!!!

i bought a multi meter, checked the wires (found a couple bad ones), checked pick up coil, checked coil,...put on some new wires....and omigod, its good to be home! ha i forgot how it felt to put your foot down with confidence!!!

haha the other day, on my way to the part store (with my awful missing), some chump was next to me in his four door honda accord with rice lights and wheels and a spoiler.....he kept revving....i just laughed it up, like he wasnt worth it, but in reality, i laughed because i knew i couldnt rev without stumbling and backfiring...hahah he so would have taken me tat day
!!!! if i see him again......

i pulled a couple plugs too, looked good, one with a little carbon, but im sure that was recent because of my whole ignition problem....i left them in, gonna replace them over winter brake.

 

I agree with 90Formula-X-F, I had the same problem with my '92 Z28, my old plugs were only one month old, replaced with new ones, problem went away and stayed away. My old plugs were rapidfire's new were bosch 4107. weird.

 

First off I would like to thank everyone for continuing to give advice to me and not forgeting about the post. I really hope to solve this problem soon because I can't stand the decreased performance I am experiencing. Ok back to the problem. I went today and put some fuel injector cleaner into the car and I will see if that has any effect on the car. I know it won't fix it but if it helps it out some then I know its dirty something. The only problem with this car is that it is my daily driver which I need for work and HS If it wasn't for that I would be tearing it apart to see what was going on. It seems to be a fuel starvation problem to me. If you let off right where theres a blip the car will almost stall. Also I can mash the throttle and the car will gain very little RPM but in bursts the car will go normal for a sec and gain then go back to dying. I am leaning towards the injectors being blocked. This problem got as bad as it did as soon I cleaned out the throttle body with throttle body cleaner. So maybe some stuff got coated like the injectors or IAC

 

So far the fuel injector cleaner has given no signs of improvement on the car. I can't figure this out at all. I am just about ready to take my car to the mechanic shop to have them find the problem so I can fix it

 

trans87, I could probley help you fix this.

#1 What spark plugs are in the engine.

#2 Rehook a fuel pressure gauge up to your car and make it start to stall out. What is the fuel pressure reading ?

#3 Can you get it to actup when the cars stopped (power brake it ? ) If so, look for the wire harness behind the ignition coil. It's the main harness that goes down the back right side of the motor above the trans.. it intangles in the heater tubing kinda .. Have someone pull on it kinda hard while your car is sputtering. Does it get better ?

 

What kind of fuel injector cleaner did you use? Most of the stuff sold in auto parts stores doesn't do much of anything IMHO. If you really want to clean 'em, and this is from personal experience, go to NAPA and pick up a can of SEAFOAM. They will know what you're talking about. To a search for SEAFOAM on this site. About $6 a can, works great.



If that doesn't help, I'd splurge and spend @ $1.00 each on 8 new AC Delco spark plugs and try that.

HTH

 

The car has the basic Autolite spark plugs in it. The car won't do the burbling and almost stalling while just sitting and revving. You have to be driving it to do that. Also you can barely feel the engine do the missing while just revving. To feel these problems the car has to be in motion. When the car sputters it sounds like a car with a really lopy cam in it. You know like a 68 Camaro muscle car sound with the lope. Someone also told me that it might be the TC going. Anyone agree with that? I am just plain *** confused.

 

Hey the EXACT thing you are distribing happend to me but I know what it is and i'm not telling you! :P j/k lol.

It was my MAF, picked up one from a junkyard for like 15 bux to fix my problem.

TEST IT OUT!!! Unplug your maf and see if it does that. If it doesnt do it anymore then its your maf.

On my 2.8 bird it would 'miss' when i revved it but when i was driving it and when it got around 2800 rpms it would go back down to 2100~~ and back up again.

seriously unplug your maf and go for a lil drive.

 

Also my problem I hadwith the MAF didn't make the SES light go on.

 

I will try unplugging the MAF to see if that helps. My car doesn't miss when I rev it in neutral, well not where you can hear it but if you put your hand on the engine you can feel slights bumps. It's when you are driving is where all hell breaks loose. While accelerating the car feels like its skipping. Almost like in a stick shift when you don't let off the clutch that well so the car kind of jerks a little. It does the skipping throughout the RPM curve and in any gear. Now if I am going slow and accelrating and let off the car stumbles. Sounds like a car running out of gas. The RPM will dip down a little under 500 then go back to the usual idle spot. Its been doing this problem for a month but the skipping one has been in the past week after I cleaned the throttle body. It used to be a slight blip when cruising in the 2k-2.5k range. So I decided to clean the TB and see if that helps. Well after I cleaned it with the spray throttle body cleaner the car started accelerating like it does now.

 

sounds like my old problem -
I was sorta guessing this -

The MAF measures the ammount of air comming into the engine, so if its not measureing right - or malifunctioning, it would cause the car to give it too much gas - or too little gas either chocking the engine or starving the engine.... marking it want to stall/miss but then it goes back.

I dont know just a guess.... as to why mafs would do that..

 

Yea I will check the MAF. Might be it might not. At this point anything is worth checking out. Thanks for the advice. I wasn't really thinking the MAF because of how the problem showed after I cleaned the TB but who knows. Should the car run normally with the MAF disconnected? Doesn't it use it for the air/fuel ratio? Wouldn't disconnecting it cause the engine to run bad? I know the light will come on and have to be turned off but its worth the shot. I just want to make sure by disconnecting the MAF I will be able to tell if the MAF is causing the problems or will new problems arise with the MAF disconnected.

 

Unplugging the MAF will make your car run richer, but if the maf is toast, it will run beter.
I did it and it didnt hurt anythin.

 

If the maf is cooked, its probally sending the computer some info that is WAY off. With the MAF idsconnected the computer will guess the ammount of air comming in, it wont guess right, but it will be a hell of allot beter then the toasted MAF.
I just dont think its a good Idea to drive around all the time with the maf unplugged. Just unplug it and go around the block.

 

UPDATE: Ok I unplugged the MAF and the damn car wouldn't even idle. I had to hold the gas to keep it alive. It ran rough but then smoothed out. Keep in mind this was me still holding the gas as soon as I let off the car died. So I wasn't able to drive with no MAF because the car kept dying. Is it supposed to do this with the MAF disconnected? Would a bad IAC be my problem? Please any help will be greatly appreciated.

 

sounds to me like youve got a miss under a load. I would like to think its ignition related I would recheck the plugs, Ive never had any luck with anything but Delco plugs for some reason in GM cars. another thing that may be causing it is the ignition module. you said you checked the timing but was that the base timing, what about the timing curve up the RPM scale? take a really really close look at the ignition system.

 

I think I told Kevin, but anyway...
Try disconnecting your TPS. I really dont think thats the problem from what you are describing, but it cant hurt to try it. Usually after doing that, at first it will run badly under acceleration, the more you drive it, the more it'll act like normal. Then you can hook it back up and see if it starts running bad again.

 

Ok today it wasn't idling. I would have to keep the gas down to keep the car alive. Everytime I let off the car would just die. I drove about 55 miles to a car meeting and finally it started idling again once I arrived at the destination. Any ideas on what would be causing the stumbling with the gas being let off, the missing under load, and the ever once in awhile no idle? Man this just gets more complicating everyday

 

I had similar problems, but mine were related to .70 gap splitfires, $5 wires, and a $10 distributor. Fixed them, and it go good now Keep looking, I'm sure you'll find it, and be much the wiser when you do!

 

Yea I am sure by the time I finally solve this I will know everything there is to know about my car. To make things even more wierd is that the car ran fine today. Did the burbling after the gas was let off but no skipping or powerloss. Ran just like it used to. Felt great driving my car again. But this really stumped me and has me worried. There is always a calm before a storm Any ideas? I think I am going to replace the IAC next weekend and check the wires to make sure they are good. A lot of people tell me the MAF might be the problem. How do I properly check that?

 

Ok today the car ran fine too. Still does the stumbling after the gas is let off but other than that it accelerated fine with no missing Why would the car all of a sudden go back to normal?

 

'Cause it gave it's problems to me

Failed emissions (after a $750 shop bill), VSS came loose, and the alternator belt is squealing again...

What did you do!?!



Ahh well... Gotta love emissions waivers availability.