hi I have a 91 formula with a 305 tpi 5spd the car is mint as far as the body,paint and interior is conserned and until this happed I thought I got it for a steal at 3,000 last week. This problem has been already brought to 2 mechanics who spent a good amount of time on it but luckily they are freindsof my family .

The problem is that when the engine heats up the car will run rough and then if let idle for a minute or so it will stall and not start back up until the engine is cool to the touch. if i give it about 2 hours to sit it might start but if the gas is pressed it will choke out and stall. WHEN THE CAR IS COLD IT RUNS AWESOME here is all the things the mechanics and I have done

i replaced the ignition module in distributer, new distributer checked all plugs/wires

a mechanic did a full diagnostic and all he could get was the comupter code as it was dieing we replaced the computer and that wasent it i have spark when it doesent start and fuel pressure is a steady 40psi it seems liek all 8 injectors stop fireing causeing the car to stall

also when we replaced the computer we didnt replace the prom chip could that be it?? sorry this is so long i am despret an no one seems to be able to figure this out please help thanks

 

Have you looked into the EGR system at all?

 

If it were egr, I would think it would start, just run really, really, bad.

Need to know if your injectors are pulsing when you have the no-start condition. Buy a noid light, with your employee discount, should be downright cheap.

See what happens next.....

 

Had this happen to a friend with a 90 IROC 305. All the injectors went south and were bad when hot but when cold car ran good. Test the injectors with an ohm meter when hot and post results.

 

Check the IAC solenoid.

 

well when its in a no start condition the injectors are not pulsing but the car still gets spark via wires/plugs

my mechanic is about to give up do to the amount of time and diagnostics hes done. im bringning everything wirtten here to him and if we cant figure this out today, i may just be alone working on it till i get a gm appointment and throw my money away

is it possible i will never figure this out? how many things could it be?

 

Like what was said earlier, check the resistance on the injectors when they are cold and when they are hot. If they are below 12-14 ohms then replace them. If this is not the problem, then start checking your wiring. You might have a wire that is broken or is getting hot. If my memory serves me correctly, there is a wire coming off the distributor that signals the computer when it is firing. This is how the computer knows when to fire the injectors. This wire could be bad.

BTW. I not sure about that injector test. You might want to check a manual.

 

could all the injectors be bad?
that wire you are refering to had about 20 test light holes and i replaced it
could it be the prom chip?
he couldent figure it out so im all on my own for now and if he couldent figure it out i dont know if i can

 

When the car is at a non start point, try pulling one of the injector plugs and test light the circuit while cranking the motor. DON'T use a regular test light, use a computer and sensor test light. A regular test light can and will fry your computer.

At this point you know your fuel injectors aren't firing. Then the thing to do is work backwards. If you aren't getting a curcuit at the harness then keep going backwards. Grounds, connectors, wires, etc. All the way to the computer, until you find a problem. If you still don't find a problem, then check the reference wire tha t triggers the computer to fire the injectors, from the distributor all the way back to the computer. You should be able to do a curcuit test on that wire, just as you did on the injectors. If you still can't find a problem, then find a friend with a 305 TPI car, and put your computer in there car. See if it does the same thing.

 

I have the same problem!! I changed the module, fuel pump, fuel filter, and other various things. I wanted to see if it was something small b4 I changed the injectors. Unfortunatlly it may be the injectors because I am all out of ideas. One other thing it may be is the wiring in the engine compartment. Lose connections, hot wires! I dunno!!!!AHHHHH

 

ws6formula, did you let the car sit (not drive) for a period of time and did it still shut off? It sounds like I have the same problem but when I left the car running for an hour or so, it sisnt shut down! I am not sure if we have the same problem, but it may not have anything to do with something getting HOT! It must be something only when it is driven. Correct me if I am wrong! I am still confused!

 

well i made the gm appointment for wednsday... i did exaclty what dahaus said and it all went back to the computer. i replaced the computer witha new one and no difference.

one question tho when i change the computer i use the old prom should i get a different prom?

also i heard an intresting theory from a mechanic, he says he thinks there could be an oil leak onto a sensor in the crankshaft or camshaft? and the reason it will only start after some time is the oil needs to drip off?

and also when the car does run and begin to show problems it wont go above 2500 rpms before what seems like starving for fuel and the problem seems to be getting worse but that may be due to me running it until it dies more and more often

thanks alot for the help and Milanzo if and when the dealer fixes mine i will let you know by the friday what it was so hopefully u can save the 5-8 hundred im most likely paying

edit: milanzo if i let the car sit and heat up enough depending on the weather (heat) it will eventualy die out

 

Sorry I couldn't help more. Hope everything goes well with at the mechanics. Let us know what it was when it is fixed.

 

well the dealership read the injectors ohm readings and while they should be at 12 ohms there all at 2-7 ohms. they tried to get me to pay them 1600 to replace all injectors and that wasent gonna happen. m taking the car and im about to have a mechanic i know put them in

what are the odds all injectors went bad? the tech at the dealer said the injectors could be melting together and arcing and grounding out on eachother but he wouldent guarentee the 1600 dollar fix being the solution thats why i realy cant trust them not to completly rape me.

this seems odd could there be another readon for that ohm reading? thanks

 

If it's the same mechanic who said this...

Then run away. Fast. There are no crank or cam position sensors on your engine.

 

I think he was probably using the wrong scale, if your injectors read that low your car would not fire period and your computer would be toast. Good 22lb injectors read between 16-17 ohms below 10 is unservicable, Im not sure what your 19lb injectors should read but a search will tell you. You should check them yourself to verify this reading. I have burnt injectors twice both times it was 3 at a time, when they do go if one is very bad it will keep all of them from firing. If you unplug the very bad one the car will run on the other 7, so unplug them one at a time try a couple times to start it and see what happens. I dont recomend driving it this way but it is a good way to diagnose it. And 1600.00 to replace them is Horse****, Last time mine went i got 8 used injectors for 50.00 on here and put them in myself. It was a pia but it was free .

 

My friends injectors were around 8 and we ended up using a new set of Ford 19 motorsport ones from summit and they work great.

 

So basiclly, the problem is your injectors?? Can injectors for a 305 work on a 350?

 

Yea but it'll run kinda lean with out a AFPR. Antyhing more then a stock 350 then you need the stock 22's with a AFPR or larger.

 

At 2 ohms each injector will draw 6amps, 6amps x 8 injectors is 48 amps, each set of 4 injectors are protected by a 10amp fuse.
Are you're fuses blown?

Use a noid test specifically made for fuel injectors.

You can't use a different chip unless is has the same program burn on to it.

To use 305 injectors in a 350 you would have increase the fuel pressure (~60psi to get 22lb/hr,) but too much will drive them beyond the 80% duty cycle at WOT. You'll get a lean condition not good especially at WOT.

 

Again, I seriously doubt ALL of your injectors are at 2 ohms i would double check that.

 

Do you have a multimeter? If so, just verify what the dealer told you before doing anything else. To check the injector's resistance, take an OHMS reading across the two electrical contacts of each injector. Do it first while it's cold and starting okay. Then do it again once it gets warmed up enough to start acting up. Both readings should be in the 12-16 ohm range. I'd do that before swapping them out if it was me..... (I'd also check my new ones before starting the swap, too!)

Just my two cents with a nickel's change coming back.....

 

well i went back and they said my highest ohm reading was 8 ohms and that injector 6 and 8 were at 2ohms. im getting the injectors hopefully for about 100$ which isnt so bad and I figure il just replace them anyway and who knows that might solve the problem.

the reason for my huge consern about this is that this is my daily driving car and its been down for almost a month now... also i would have the car here at my house but I had tried and failed to fix it for about a week and a half and also i dont wana screw anything up because this car is as close to perfect in a thrid gen as i could ever get with a stock 305

thanks alot for all the imput, im getting the injectors tommorow but they might not be put in till monday il be sure to keep you all informed though

 

That sounds a little bit more reasonable, but those injectors are toatally toast im surprised you havent ate your ecm yet.

 

Be sure to check the "new" injectors you're getting since at that price they're probably used ones. Make sure they're 19 lb/hr injectors as well or you'll need some custom prom tuning.

 

Curious, doesn't it pay to just change all of the injectors?? Won't the same problem come along sooner than later?? A new set is less than $300, and most of us work on are own cars, so we wouldn't be paying labor. Also, putting in used injectors is like putting a band-aid on the problem, not fixxing the problem. I dunno, just my 2 cents!

 

I just started to have the same problem, cold start runs smooth, after 4 minutes it misses and runs rough. ALL the sensors and distributer parts have been replaced within the past six months, IAC been checked. I've checked the plugs and it's running rich, I have a afpr set at 42psi, before the problem I had it set at 48psi for 2years. My fuel pump is sounding weak on start up. The only thing I've done recently is change my transmission pan. All of the injectors are firing checked when cold. It's sound like something is wrong during closed loop mode.

 

I agree with 91b2l. I really don't think its the injectors, or injector, in this case! There is something that you are missing, something stupid. The injectors should not opperate differantly if they get hot!

 

Do a search on injectors. You will find once they are hot the ohms change if they are bad.

 

Where does one find this info? Is it in a service manual or something?

I still think it'd be worth at least looking into the egr, I've seen some goofy stuff with the map cars and egr.

 

Yes, in the manual.
In 91B2L's case the egr would have to be a sticking problem because the EGR isn't used at idle.

 

That would be Ohm's Law, using 12VDC as "E" and plugging in the various resistance numbers he used for "R" to calculate amperage "I".

E=I*R

 

I think he meant where to find the injector specifications.

 

I think I found the problem with mine. I took the plenum off to get to the EGR, when I went to disconnect the hard vacuum line from the egr to the solenoid, it was broke on the solenoid side. I decided to get a new solenoid, noone in town had one, so it will take a few days to see if it was the real problem.

 

ehh I dunno. That wouldnt cause a hot start problem. Maybe a little rough idle with that small of a vac line disconnected, but not the problems your talking about.

I'm still voting injectors.

 

Whenever I read about problems associated with the temperature of the car (aka it runs a certain way when hot or when cold) it gets me thinking about the ECM. There are two main modes that the ECM runs in, open loop and closed loop. There are other modes like limp home, but you're usually not gonna see that unless something extreme happens. Anyway, so when you first start the car and everything is cool its running in open loop. Inside the ECM there are a bunch of temperature related conditions that have to be met for it to switch to closed loop. When it switches to closed loop it now begins to use the data from the sensors to manage the engine. So if things suddenly change when you reach a certain temperature, theres a good chance it went to closed loop, which means something is wrong with one of the sensors. There's a good way to check this, insert a paperclip into the A and B terminals of the ALDL port while the car is running and watch the SES light. If it blinks slow, about once a second, then its in closed loop. If its blinking fast, then its in open loop. I recommend you do this to find out what mode the ECM is in when this problem happens. From there you can eliminate or add possibilities as to why this is happening. Be sure not to start the car with the paperclip in the ALDL plug.

I also recommend you either buy or barrow an ALDL scantool from someone. Then you can see on one screen all the values of all the sensors, and right away see if some of them are off. Its possible for a sensor to be off as in returning the wrong values and not cause the SES light to go on. SES will only go on if you unplug the sensor or it gets way jacked up.

From reading about your problems I would suspect the O2 sensor. Faulty readings from the O2 sensor can cause the ECM to dump too much fuel or not enough. Car gets hot, ECM goes closed loop, gets some input from the O2 and calculates how much fuel to spray, sprays the wrong ammount. *shrug* You could eliminate this possibility if the problem is happening in open loop.

 

well it turned out to be all of the injectors whole job cost me about 900$ but it was worth it witht the warrenty. thanks for all the help and suggestions i hope this helps someone else out in my situation.

finaly i get to drive it everyday i just got it back today and i cant wait to get in it every time

 

ahhh haaaaaaaa....... lol

 

Found the problem, I did the injector ohm test the results are

#1 16.2
#2 17.2
#3 16.7
#4 16.6
#5 16.4
#6 16.9
#7 16.1
#8 5.1

Now i'm looking at getting a set of Ford injectors #24 and a custom prom. Thanks guys for all help and input.

 

I have the same probelm, so I will most likely be doing the injectors, but quick question. I have the 305. I plan on swapping a 350 in the future. What injectors can I use for both engines?

 

305's came stock with 19lb injectors 350's came with 22lb. You may be able to use 22lb injectors on the 305 but it would probably require some prom tuning and an adjustable fuel pressure regulator.

 

would I be able to use 24# injectors with an AFPR on the 305?

 

Yes, you're able, the static pressure needs to be around 28psi but, your spray pattern is gone to suffer, not to mention the gas mileage.

 

Well, I am not going to be using the car anyway, so I might as well wait for the 350 and just do everything then. Thanks for the help!!