I can't figure this one out. I am getting bad hesitation while driving. If I drive like normal it is fine but every time I try to push the car it feels like it is misfiring badly and it runs lean (not sure how lean, as I only have a simple AFR guage). I have checked the timing, TPS and alot of electrical connections and everything checks out. This started just randomly one day and isn't the result of a mod, and the car runs fine otherwise. I am at a loss, and it sucks that I can't even pass a slow car.

Car and mods listed in sig

 

Mann I having the same problem right now. Does anyone have a solution to this problem

 

need more info on the car like: turbo or NA, S4 or S5, stuff like that.

 

Put me down for this problem as well. I have an 87 N/A. The problem appeared about a month ago and has gradually gotten worse. I changed and set my TPS (cause it was bad), but this didn't fix it. Watching my throttle position on the SAFC, every time I stomp it past 60%, my A/F lights go completely out, and the car stumbles like I hit a rev limiter. Could it be the injectors are not firing?

 

Possibly check your AFM?

Fuel Filter and Spark Plugs?

Every now and then i get something similar on my 88 n/a, I get it on the highway now and then just cruising except mine is usually a complete cut in power, almost like a fuel cut. doesn't bother me to much since I have not done maintenance on the engine in a while and I have a fuel filter thats over 2.5 years old. Spark plugs that are just normally cleaned and not replaced. So I have some obvious places to look before I start to worry.

this morning it was really bad. I hit about 2500 when the engine was cold and I had instant fuel cut. I say fuel cut cause thats what it feels like. I have a feeling it was running lean. I had my AFC -4 at about that point and once I brought it up to -2 like I did before, it was fine. -4 usually runs ok though.

I have to put my fuel pressure gauge back on and take the engine for a spin to see if the fuel filter or other fuel related part is actually the culprit. I will let you know.

 

you need to check your fuel pressure while under load (driving).... to do this get a fuel pressure gauge and run enough hose to where you can run it out the back of the hood (in between hood and windshield) and tape the gauge to the windshield... if you dont have one you can build one with an air compressor pressure gauge, 3 way barbed tee fitting and a couple feet of EFI rated hose...

fuel pressure at WOT should be around 45 psi i believe, check the fsm to be sure

 

ITs possible that all of you are having this 3500 - 3800 rpm Hesitation. Check ground points or

Search 3800 hesitation

good luck with the problem

 

Mine is not 3800rpm, it happends no matter what RPM im at. 1300, 2000, 3800, 5000, 6000, 7000, it doesn't matter. Mine is a very violent power cut and I believe its still fuel cut to all injectors at the same time. Feels like you are accelerating and then turn the ING to off and then back ON again.

I did some troubleshooting, fuel pressure was good under load even with my almost 3 year old fuel filter. AFM's voltage to the ECU was good, Ignition is fine, I found out that you can run and drive your engine on ONLY trailing coils. Many say you can't, well, I just found out otherwise. I wanted to check to see if the leading was cutting out. Trailing was not cutting out since my tach and rpm on the SAFC was still giving me readings while this few seconds of no power took place.

Checked grounds for the ignition and the fuel system, all were good.

I decided to throw in a different ECU and the problem seems to have gone away so far. Crossing my fingers. If it comes back or doesn't come back I will still throw in the other ECU and check the fuel injector pins with LEDs to see if its that.

I hooked up a MM to my o2 sensor and I found that if one rotor is not firing then the reading from the O2 will be lean. I think I did the same to removing the trailing wire and found the same results but I will have to check this again because I have over 30,000 miles on the sensor and from a little playing around, I don't think it is as accurate as it should. Don't say "Its a narrow band so its not going to be accurate" because it can be accurate within a small range.

 

Check Plugs (make sure if the bottom of plug isnt burned out),

AFM Pins are touching and clean.

TPS (if it is correctly setup)the good old 12volt LED lights. always does the trick.

 

Drove around all day today and put some good loads on the engine and everything is still fine.

If it really was the ECU, that kinda sucks, I swapped in the previous ECU because my BACV was not working with the original one, now im back to no BACV but a drivable engine

 

weird. I was going to say vacuum leak....nasty one.

 

^ I do have a vacuum leak Its nothing to worry about though, raises the idle up a bit but engine runs perfect. One day when I have time to pull the S5 UIM, I will fix it.

Today while driving with the previous ECU I was shooting flames pretty good. I would go WOT, rpms would hit around 3500, loose all engine power for a few seconds still at WOT and the engine would come back... BANG, go out again, come back... .BANG!. hehe. Scared everyone behind me they all moved over and raced past me. I did the same on the highway except I went into 3rd from 5th, brought it up to 6000 and lost power for a couple seconds then BANG, BANG and started accelerating Sounded like a 2 step

 

Looks like my AFM is bad. With the flap all the way open, my SAFC only reads 12% airflow.

 

Check the sweep in resistance values of the TPS & AFM.
The idle setting can be perfect, but it there is a bad spot in the signal as you open the throttle the ECU will go nuts & give fuel cuts.

 

Do not go by the percentage, go into Sensor Check and look at the voltage. Should start around 3.8v and drop down to below .30v. The percentage with the AFC is weird, mine works but flapper all the way open, the safc says its 60%. Volts still drop though.

I find trying to do a sweep on the AFM with resistance is pointless, the resistance jumps around so much. I tried 2 different AFMs with the same results, I don't know why it would do that and don't understand it.

Best way is to check the volts at pin 2E at the ECU on a S4 or 2B on a S5 and do a sweep check for volts.

 

hey i just bought an 88 FC witha 13B motor it has the same problem
at around 1800-3500 it sounds like is missing .
and when i stop at a light while im in park (its automtic btw) it will shut off

heres what the car looks like, i'll make a video and upload it soon , i hope its a fuel filter.

oh btw i found this site useful

if any of these work let me know please http://wiki.answers.com/Q/FAQ/928

 

oh and on my stock gauges it has a fuel pressure gauge it goes all the way up when i rev it up , or when im on the highway

 

Ok, thanks for all the suggestions, but shortly after posting this problem I found the culprit. I happened to be that the Pulsation Dampner was leaking alot. I switched it out with a banjo bolt and it fixed the problem. Luckily it didn't start a fire in the 2 months I was driving it like that. All is well now and the car runs better than it has in a long time. Oh, I also had to switch out the o rings, seals and pintle caps on the injectors, as they were so brittle they shattered when I removed them.

 

check to see if your fuel tank has crude in it, flucsh the tank and check your intake air temp sensor, tps could also be the culprit, as all the above was my problem and it had the same symptoms as you