Tech, Repairs, Upgrades => Capri N/A 89-94 => Topic started by: Pappy T on August 17, 2017, 09:55:15 AM

Title: 3700 rpm stumble
Post by: Pappy T on August 17, 2017, 09:55:15 AM
Hi all, at wits end over this thing...3700 RPM and it doesn't want to run right. Idles and runs great up to that point. Replaced : coil, cap and rotor, fuel pump, pressure regulator, fuel filter, cleaned air related parts, tested all kinds of other parts...all to no avail.
Anyone ever had this situation , I'm more than willing to take on any suggestions  short of arson !  Thanks
Title: Re: 3700 rpm stumble
Post by: chrispoe on August 17, 2017, 12:54:10 PM
Have you hooked up a Fuel pressure gauge and verified proper pressure?
Title: Re: 3700 rpm stumble
Post by: Pappy T on August 17, 2017, 01:01:16 PM
I did, that's why I put a new regulator on it, wasn't holding pressure . Doesn't get over 34# idle or higher rpm .
Title: Re: 3700 rpm stumble
Post by: SHOwn on August 17, 2017, 11:27:02 PM
Hey Pappy, sorry to hear your car is giving you trouble. The FSM does spec fuel pressure range from 34.0 to 40.0, so could your pump be underperforming? The only other ideas I have are plugged exhaust or timing off or a bad vac leak like when my PCV disintegrated on my 86 Escort GT. Maybe someone else has better knowledge though. I can't remember, is yours an NA or a turbo?  It might be that module in the dizzy, but usually the car just quits.
Hope this helps...
Title: Re: 3700 rpm stumble
Post by: Pappy T on August 18, 2017, 08:27:23 AM
Thanks SHOwn, did replace fuel pump , 2nd one in 2 1/2 years , pressure tested with little pressure and replaced pressure regulator, filter too...nada ! Did re check timing , new timing belt , water pump, idler pulley etc couple years ago..all good there. Did all the vacuum hoses - good.
Am leaning toward checking - testing cat converter, would like to get Co2 sensor out to test cat without pulling it out. Don't see cat being issue because of consistency of stall at rpm , 3700, but I guess it's a process of elimination !
Don't recall name of external part on distributor , sensor of some type If that is related ( NA motor ) would like down test procedure on that..more investigating  :-X. Any more ideas would be appreciated . BTW, it only has around 52,000 miles on it, pretty good shape, barely any rust on body too . Thanks again !
Title: Re: 3700 rpm stumble
Post by: NomakeWan on August 20, 2017, 05:12:46 AM
Did you check voltage to the fuel pump connector to see if it's seeing full current? I know the Miata guys sometimes have issues running pumps due to the length of the wire run from the battery, and will end up running relays there instead. Worth a shot to check if you haven't already I suppose.
Title: Re: 3700 rpm stumble
Post by: Pappy T on August 20, 2017, 08:16:03 PM
I'll give that a shot as long as my back seat is partway out...know the numbers by chance ? Thanks !
Title: Re: 3700 rpm stumble
Post by: Pappy T on September 19, 2017, 11:03:36 AM
Can anyone give a little more info on the throttle position sensor ? Trying to test it out and come up with conflicting 4.9 volt in closed position and ohms are off the wall. There were some pics on another thread but they're blocked out . By  chance can it be adjusted to come within specs ? Most everything is pretty much where it should be but it still putzes at 3700 ! I'm somewhat follicly challenged and don't want to end up with the Yul Brynner look over this thing .... Thanks !
Title: Re: 3700 rpm stumble
Post by: JJ on September 22, 2017, 03:13:20 PM
i posted here tps values a few years back. there are two ways to set. one with voltage and one with resistance...

from: Replacing an engine
on: July 04, 2011, 01:49:00 PM

I'm not sure I've heard of a ground causing the idle to not be right, but it does give a stumble while driving.... thermostat ground seems to be a common culprit. I had a problem, and even though I cleaned that ground, it didn't go away until the thermostat was actually changed... go figure.

Did you get the TPS set correctly? When mine went bad it had a variable idle. there is a resistance and voltage check. The slots where it mounts make it turnable slightly, and it needs to be set correctly. I know when Ford replaced my TPS they told me the voltage setting. To adjust, voltage should be between .66 and .7. mine was set a .67v.  they tapped into the wire to read the volts.
Title: Re: 3700 rpm stumble
Post by: Pappy T on September 25, 2017, 10:11:14 AM
Thanks for the input JJ, Replaced ground wire ends a while back because they were pretty nasty, re checked them this weekend..good. Also tried adjusting TPS back and forth while running, no change. Can't figure out why no voltage change while moving it around , constant 4.6 or 4.7 , must be shot ?  Anyone have a extra TPS around ? Either borrow it to test or buy it ? Google isn't too ambitious in finding one...reasonable .