Stalling on deceleration?

rusty ol ranger · Oct 7, 2018

87 2.9/5sp.

Got 90% of my issues figured out. Evendently i had 2 bad coils (the original plus another one i had) and now it runs good.

Changed coolant temp SENSOR, no more richness.

However, it still stalls if you use the engine to slow the truck. If you mash the clutch after downshifting to slow down, the damn thing stumbles down and quits, unless you feather the throttle then it comes right back and is fine.

Any ideas?

RonD · Oct 7, 2018

Computer uses IAC Valve to set minimum RPMs

Computer shuts OFF fuel injectors when coasting "in gear" if RPMs are above 1,500, one of the benefits of fuel injection, 0 fuel used when coasting

Coasting is when TPS(throttle position sensor) is under 1 volt, .69-.99volts, foot off the pedal

In a manual "in gear" is when clutch pedal is up, computer gets 5volts through clutch pedal switch, 0volts when clutch pedal is down, that's "neutral"

rusty ol ranger · Oct 7, 2018

I tested the TPS already its functioning properly. So its pry the clutch switch then. Would this explain why the RPMs dont always "hang" between shifts

Bird76Mojo · Oct 7, 2018

Sounds like a vacuum leak

RonD · Oct 7, 2018

Not sure if the RPM Hold was in 1987 software, thought it was just 1995 and up, with new computers

rusty ol ranger · Oct 9, 2018

Well, obviously whatever is causing the stalling on decel is still an issue somewhere else because it still floods out.

Intermittiantly.

After getting it back from my mechanic (who discovered the bad coil) obviously i took it for a drive, not to far, maybe 15 miles, everything seemed great besides the stalling when you downshift.

Brought it home, parked it for 2 or 3 hrs and decided to go visit the golden arches. Everything was fine untill i had waited about 5 min in the drive thru line, it started stumbling around and smelling gassy, hit the throttle, cleared its throat it was fine for another 5 min or so. Once i got back on the road i had no issues till i got home, this time it ran about 2 minutes then flooded and died, but fired right back up.

So i yanked some (good) parts off of rusty #1, changed the coolant sensor, took it out for another drive. Brought it home, let it idle for literally 45 minutes without so much as a hiccup.

Cool, got it fixed.

2 or 3 hrs later took it up town, pulled in my driveway, and guess what? Flooding.

Next day i swapped the MAP and AIT for shits and giggles. Drove it around town for 30-40 minutes, brought it home, let it idle again 1/2 hr. Didnt even stumble.

Let it sit 2 hours, went out, and took off down the street, another minor flooding episode when i rolled up to a stop sign, cleared it out, brought it home, and sat and idled for another 20 minutes with no problems.

WTF is going on here??????

Bird76Mojo · Oct 9, 2018

Almost sounds like what my 86 2.0 was doing when the cat was clogged. It still had great exhaust pressure leaving the tailpipe too. I didn't find out until after I sold it. We left it idling while we went to the gas station for snacks. We came back after about 30 minutes of talking to someone at the station and we thought it was on fire. It was smoking really bad underneath, and it had nearly liquified the rubber/vinyl floor. Cat was glowing cherry red.

I don't remember if it was stalling on decel or not.

Anyway, just a thought...

GB

rusty ol ranger · Oct 10, 2018

When all these issues started a bad cat was brought up....

But...
1- It passed a vaccuum test.
2- Half the gasket is gone anyways.
3- Its never gotten hot/doesnt rattle

wildbill23c · Oct 11, 2018

Fuel pressure regulator maybe dumping too much fuel causing it to flood.

dirtymike · Oct 20, 2018

what is the fuel pressure at idle and at 60 under load.

rusty ol ranger · Oct 25, 2018

Hey guys, sorry aint had time to check in....been alot going on....

Either way, ive tested the fuel pressure at idle its right around 40PSI, no way to test it at 60.....

I have since replaced the O2 sensor and it is running better. But i have finally figured out the rhyme to make it flood, just not the reason....

It runs great cold, but right before it goes into closed loop youll hear it kind of start popping and sounding/smelling rich. Then as it hit closed loop the idle drops (seems like its idleing low however, but maybe not), it will sit and idle all day long....BUT...

If you rev the throttle a bit and come up on the clutch (like to roll ahead at a stop light) then put the clutch back in itll go to stumbling around, rich as hell, till you blip the throttle and it clears right up.

It still does it on decleration as well, as soon as you hit the clutch after engine braking itll stumble and take to fits, and sometimes stall (unless you blip the throttle some), if it stalls itll immediatly fire back up and run great (athough belch a cloud of black smoke worthy of a tuned 7.3) untill you do one of the above things to piss it off.

I have no codes. Ive changed every sensor on the thing except the TPS cause it tested good. Atleast i think, but wouldnt that cause it to act up cold as well?

Im totally lost here and about ready to give up on it. I need suggestions. Im thinking of replacing the injectors/FPR but ive never screwed with that before so im exhausting other options first.

Help please.

bobbywalter · Oct 25, 2018

reading the ect and map when its doing it what you need to do....

assuming the compression is still good on hot test and there are zero vacuum issues..

raise the idle and drive it. i am thinking you have mechanical issues and sensor problems.

rusty ol ranger · Oct 25, 2018

bobbywalter said:
reading the ect and map when its doing it what you need to do....

assuming the compression is still good on hot test and there are zero vacuum issues..

raise the idle and drive it. i am thinking you have mechanical issues and sensor problems.

Swapped the map with rusty #1, no change.
Tested vaccuum all was well there. I can check it again but it was a steady 17 or 18 and didnt do anything funky.

My mechanic thinks its a valve, but he also thought my 77 had a bad valve when all it was was a bad plug wire.

I guess ill get a compression tester. Ida thought a bad valve would have showed up on a vaccuum test and it doesnt seem to show any other signs of bad rings or anything.

Ill check compression and post what i find out.

bobbywalter · Oct 26, 2018

without testing / watching the map...or actually function testing the sensors...swapping them means nothing.

leave the map unplugged. see what it does....may just be shitty ground/return

the valvetrain when well worn is going to change the complete airflow and running dynamic of the engine....a properly functioning map with incorrect airflow with god knows what else is going to result in drivability issues.

plugs/wires/hall effect/tfi need to be working right and supplied with clean power.

any ground issues alter pcm communications..

87 2.9/5sp.

Got 90% of my issues figured out. Evendently i had 2 bad coils (the original plus another one i had) and now it runs good.

Changed coolant temp SENSOR, no more richness.

However, it still stalls if you use the engine to slow the truck. If you mash the clutch after downshifting to slow down, the damn thing stumbles down and quits, unless you feather the throttle then it comes right back and is fine.

Any ideas?

pretty sure i would just raise the idle and drive it if everything checks out..

i would do a solid hot compression test and leak down along with measuring the valve events before spending a nickle on one of those turds.

i suspected injectors months ago based on what your reporting as long as the halleffect/spark condition and fuel delivery were spec. 38-42 at idle and 33-35 psi wot is good.

wouldnt buy em till i knew it was solid though.

parts geek has good deals...

Part Number: 4974-02543622
Brand: Replacement
Notes: (SET OF 6) FUEL INJECTORS
Product Remark: Kit Includes (6) Fuel Injectors
Condition: New

Our List Price:
$87.95

thats cheaper then servicing them...but they may only last a year...or not work correctly right out of the box...

service shops are still out there though.

http://injectorrepair.com/contact-us/

kimcrwbr1 · Oct 26, 2018

When the throttle butterfly is opened the computer closes the idle air control try cleaning around the throttle body butterfly? To test it run the engine around 1500 rpm and unplug the idle air control then let it idle. If it stalls adjust the throttle butterfly stop to slightly open the butterfly to run around 650 rpm. Then plug the IAC in and the computer should control the idle speed. Thats called the anti diesel stop adjustment when you let off the throttle quickly the fuel has air to burn until the idle air valve opens.

Stalling on deceleration?

2.9 Mafia-Don

Official TRS AI

2.9 Mafia-Don

Well-Known Member

Official TRS AI

2.9 Mafia-Don

Well-Known Member

2.9 Mafia-Don

Well-Known Member

Active Member

2.9 Mafia-Don

TRS Technical Staff

2.9 Mafia-Don

TRS Technical Staff

Well-Known Member

Sponsored Ad

Sponsored Ad

Member & Vendor Upgrades

Truck of The Month

Recently Featured

Follow TRS On Instagram

TRS Events

25th Anniversary Sponsors

Check Out The TRS Store

Sponsored Ad

Sponsored Ad

Sponsored Ad

Amazon Deals