2.9l giving me a headache

[Pix3L8]

Hi guys, it's been a while since I posted about my truck. This past winter the pig died on me at a gas station, crank no spark. Got it towed home and after some inspection found a suspect-looking ignition coil power wire. After I fixed that the truck would start sometimes but kind of struggle for a second or 2 then run. I counted this as a win and left it alone through the spring and early summer, just moving it around the driveway and running it from time to time. So I got more time and I wanted to tackle it again, I noticed that the truck would still struggle to start and would crank a few times more than usual then splutter to life. The FP was making all kinds of money noises so I dropped the tank and replaced the whole unit, found out it basically imploded in the tank. So I'm thinking to myself that I've fixed my problem...no. Still spluttering but running much better, so I go and do a fuel filter, plugs, check all my connections and get no real change. the only thing that changed was that the truck would start better, not like before, but better. For the past 3 years, the motor would crank MAYBE 2 times then start, it always started too fast in my opinion and I have a pile of starters with chewed-up Bendix gears to prove it. So when I started like a normal car I took notice of it pretty quick. Again I left the truck alone for the rest of the summer but this week I've been messing with it, here's what I've found.
-KOER FP 30PSI
-KOEO FP primed 35PSI
-checked FP regulator, seemed to be working correctly, no fuel smell or leaks
-After shutting off the engine the FP will creep up to 35psi then drop to zero overnight, BUT prime right back to 35 with one key cycle
-the truck will run cold fine, but as soon as it's off high idle it seems to hunt around very slightly and run rough
-code for the coolant temp sensor comes and goes intermittently
-if left to idle it will sometimes just surge up and down and die, RPMs drop low then it seems to try to catch itself
-once it comes off high idle it will surge up and down a few times then even off at the correct RPMs (doesn't always do this)
-checked IAC, working correctly
-swapped around relays
-messed with the inertia switch
-gave the harness the ol jiggle test
-drank a beer
-tried all previous steps one more time for good measure


the last piece of the puzzle is as follows. last winter when I was still driving it I had noticed that the truck would do the little surge BS on occasion but run fine afterward, seemed to come and go, but usually soon after startup. This was also coupled with the fact that sometimes it would start funny and splutter to life for a second (did this the day it died). Given that no spark condition last year and the strange idle I'm thinking ICM on the dizzy. I've gone through 2 before for other reasons but I'm still thinking that might be my culprit, or possibly the temp sensor but that doesn't explain the startup splutter. lastly, I hooked up my FP gauge to the rail and watched that when it surges and falls the FP does not drop, this leads me to believe that the surging and spluttering is not caused by a fuel issue. Ide love to hear your thoughts after reading this essay of a post.

-Jonathan

 

[RobbieD]

Open up the PCM and look at the capacitors for swelling or leaking. There's some good posts on here about this.

 

[Jazzer]

My ‘87 2.9 had many of those symptoms, showed no codes, until I replaced the O2 sensor by the y pipe. Don’t ask me to explain it, though.

-Jazzer

 

[RonD]

+1 ^^^
Check computer circuit board and the 2 or 3 cylinder type capacitors, just to take that off the table, or correct it if problems are found

ECT(engine coolant temp) sensor is only used by the computer, it tells computer when to set Choke mode, and what the IDLE should be at that temp
Colder engine needs higher idle, so wandering idle could be wandering ECT sensor, computer just has ECT temp scale and corresponding idle RPMs scale in memory
if temp is 100degF then idle is 1,000rpms
if temp is 120degF then idle is 900rpms
ect..........

ECT is a 5volt sensor, so narrow range, ECT sends back 3volts cold(65deg), and 0.6volt warm(190deg), to computer
If you have had ECT sensor codes come up then change ECT sensor AFTER looking at computer, and check ECT sensor connector/wires, any corrosion cause wandering voltage levels
ECT sensor will have TWO wires

ECT sender, for dash board temp gauge, will have 1 wire, and its a 12volt sender, so they are not interchangeable


+1 on O2 sensor, 100k miles or 12 years, is how long they last before they run out of chemicals that detect Oxygen level in exhaust
O2 is the ONLY sensor that wears out at a specific time and must be changed, other sensors "may" wear out or fail, O2 sensor WILL wear out

 

[Pix3L8]

Ok so i took your suggestions and tried a few things over the weekend. I had another o2 sensor lying around so I swapped that with no change. I also have another ECM so I poped that in and the truck ran like s**t, which is funny because I've swaped those two ECM's around before and they always ran the same. My ECT code went away which doesn't surprise me because it has done that before.

The motor runs the exact same as before, however, it didn't surge in the time it took to clean up my toolbox while it idled (10 min) so that may be something. I just shakes a little bit and I can see my shifter shaking around a bit. I had a similar problem with a subaru I had which I could never figure out. The point being it feels like a very slight misfire and I can hear the mis in the exhaust note too. Again not a dead miss but its there. I would say maybe I should adjust my valves but I would think it would run rough on high idle too if I had my lash out of spec which it doesn't and doesn't explain the weird starting. Lastly, when I did compression my #4 plug was a bit black and sooty so maybe ill investigate that more. The only thing that could be if it's just the one injector is possibly a leaking injector which may also explain why the fuel pressure drops down so fast after I shut it off. Ive only had a handful of rock auto parts fail on me and never the expensive ones so ide be surprised if one of their injectors failed this early.

if any of that sparks anyone's memory of something similar let me know, im open to ideas to try.

 

[Jazzer]

You can check the oil for a gas smell 15-20 minutes after shutting it off, and look for oil thinning.

In the dark, mist water around the plug wires to spot arcing, and separate any plug wires that touch each other.

Do you know the history of the O2 sensor you installed?

Thoughts for your consideration.

-Jazzer

 

[Jazzer]

Additional thoughts

If you have an inline spark tester, compare the spark on #4 to the others.

Inspect all, but particularly the #4 contact in the distributor cap for corrosion. Grasp the distributor rotor and check for side play in the shaft.

-Jazzer

 

[Cees Klumper]

The biggest improvements to my '90 2.9 were replacing the injectors with rebuilt Bosch ones (now around $100 delivered, it's not too difficult a job) and rerouting some vacuum lines a PO got mixed up between the throttle body and the intake manifold. These engines are very sensitive to both I have found. Good luck with the troubleshooting.

 

[rang-a-stang]

My truck had similiar issues (not the same but similiar) and it was the fuel pump under the cab. Reach under the cab while the truck is running and see if that pump is also running. if it is, check to make sure the pump in the tank is also running (even though you just replaced it). I did an EFI install on my jeep and killed 3 inline fuel pumps before I figured out there was sand in my tank and the flecks were getting into my inline fuel pump and jamming it. Maybe chunks from our old pump have gotten into your new pump?

 

[Pix3L8]

My truck had similiar issues (not the same but similiar) and it was the fuel pump under the cab. Reach under the cab while the truck is running and see if that pump is also running. if it is, check to make sure the pump in the tank is also running (even though you just replaced it). I did an EFI install on my jeep and killed 3 inline fuel pumps before I figured out there was sand in my tank and the flecks were getting into my inline fuel pump and jamming it. Maybe chunks from our old pump have gotten into your new pump?

My truck is the late model so I only have the one fuel pump, but it’s possible some crap made it’s way to the fuel injectors. It’s just such a strange problem. Sometimes it fires up perfect, other times it struggles and then died later on. No consistency. I’m still trouble shooting

 

[RonD]

Change capacitors in BOTH computers

 

[gaz]

Pix,

This should not happen with your fuel system, your quote is
"-After shutting off the engine the FP will creep up to 35psi then drop to zero overnight, BUT prime right back to 35 with one key cycle"

The fuel pressure on the rail should not bleed off, even after months, YEARS of sitting idle. I would look into THIS!

 

[Pix3L8]

Pix,

This should not happen with your fuel system, your quote is
"-After shutting off the engine the FP will creep up to 35psi then drop to zero overnight, BUT prime right back to 35 with one key cycle"

The fuel pressure on the rail should not bleed off, even after months, YEARS of sitting idle. I would look into THIS!

That symptom was present before and after I replaced my fuel pump. I did injectors last year, and a fuel filter a few weeks ago. FP regulator isn’t showing signs of failure but what else should I be looking at for a pressure loss issue? My Schrader valve has always leaked and I have a bike tire cap on it to keep it sealed….I know…..but it has literally been like this for years with no drive-ability issues. I thought maybe that is where my leak was but it still bleeds down with a FP gauge attached which would be sealing the valve….idk. Im tired of this truck but I can’t sell it until it runs right.

 

[Pix3L8]

I messed with the truck for 4 hours last night, just testing things, listening, driving it with no real luck. When I would pull codes they would change every time I did it. KOER got everything from MAP to Fuel pump issues to electrical faults etc etc etc. every time I ran the test I got different codes. KOEO gave me an 88 and a 99 which I believe is telling me the idle relearn isn’t complete. Anyway I got frustrated and really gave her the beans from the end of my driveway. Laid down a strip and cooked some tire just for fun. This prompted my CEL to come on and throw all sorts of O2 sensor errors…..which vanished just like the other codes. I got at least 15+ codes over the course of the evening none of which repeated again….if I have a fuel pressure issue there is also some sort of ground issue as well. I need to look at common grounds for the system, that is the only logical way that many codes got thrown that are not related to each other.

 

[RonD]

Reads like a computer issue

I know you swapped computer, but..................you are swapping 20+ year old computers

You can swap out a temp sender 10 times because dash temp gauge doesn't work, at some point you have to come to the conclusion the problem might just be the gauge, lol