94 2.3L w/ 17# injectors - Intermittent Rough Idle

wizkid00104 · Sep 13, 2016

So this past weekend I replaced my stock injectors with 17# ones. The truck has 223k on it. At the same time, I replaced my spark plugs and wires. I already checked and the wires are correct.

The truck runs good, but my vacuum was down after the replacement. It usually idled at 19 inHg and now it is closer to 15 inHg. It idles really rough and will occasionally stall. I figured it has to be a vacuum leak since it worked fine when i disassembled it.

I replaced all vacuum connectors and tubes that were dry rotted. I replaced the upper manifold gasket and torqued the bolts to 22 ftlb. I replaced the EGR gasket tonight because I thought that was problem.

After driving it, it idles smoothly for ~45 seconds then the vac drops to 15 inHg and starts running really rough again. Its like something in the computer is adjusting the way the engine runs after it sits idle for a bit. There is NO CHECK ENGINE LIGHT on.

It is a 94 2.3L 5 speed, no A/C, Jet Performance Module (installed 5+ years ago), and MSD ignition coil for the exhaust side plugs. It has a Magnaflow repalcement cat and a 2.25" Cherry Bomb exhaust. O2 sensor was replaced last fall.

I am thinking... Reset the computer and remove the Jet module, snug up EGR bolts, and then get a vacuum pump and start checking components for leaks. I am just stumped because it worked before and not after.

Here is the link to the post in my build thread: http://www.therangerstation.com/forums/showpost.php?p=1574659&postcount=505

Please provide thoughts!!!!! I am running out of ideas..... :icon_confused:

wizkid00104 · Sep 13, 2016

I also thought about get another MAF and boring the measurement hole to match the new injectors.

Mark_88 · Sep 13, 2016

Sounds like your computer is sensing the extra fuel and trying to cut it back...or you could be correct about the vacuum leak and it has evaded you so far.

With this model year not sure if you could put a scanner on and get real time data to see if the computer is trimming the fuel supply...I have a link that might help...ooops...link is no longer valid...

Since you have a vacuum gauge there is a list at the bottom of this one that might help...

http://www.gregsengine.com/using-a-vacuum-gauge.html

alwaysFlOoReD · Sep 13, 2016

I agree with Mark re; injectors too big now. If the rest of the motor is stock then, IMO, the injectors are the problem.

wizkid00104 · Sep 13, 2016

I understand they are bigger, but I would think that would cause a constant problem of idle, it's the intermittences that confuses me now. And I only increased the size of the injectors because others did it successfully, even going to 19#.

Sent from my iPhone

wizkid00104 · Sep 13, 2016

That was a really good article mark, thank you.

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alwaysFlOoReD · Sep 13, 2016

Do you still have the old ones?

wizkid00104 · Sep 13, 2016

Yes. They could stand to be cleaned. I presume the suggestion is to swap them back in to see if the problem goes away?

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MrGiggles · Sep 13, 2016

Spray the injectors down with brake cleaner, if the idle changes, they are leaking vacuum. Do the same to any areas that could have a leak.

The PCM will adjust for the bigger injectors within a specified range, if it has to adjust past that threshold, an A/F mixture rich code should set. If you don't have a code, that's not likely the issue. You are on the right track looking for vacuum leaks, something must have been disturbed during the swap.

Mark_88 · Sep 13, 2016

You're welcome...hope it gave you some ideas.

I did a bit of reading on this and found quite a bit that says to go back to stock injectors if you have problems...the solutions to resolve and allow you to use the bigger injectors can be expensive...

The trick is that when we increase fuel we also need to increase the air intake so the air fuel mixture remains the same 14.7:1 (I think that's the number).

To increase air flow you need to either adjust the valve duration, put in bigger valves, or go with forced induction...tuning the chip might help some...but it might cost you a small fortune if you are not careful.

This is not a huge jump in size...but enough to cause problems...but there is always a consequence in these things.

If you can program the chip to modify the fuel flow that might help...but I have no idea where to start on that subject...here is a link that might help...more reading but some good information there...even if it is a Jeep site...

http://www.wranglerforum.com/f210/jet-chips-help-214439.html

alwaysFlOoReD · Sep 13, 2016

Slightly off topic, I'm doing an engine swap for a bud. He has a 78 f150 with a 400. He cooked both the tranny and motor. When I took out the 400 I found the wire for the oil pressure sending unit pinched under the intake. The engine had just recently had an intake and carb swap. I never heard the engine run previous but I bet there was a vacuum leak. I'm not saying you did the same but it is worth checking around with mirror and flashlight. And propane works too for finding leaks.

Sent from my XT1032 using Tapatalk

wizkid00104 · Sep 14, 2016

MrGiggles said:
Spray the injectors down with brake cleaner, if the idle changes, they are leaking vacuum. Do the same to any areas that could have a leak.

The PCM will adjust for the bigger injectors within a specified range, if it has to adjust past that threshold, an A/F mixture rich code should set. If you don't have a code, that's not likely the issue. You are on the right track looking for vacuum leaks, something must have been disturbed during the swap.

This may be a dumb question, but what does the brake cleaner do? Get sucked in an combusted? Is that how you hear a difference?

wizkid00104 · Sep 14, 2016

alwaysFlOoReD said:
Slightly off topic, I'm doing an engine swap for a bud. He has a 78 f150 with a 400. He cooked both the tranny and motor. When I took out the 400 I found the wire for the oil pressure sending unit pinched under the intake. The engine had just recently had an intake and carb swap. I never heard the engine run previous but I bet there was a vacuum leak. I'm not saying you did the same but it is worth checking around with mirror and flashlight. And propane works too for finding leaks.

Sent from my XT1032 using Tapatalk

Hmmm.... also a good suggestion. Sounds like I will be taking it back apart one way or another. Thanks!

wizkid00104 · Sep 14, 2016

Ok. I got a vacuum pump and did some testing. Fuel pressure regulator held 20inHg for 5 minutes as did the brake booster. The solenoid for the EGR did not the (EVR). I tested remove it from the truck and connected it to 12V to it and it popped the fuse. Resistance is reading 0.6 ohms through the coil, so the valve is definitely shot. It should be between 20-70 ohms. This would certainly seem to be where my leak is coming from if the valve is bad. I need to check the electrical and see if a fuse blew as well.

wizkid00104 · Sep 14, 2016

Here is the reference I used: http://www.ford-trucks.com/forums/115928-egr-vacuum-regulator-evr.html

I see the valve is powered from the PCM. I hope the outputs are current limited to avoid ruining the PCM when a short like this occurs.

94 2.3L w/ 17# injectors - Intermittent Rough Idle

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