New TBI injectors causing surging

[youcancallmedusty]

A couple weeks ago I had an issue with my ecm where the chip that controlled the injectors shorted and melted. A new ECM solved that problem, although I was still wary of the injectors so I made a plan to replace them also. I bought new Ac delco 217-2286 injectors and installed them. My 1987 gmc v2500 started up perfectly as it should but once the engine was warm (coolant temp was around 145f) it started to surge at idle. It seems like it is hunting for idle, surging anywhere from 300-800 and almost stalling out, the surges will sometimes be small and other times be one the extreme of that range, when driving there is no issues other then at complete stops where within a couple seconds of idling it will start hunting again. After hearing about the cheap Chinese injectors in the market I believed the new injectors caused it so I installed the original injectors and the surging went away. I replaced the new injectors with another set of the ac delco ones, installed them and it started surging again once it was warm. At this point I feel as if I either purchased the wrong part number or has the bad luck of receiving two sets of bad injectors which would seem improbable. I did notice slight variations between the new and original injectors but that was just with the little vent/screen on the side and the spout underneath it that has to go in the specific spot in the injector housing. The original injectors those two things line up and on the new ones they are not lined up. With the original injectors the truck does not surge at idle but which leads me away from thinking any of the sensors having issues (all are only a couple months old) or there being a vacuum leak. I read on another forum of the surging when warm could be a result of it running lean and relying on the IAC valve too much for air at idle which causes it to hunt for the proper idle, and if that’s the case then changing the base idle would help relieve the issue, but before I do that I figured I’d ask and see if anyone has any specific experience with this issue.

TLDR: new injectors cause engine to hunt/surge at idle when warm, runs as it should until coolant temp gets to 150f. Old injectors cause engine to run as it should when cold and warm.

 

[MarineOne]

Disconnect battery and touch terminals together for a few seconds it'll reset the idle air adjustment and allow computer to readjust to new injectors

 

[RanchWelder]

Yah... take off the IACV and screw it back out a few turns and try again, if MarineOne 's suggestion doesn't work.

The electronic motor on the IACV can be shot... if it got ruined from a bad ECM.

Check your grounds, everywhere... Check the IACV connector does not have a water leak or rewire it with a new pigtail.
If the ribbed rubber green Weatherpack connector gaskets get ruined, leak or removed by accident, during regular testing, they will allow water to short out the connections.

Change out your water temp sensor, as they are known to send bad signal to the ECM and cause issues.
I broke the ground wire off, where it rides the water neck, without realizing the wire was cut.
That ground is very important. It is the same wire you disconnect to set timing in open loop, where the disconnect is near the firewall...
Brown/Black Stripe...

Hopefully the ECM "Chip" is not malfunctioning... If it is, you will need to try a new one in your new ECM.

If you fry the ecm, other systems can get screwed...

 

[gmbellew]

Biggest change when the engine gets warm is that it goes into closed loop operation and starts using the O2 sensor feedback to adjust fuel. What condition is the O2 sensor in?

Strange that it only happens with new injectors. Maybe the old injectors are dirty and even though the computer is trying to make adjustment for a lazy O2, it can't bc the injectors are so dirty and won't allow the fuel to pass. With clean injectors, the lazy O2 is causing surging?

And for TBI, I always recommend ALDLDroid and a Bluetooth OBD1 cable. It allows you to see most of what the computer sees for diagnostic purposes

 

[fast 99]

What is the fuel pressure? If vacuum leak is suspected spray water on TBI, usually the base gasket will be the offender.

TBI systems primarily use MAP data for fuel trim. Then O2 for fine tuning after closed loop.

There's also a saying, don't fix it if it aint broke. Especially true today with the abundance of poor-quality parts.

It's a long shot but easy to check, what is the AC not DC voltage at battery. Should be less than .10 volt closer to .030.

 

[Copymutt]

What is the fuel pressure? If vacuum leak is suspected spray water on TBI, usually the base gasket will be the offender.

TBI systems primarily use MAP data for fuel trim. Then O2 for fine tuning after closed loop.

There's also a saying, don't fix it if it aint broke. Especially true today with the abundance of poor-quality parts.

It's a long shot but easy to check, what is the AC not DC voltage at battery. Should be less than .10 volt closer to .030.

Or, stray RF from ignition wires, Have a new Holly TB injector set up. Not installed yet. You’re making me think twice about going down the troubleshooting rabbit hole.

 

[Redfish]

You can buy a throttle body rebuild kit that includes the Orings and whatever else is required to freshen up your original injectors. It's not expensive, I picked one up from O'Reilly's.

 

[fast 99]

Or, stray RF from ignition wires, Have a new Holly TB injector set up. Not installed yet. You’re making me think twice about going down the troubleshooting rabbit hole.

Engine Masters likes the new Holley unit, but they are supposedly sponsored by them. GM TBI is simple and very dependable. May be not as fashionable as newer designs but it works.

First tried to find a 90 up standard cab 3/4- or 1-ton TBI instead of the blue truck on the left. All I found were clapped out extended cabs.

 

[youcancallmedusty]

Disconnect battery and touch terminals together for a few seconds it'll reset the idle air adjustment and allow computer to readjust to new injectors

So today after work I tried all the suggestions, starting with this one, and then resetting the iacv and relearning idle. While doing that I started the truck without the iac plugged after jumping the Aldl connector since I was curious about the base idle and how it was set. The truck would not start or run, even when warm without me touching the gas pedal. The truck is somewhat modified with a new Gm crate engine from good wrench that has a moldy bigger cam, a performer tbi intake and a stage 2 chip from Harris tuning. With that said I probably got these injectors in the summer and had the same exact experience with the old/original engine without any modifications, without knowing how to proceed or what to fix I moved on from it and reinstalled the old injectors until the other day after thinking about the new engine, ecm, and chip I figured why not try the new injectors I had to see if any of those things was the issue. With it being cold and snowy I figured I would have the time to find out why they do not work as anticipated. It just has bugged me that the old injectors work as they should but the new ones cause this idle surging issue
Today I replaced the iacv harness, reset the iac valve and relearned idle and still have the same issue, the only new thing that happened was I learned that the “base” idle seemed to be zero since the truck would not stay running without iacv installed

 

[youcancallmedusty]

What is the fuel pressure? If vacuum leak is suspected spray water on TBI, usually the base gasket will be the offender.

TBI systems primarily use MAP data for fuel trim. Then O2 for fine tuning after closed loop.

There's also a saying, don't fix it if it aint broke. Especially true today with the abundance of poor-quality parts.

It's a long shot but easy to check, what is the AC not DC voltage at battery. Should be less than .10 volt closer to .030.

O2 sensor was new this summer, it is a ac delco 3 wire heated sensor, the tps, map, Egr are also all new this summer and they are also ac delco. I just think it’s strange that the old injectors work fine and the new ones have this idle surge issue when warm

 

[youcancallmedusty]

Biggest change when the engine gets warm is that it goes into closed loop operation and starts using the O2 sensor feedback to adjust fuel. What condition is the O2 sensor in?

Strange that it only happens with new injectors. Maybe the old injectors are dirty and even though the computer is trying to make adjustment for a lazy O2, it can't bc the injectors are so dirty and won't allow the fuel to pass. With clean injectors, the lazy O2 is causing surging?

And for TBI, I always recommend ALDLDroid and a Bluetooth OBD1 cable. It allows you to see most of what the computer sees for diagnostic purposes

O2 sensor is only a couple months old and is a ac delco heated sensor, which is what I switched to when I tried to solve this problem this summer but ended up giving up and going back to the original injectors which work as they should

 

[youcancallmedusty]

You can buy a throttle body rebuild kit that includes the Orings and whatever else is required to freshen up your original injectors. It's not expensive, I picked one up from O'Reilly's.

I’ll most likely go back to the original ones if I can’t find a reason why the new ones do not work. It’s just a little issue that’s been burning in my mind for a couple months now and I figured with it being cold were I live it would be a good time to find out the cause since my work schedule slows down. I thought it would be more comfortable to solve this then to start a larger project with it being cold and snowy, I have a knack of biting off more then I can chew when it comes to working on my trucks especially if I have lots of time to think about it.

 

[MarineOne]

I should had mentioned once you reset the parameters it won't start or run unless you help it with throttle and it will hunt for idle for about 100 miles. It's just old slow computer resetting itself. BTW with the mild upgrades you did your right at limit of factory tbi anyway. I'm surprised it runs good to be honest. Maybe consider looking into sniper efi

 

[MrHorsepowerLSx]

Are the "new" injectors for a small block or the big block? Food for thought is if you purchased larger flowing injectors and had a custom chip burned for the SBC OEM flow rates that will cause drivability/idle issues

 

[fast 99]

As a test, disconnect and plug vacuum to EGR. Some EGR valves are not calibrated correctly.