1987 454 TBI down on power, runs good otherwise

beady · Aug 15, 2024

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beady · Aug 15, 2024

beady said:
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Looks kinda sketch. Broken clip, different color wires….. thoughts?

beady · Aug 15, 2024

I watched the injectors revving the throttle by hand. Passenger side looks not as good, but not god-aweful enough so the engine only makes 75 hp or so.

How do I upload videos on here? (Figured it out)

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Grit dog · Aug 16, 2024

The side with the original injector plug is spraying like chit.
The newer connector side (aftermarket so no color coded wires) looks much better.
I’d call that an issue.
And reasonable that an almost 40 year old injector could be plugged worn or faulty.
Who knows if the injector was replaced along with the connector on the other side?
Maybe the revving you hear is the downshift and it’s not slipping but just no power like your original assumption.
Slippin trans is unlikely if you say it pulls hard and shifts fine at lower % of load.

Bextreme04 · Aug 16, 2024

beady said:
I watched the injectors revving the throttle by hand. Passenger side looks not as good, but not god-aweful enough so the engine only makes 75 hp or so.

How do I upload videos on here? (Figured it out)

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when you are driving it and you say it "goes nowhere", do you mean that you hit a certain point in the throttle where the engine RPM suddenly shoots up and truck stops accelerating? Or do you mean that you hit a point where the engine RPM stays the same but the truck stops accelerating? If it is the first thing, you have a trans issue and it is slipping. If it is the second thing where it just stops accelerating but the engine RPM doesn't act like you just pushed in the clutch, you have an engine issue. If the power loss is directly related to engine RPM, then I would say the injectors being clogged is a definite possibility. The required fuel flow rate goes up much more related to RPM than it does related to throttle position. The fact you can spin the tires from idle without having the trans slip makes me think it isn't a trans issue.

Bextreme04 · Aug 16, 2024

Since you are mechanically inclined, I would buy a quality rebuild kit and fully rebuild that TBI unit. Do both the injectors and the FPR.

beady · Aug 16, 2024

Bextreme04 said:
when you are driving it and you say it "goes nowhere", do you mean that you hit a certain point in the throttle where the engine RPM suddenly shoots up and truck stops accelerating? Or do you mean that you hit a point where the engine RPM stays the same but the truck stops accelerating? If it is the first thing, you have a trans issue and it is slipping. If it is the second thing where it just stops accelerating but the engine RPM doesn't act like you just pushed in the clutch, you have an engine issue. If the power loss is directly related to engine RPM, then I would say the injectors being clogged is a definite possibility. The required fuel flow rate goes up much more related to RPM than it does related to throttle position. The fact you can spin the tires from idle without having the trans slip makes me think it isn't a trans issue.

I’ll try to get a video driving it. It pretty much just peters out and stops accelerating (if you have it in 1 manually, or top gear and are accelerating gently on the gas pedal). As you keep pressing the gas more (in D and at highway speed), it kicks down happily and readily, but there is zero power to accelerate. You can’t accelerate again until you back off the throttle and upshifts. Eventually you’re going as fast as it will go and balancing the throttle btwn holding that speed, or downshifting and having higher (but not spiking) engine revs, but no forward pull.

It reminds me of my old YJ carb’d wrangler with 117 hp new, or the old 1985 Rx-7 I had with a 3-spd auto and 100 hp. You’re fighting for every mph of acceleration and swear when someone forces you to lose a few mph (at highway speed) because it’s a struggle to gain them back again.

It was far worse with a trailer, would struggle to keep 55-60 mph without adding enough pedal travel to cause it to kick down, and once it kicks down and revs rise there seems to be the same, or really a bit less, power.

And the lack of exhaust volume/sound at higher rpm seems to suggest it’s not making much power to me also.

Bextreme04 · Aug 16, 2024

beady said:
I’ll try to get a video driving it. It pretty much just peters out and stops accelerating (if you have it in 1 manually, or top gear and are accelerating gently on the gas pedal). As you keep pressing the gas more (in D and at highway speed), it kicks down happily and readily, but there is zero power to accelerate. You can’t accelerate again until you back off the throttle and upshifts. Eventually you’re going as fast as it will go and balancing the throttle btwn holding that speed, or downshifting and having higher (but not spiking) engine revs, but no forward pull.

It reminds me of my old YJ carb’d wrangler with 117 hp new, or the old 1985 Rx-7 I had with a 3-spd auto and 100 hp. You’re fighting for every mph of acceleration and swear when someone forces you to lose a few mph (at highway speed) because it’s a struggle to gain them back again.

It was far worse with a trailer, would struggle to keep 55-60 mph without adding enough pedal travel to cause it to kick down, and once it kicks down and revs rise there seems to be the same, or really a bit less, power.

And the lack of exhaust volume/sound at higher rpm seems to suggest it’s not making much power to me also.

Yeah, that's not a trans issue. 100% sounds like you are running out of fuel or the throttle isn't opening all the way. I would definitely start by getting yourself a quality rebuild kit and rebuild that whole TBI including both injectors and the regulator. Then I would make sure that the throttle is actually opening the entire way with full pedal press and verify the voltage output on the TPS matches those positions. I believe it needs to be ~0.5v at closed throttle and ~4.5v at WOT. Then go get it nice and warm and verify the base timing is correct. I bet the combination of all that fixes your issue.

Other things to do/check would be to pull all the spark plugs and run a compression test and inspect the plugs. I would then install all new plugs(AC Delco CR43TS) with verified gaps.

Snoots · Aug 16, 2024

If you have the stock exhaust manifolds, check the passenger side for a valve. It could be frozen.

beady · Aug 17, 2024

Some videos, hopefully you can hear it. I couldn’t find anywhere within an hour drive with new (non rebuilt) injectors. Anyone have suggestions on a good place to order injectors/rebuild kit from?

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JBswth · Aug 30, 2024

beady said:
So I bought this 1987 R20 a couple weeks ago, and it seems to run well except it’s down on power as rpms rise. Pulls pretty strongly from a stop, but as revs rise it stops making power. And if you are driving and cause it to downshift, it immediately does nothing. Makes noise and seems to rev, but no power. Won’t accelerate unless you let off the gas and ease into it. Then it will run at 70+ fine, until you dip into the gas too much, and again, nothing. We pulled a horse trailer and it was a chore to keep speed up without it downshifting and going nowhere.

I checked fuel pressure and it’s 12+ psig.

Tried checking timing, but not sure what I’m looking at. Seems like the mark is to the passenger side (to your left when standing in front of truck) of the tow of fixed toothed timing marks on the engine? That’s with the timing wire pulled.

Oh yeah, it drives exactly the same with the timing wire connected or not.

Also, there doesn’t seem to be a check engine light to pull codes. The spot in the bottom of the speedometer is there, I can feel it with my finger, but no bulb. And o don’t feel it dangling around back there either. Is there a way to hook a bulb or meter to sone of the ALDL pins and read flashes that way? Or some reader I can buy or make (made one for my old Benz)?

Thanks for any insight.

Sounds like the trans is slipping. Does the vehicle speed increase with rising RPM with a feeling of no guts? If so, it might be running too lean. If the vehicle does NOT speed up with increasing RPM, its the trans.

J. B.

beady · Aug 30, 2024

JBswth said:
Sounds like the trans is slipping. Does the vehicle speed increase with rising RPM with a feeling of no guts? If so, it might be running too lean. If the vehicle does NOT speed up with increasing RPM, its the trans.

J. B.

It will speed up with engine speed, but it feels like it only has 100 hp. Slow to accelerate, and if it kicks down it just won’t accelerate until you let up and let it upshift and give it gentle gas.

I posted sone videos of the injectors in this thread and you can see one side looks poor, so it could be running out of fuel and leaning out.

beady · Sep 2, 2024

So following up on the solution. The thermostatically controlled flapper on the air filter housing didn’t have the hose running down to the shroud on the exhaust manifold to supply heat and open the flapper. So the engine was choked for air. I wedged a rag to hold the flapper open and it runs 100% better. Trans shifts fine.

I’m going to look at aftermarket air filter housings without the snorkel/flapper I think.

Also, I’m going to go ahead and rebuild the tbi/regulator/replace injectors since I bought the parts already.

1987 454 TBI down on power, runs good otherwise

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