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Old 07-23-2021, 04:25 PM   #1
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1990 454 tbi mh too lean I think

I have a 1990 454 tbi. Was running a little rough and idling high so I replaced plugs, wires, cap, rotor. Changed nothing. Then I replaced the engine coolant temp sensor and it purred like a kitten. Put it in gear and it wants to die. Idle is too low. Tried driving it and it has absolutely no power. I would be lucky to get it to 30 mph. With the breather off revving it it sounds like it is starving for fuel. Please help!
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Old 07-23-2021, 09:51 PM   #2
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Welcome to IRV2... check your fuel pressure.. Chevy puts same eng and trans in pickup trucks as they do rv.. so go to big box a/p store and get a 1990's Chevy pickup repair book ie. 1990 Chevy c2500 or even c1500 with 454 and you will find it a great resource.. same eng and trans.. fuel pressure willbe listed.. and trouble shooting guide.. tune up stuff .. also pick up G,M, obd1 code reader.. they are cheap, if you have obd1, you may not.. look to see if you have cats.. they could be melted and plugged up.. most likely fuel pressure.. if rv has been ran lean for a while.. they will melt inside of cats.. if you have the old style.. easy check just bypass or do exhaust back pressure test.. good luck and let us know what you did and maybe better members then me will help you just off top of my head fuel pressure should be 40psi somewhere around that.. oh have you changed fuel filler..? The 90's 454 we had was a screamer..we could run 90 all day long fully loaded..
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Old 07-23-2021, 11:13 PM   #3
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It is quite possible that you got a bad (or mis calibrated) sensor out of the box. This is especially true with aftermarket low cost sensors.

If you still have the old sensor, put it back in and check to see if the RV get back up to speed as before. Then you can restart the diagnostics.

You could have other drivability issues, such as a vacuum leak, low fuel pressure, clogged fuel filter, miscalibrated TPS (throttle position sensor).

Later on you may want to get a AC Delco 1551107 CTS (coolant temp. sender).

Lastly, Harris Tuning has a great trouble shooting page on their web site. Very informative. It will help you diagnos the problem, verses spending hours and dollars getting no where.

https://harristuning.com/Tbi/troubleshooting/

Good Luck. Let us know what you find.
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Old 07-23-2021, 11:34 PM   #4
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Well I pulled the air breather to start messing with stuff and realized the connector on one of the injectors was off. I must have caught it with the breather when I was putting it back on. Engine runs great and has at least as much power as before. Will update if anything changes. Thanks for the replies. Feel like an idiot but at least it was easy.
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Old 07-24-2021, 10:30 AM   #5
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Great.. been there many times.. and will undoubtedly will again..
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Old 07-24-2021, 10:50 PM   #6
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Glad you found the wire connector off of the one injector. Also glad you gave us an update.
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Old 07-25-2021, 06:46 AM   #7
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Quote:
Originally Posted by Repoman707 View Post
I have a 1990 454 tbi. Was running a little rough and idling high so I replaced plugs, wires, cap, rotor. Changed nothing. Then I replaced the engine coolant temp sensor and it purred like a kitten. Put it in gear and it wants to die. Idle is too low. Tried driving it and it has absolutely no power. I would be lucky to get it to 30 mph. With the breather off revving it it sounds like it is starving for fuel. Please help!

Glad to hear that you quickly figured this out and that it was an easy fix!

I also have recently purchased a 1990 RV wit the 454 engine in it. It really has some power! However, mine has a carburetor on the engine.

My question to you is what kind of gas milage are you getting? I'm considering switching over to TBI to help my milage.
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Old 07-25-2021, 07:38 AM   #8
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My 93 with the banks exhaust and intake gets around 8 mpg. Changing to TBI alone will be a bit of work and I don't know if you will get much improvement in power or mileage .
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Old 07-25-2021, 10:31 PM   #9
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Glad to hear that you quickly figured this out and that it was an easy fix!

I also have recently purchased a 1990 RV wit the 454 engine in it. It really has some power! However, mine has a carburetor on the engine.

My question to you is what kind of gas milage are you getting? I'm considering switching over to TBI to help my milage.
Iím getting about 8 mpg. I would not try to switch to the tbi. Too many sensors and things that go wrong. I am seriously considering switching mine to a 4 barrel carb.
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Old 07-25-2021, 11:37 PM   #10
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1994 28ft Southwind Storm 454 TBI w/4L80E keeping it at a reasonable speed (not more than 60mph) will yield best MPGs in the 8 mpg range on the flats with no head/side winds.

Strictly city driving...6-7mpg

Highway with hills/grade/s...in the 7 mpg range
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Old 07-27-2021, 01:53 AM   #11
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Glad to hear that you quickly figured this out and that it was an easy fix!

I also have recently purchased a 1990 RV wit the 454 engine in it. It really has some power! However, mine has a carburetor on the engine.

My question to you is what kind of gas milage are you getting? I'm considering switching over to TBI to help my milage.
How certain are you you have a carb vs TBI?


You'd be surprised how many could not tell the difference.
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Old 07-28-2021, 05:40 AM   #12
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How certain are you you have a carb vs TBI?


You'd be surprised how many could not tell the difference.


Does a TBI have a choke plate? LOL

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Old 07-28-2021, 01:37 PM   #13
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Quote:
Originally Posted by RVforTwo View Post
I also have recently purchased a 1990 RV with the 454 engine in it. It really has some power! However, mine has a carburetor on the engine.

My question to you is what kind of gas milage are you getting? I'm considering switching over to TBI to help my milage.
TBI would have come originally on your 1990 Chevy 454. TBI was introduced in 1988 on the 454. Now, it is entirely possible a previous owner removed the TBI and intake manifold, and installed a carburetor. Hear about people doing this all the time. Often the engine begins to run rough, stalls, misfires, and the TBI system is blamed.

Honestly, the TBI systems is very rudimentary. There are only a few sensors. Throttle Position, O2 and Water Temp. Add to that the Ignition Module (which tells the computer what rpm the engine is doing) and Idle Air Motor and a simple fuel pressure regulator. Very simple.

Due to its simplicity, rarely does anything go wrong. The fuel pump in the gas tank is far more likely to strand you than anything else.

TBI being simple, also chokes down the 454, and these short comings were addressed in 1996 with the Vortec family of engines. GM changed to Vortec heads, and tune port injection. Still a very simple system, but with more power.

Note: Banks used to offer a power pack kit for the TBI system which increased the power significantly.

Luckily our rig has the Banks system on it, and we get between 8 and 9.5 MPG if I keep my foot out of it. On our last trip, I kept going over 70 mph, and we got an average of 8.8 MPG over 2200 miles.
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Old 07-28-2021, 11:25 PM   #14
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Forgot the MAP sensor...


Fuel control is based off the MAP and ICM. MAP measures the vacuum (load) and sends it's info to the PCM. The ICM sends RPM info. The computer then looks at a preprogrammed table and sprays fuel amount based on vacuum/RPM reading. O2 sensor/s trim fuel ratio after burn.
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