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Old 09-29-2016, 04:09 AM   #1
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1984 27' Airstream 270
Scotia , New York
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Any MH motorheads out there?

When I bought my 84 Excella 270, it came with the stock 7.4L motor with a Quadrajet carburetor. Mileage was about 7MPG and I wanted to get better MPG and eliminate the endless cranking waiting for fuel to get to the engine.
A few years ago I installed a TBI kit from AFI and with some difficulty, I got it installed and working OK and the install is documented here:
http://theouterlimits.ws/projects/ai...de_Page01.html
My gas mileage did not improve much, maybe .5 to 1 MPG intermittently.

On my last wander of about 300 miles I tried 93 octane in the tank, I had 10 gallons of regular (87 octane) and added 20 gal of 93 and at mid trip I added another 15 gal of 89. So overall the octane on the trip was higher than regular grade. The end result was about 8.5 MPG and that was loaded medium heavy with an extra ton of trailer in tow.

A friend mentioned that I may get better mileage with regular if I had a knock sensor for my ECM. The designer of this kit claims a knock sensor is not needed and usually causes more problems than it solves, so it was not included. With the 6 to 7 ton load and long stretches of hills our vehicles endure, I wonder who is right?

Anyone out there with experience with knock sensors on MH engines, or any other solutions to better mileage?
(Skipping Banks headers, they are beyond my budget)
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Old 09-30-2016, 12:06 PM   #2
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1974 20' Argosy 20
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Wayne, as I was assembling the parts to build a TBI kit for my 454 it was recommended to me that I install a knock sensor for the reasons you described.

However I didn't install one because my block had no provisions for one. My TBI harness has the connector for the knock sensor but the guy doing my programmING disable the sensor for me. If I ever figure out a way to install a knock sensor I'll do so.

Did the EFI kit come with a connector for the knock sensor? If not I can put you in touch with someone that should be able to sell you the parts needed to add it to you harness and he could probably do the programming as well.

Brad
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Old 10-02-2016, 09:46 AM   #3
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1991 25' Airstream 250
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I don't think a knock sensor will have any negative impact on gas mileage, unless you have an underlying problem with your Motor. In fact, possibly the opposite. It retards the timing if it senses a knock in your engine (hence tries to protect it) or if the voltage it reads is outside the Chevy parameters.

For further information, refer to the Chevy "Driveability Symptoms,” Section "2,” for "PCM/ECM Intermittent Codes or Performance.” They are available online.

I know a bit about knock sensors.....as Brad and Martin will testify. In fact, they know quite a bit too, from trying to help me out. Chevytalk forums is also your friend. This is from the Checy manual and relates to Motors with the 4L80E. It has a seperate section for those without.

Chevy emissions manual notes on knock sensor/fault code 43

This system uses a knock sensor in connection with the ECM/PCM to control spark timing to allow the engine to have maximum spark advance without spark knock. This improves driveability and fuel economy and is used on all engines except the 2.5L.

On vehicles equipped with the 4L80-E transmission, a Powertrain Control Module (PCM) is used. The PCM has an integrated ESC module, so on this system there are only three components. Those components are the knock sensor, powertrain control module, and the wire inbetween.

A 5 volt reference is applied to the knock sensor which has an internal resistance of about 3500 ohms. This resistance will lower the applied voltage to about half or 2.5 volts.

When a knock is present, a small AC voltage is produced by the knock sensor and transmitted to the PCM riding on top of the already existing 2.5 volts. An AC voltage monitor inside the PCM will detect the knock and trigger the PCM to start retarding the spark incrementally.

Two separate diagnostic checks are performed by the PCM. The first check merely monitors the voltage on the ESC circuit and if the voltage is below about .04 or over about 4.6 volts, Code 43 will be set.

The second check, is a system performance check. During the course of operation, the PCM will begin advancing the timing in increments while anticipating a knock signal. If no knock signal appears after the self check has been performed twice,

Code 43 will be set.

ELECTRONIC SPARK CONTROL (ESC)

Code 43 sets if there is an open or short to ground in the ESC circuit.
If the conditions for a Code 43 are present, the "Scan” will always display "YES.” There should not be a knock at idle unless an internal engine problem, or a system problem exists.

Code 43 sets - Signal to the ECM/PCM has remained low for too long or the system has failed a functional check.

Code 43 means that either voltage on CKT 496 is too high or too low or that the ESC system has failed the self check at least twice.

Vehicles with a V6 or V8 cylinder engine have an ECM (referred to as GMCM) with three parts for service. A controller (an ECM without a PROM), a PROM with specific program information for an engine and vehicle and a CAL-PAK with specific calibration information.

Vehicles with the Hydramatic 4L80-E transmission have a Powertain Control Module (PCM) or GMP6 which use a Memory and Calibration unit (MEM-CAL)

It interacts with the ECM/PROM.
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Old 10-03-2016, 03:36 PM   #4
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1984 27' Airstream 270
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Quote:
Originally Posted by bkahler View Post
Wayne, as I was assembling the parts to build a TBI kit for my 454 it was recommended to me that I install a knock sensor for the reasons you described.

However I didn't install one because my block had no provisions for one. My TBI harness has the connector for the knock sensor but the guy doing my programmING disable the sensor for me. If I ever figure out a way to install a knock sensor I'll do so.

Did the EFI kit come with a connector for the knock sensor? If not I can put you in touch with someone that should be able to sell you the parts needed to add it to you harness and he could probably do the programming as well.

Brad
Thanks Brad, & Boom Sounds. I may make an attempt to find the parts to add the knock sensor & Spark Control Module (and wiring) I did find a threaded hole in front of the starter motor and I believe that is where it should go. I noticed some setups use a sensor on each side but I am not sure if it is for my setup. My kit is designed around a 1990 Chevy truck TBI system and did not come with any knock sensor wiring.
I still have the stock 1984 Transmission so there is no complication with that interface.

Besides acquiring the parts and wiring I will have to have Affordable Fuel Injection program a PROM that uses the knock sensor. Unless AFI can supply it, I may look in a salvage yard for a harness and the Spark Control Module.
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Old 10-04-2016, 07:17 AM   #5
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I have a 1991 and the knock goes straight into the block. Coolant leaks out if I remove it. You're right that it's just above the starter. I can send pics if it helps.


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Old 10-05-2016, 03:34 AM   #6
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1984 27' Airstream 270
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Quote:
Originally Posted by Boom Sounds View Post
I have a 1991 and the knock goes straight into the block. Coolant leaks out if I remove it. You're right that it's just above the starter. I can send pics if it helps.


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No need for you to climb under yours, I looked at my motor yesterday and it has a fine threaded hole about like this:

I have read that some engine blocks use the same threaded hole as a coolant drain. It does not look that way in mine. The service records show that the engine was swapped out in 1990, so the block may not be the same as the original 1993 P30 chassis.
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Old 10-05-2016, 03:19 PM   #7
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Be aware that there are a couple of different versions of the knock sensor for the 1991 version; they have different omhage. AC Delco sold me the wrong part, despite it being derived from my VIN. Net result was a very long winded and expensive fault finding process as to why I kept getting a fault code being thrown up.


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