Fuel delivery problems on 1990 LY MH

smily · 04-07-2004, 07:12 AM

Okay, I am having fuel delivery problems with my 1990 LANDYACHT MH.

I have searched the forum and there is plenty of info on the classics, pre-1990.
Some of it was very beneficial like, I did not know there is a fuel filter at the carbuerator. I will look for one today on mine.

A little background info:

1990 LY MH
P-30 Chevrolet Chassis
454 gasoline
Fuel Injected, (throttle body)

I ran the tank pretty low trip before last trip out, almost empty. Since then, I fueled up and drove 150 mile round trip with no problems this past weekend. Now I am getting ready for road trip this weekend. I am having fuel delivery problems now.

Engine starts well, idles well. When I rev engine or demand more fuel, I can see the injectors intermittently spray. Spray looks good but intermittent.
Engine of course revs in corrulation to injectors, up and down quickly.

Suspect, running low on fuel trip before last has caused me to pick up trash off of bottom of gas tank. Replace Inline fuel filter on frame rail left side of chassis. Runs good for about 5 minutes but returns to intermittent revving.
I could definitely tell the difference in the new fuel filter and the old, (one on frame rail). Also, I did see some varnish in the fuel. I pull filter again and check to see if Electric fuel pump is delivering. My fuel only pumps if engine is turning over, not upon key to first or accessory position. I think this is due to oil pressure protection feature. (experience with blown fuses tells me this, I had a shorted oil pressure sending unit wire and it was blowing the fuse to fuel pump, repaired on maiden voyage, see "landyacht has landed"). While fuel is pumping onto ground at filter location, I see more varnish than I care to see. maybe not varnish but definitely a brownish color, Rust maybe?

I have searched all over for the electric fuel pump, I cannot find it anywhere. My frame rail is very obstructed behind the rear axle and tag axle. I can see the fuel lines to the point that they change from hard metal lines to rubber hoses. I cannot see them above the fuel tank.

Does any one know where the Fuel Pump is on the MH?

Smily

TomW · 04-07-2004, 08:51 AM

Quote:

Originally Posted by smily

Does any one know where the Fuel Pump is on the MH?

There is an excellent chance that it is inside the fuel tank being kept cool by the fuel itself. From what I have heard, that's one reason fuel gauges will read "E" when there is still ten gallons of fuel left - the manufacturer wants to make sure there is always enough fuel left to keep the pump cool.

If this is your case, and you have a lot of miles on the unit, running the tank too low may have overheated an old pump, and pushed it over the edge

thenewkid64 · 04-07-2004, 05:39 PM

Ken,

One other option to get you "on the road" is to pull the line off the engine mounted pump and shoot air pressure back through the hose. This should at least knock the crud off the pickup sock that is likely clogged. It will not solve the problem of the sock and associated debris. the only way to fix that is to drop the tank.

smily · 04-07-2004, 08:06 PM

Okay after rubbing a lot of PFM on the throttle body and other associated fuel intake items, it is working again.
I was convinced that it is not a fuel pump issue. Book says, "should be able to fill a pint container in 15 seconds" Shoot, I could fill a half gallon in fifteen seconds.

I do not have a mechanical pump on the engine, only one pump in the tank.
I poked a prodded all oxygen sensors, took apart throttle body and injectors, jiggled wires and now it is working

I dont know what did it but, it is fine now. I wish I did know so I can repeat the miracle if needed.

Smily

jim8860 · 04-07-2004, 08:27 PM

Some times the fuel pressure regulator get sticky from sitting. Mine acts up from time to time. One of my GM techies tell me it just time before the fuel pump crap out. Well, I will just just keep my eye on it.Good Luck

smily · 04-14-2004, 06:10 AM

Okay, did some poking around last night.
Changed O2 sensor and ran for awhile.

After about ten minutes, motor cut off. acted starved for fuel again, I think.

So I start looking at TBI and Vacuum hoses I notice this thing on the right side of motor. This thing has a vacuum line that comes straight off of TBI. It also has a cable assembly plugged into it with three conductors. I pull vacuum line and it has a lot of vaccum and motor idels down slightly.

As I put vacuum line back on I notice that cable connector is not seated completely. I wiggle try to seat the connection but it is tight. As I seat the connection, the engine idles up.

So I wiggle the connector a little and it acts just like problem I was having before. But now I can induce problem at will by moving connector around.
Ah Ha!

It is strange, if I remove connector entirely from module, the motor still runs but idles low. if I press connector in it runs good and idles up. If I wiggle wires as though weak (intermittent) contact, it almost cuts the motor off.

I suspect that this connector was not seated entirley and was intermittently making contact, causing hesitation in motor.

I have looked at manual but I cannot figure out what function this module provides.

Any takers?

Here are a few photos

74Argosy24MH · 04-14-2004, 06:16 AM

MAP (manifold absolute pressure) sensor, it tells the ecm how much vacuum in the manifold. Could be bad, bad connection. Did you ever check for set codes?

John

TomW · 04-14-2004, 06:20 AM

Quote:

Originally Posted by 74Argosy24MH

MAP (manifold absolute pressure) sensor...

I'll "second" that.

smily · 04-14-2004, 06:21 AM

I did some home work yesterday at sites provided and got a little overwhelmed by it.

But if some one holds my hand, maybe I will give it a shot.

I am hoping to get it to some one who is well versed in diagnostics and codes.

can you explain codes?

Smily

smily · 04-14-2004, 06:26 AM

I read how to get codes to flash, but how will I know what it is telling beyond the digits or numbers as in 1 flash and 3 flashes = 13 ?

What does each code mean

e.g. 12, 13, 14 etc....
Smily

74Argosy24MH · 04-14-2004, 06:40 AM

All the sensors should send a voltage to the ecm. If they are in the proper range everything runs fine. When they go above or below then the ecm records a code and you can read these to tell what sensor is bad (disconnected, broken wire; it is sort of open in that respect; the ecm just knows the voltage is outside the range).

Below is a picture of the ALDL connector as it would be mounted from the factory. Because these are just chassis when they go to Airstream they are bundled with the dash wiring and AS mounts them where they want. My HR is vertical and on the firewall, wire length won't let them go very far from the fuse block. Everyone I have seen is black and looks exactly the same.

A and B are the terminals you want to short. If you can't determine which are A and B because of orientation, check the end terminals for ground with a VOM, the one next to it is B.

I scanned the OBD1 codes yesterday but did not get a chance to post. I will do it later today and put a link in this thread.

John

smily · 04-14-2004, 06:47 AM

Just got done Google searching codes and I see that most GM products have the same codes.

I have a few list of codes printed out.

I will give it a shot today.

Maybe I can list the codes here

here is a link just in case:

http://www.griffinproductions.com.au/diags/errors.htm

ECM Diagnostic Codes

CODE

Circuit Affected

12 No Distributor (TACH)
13 O2 Sensor Not Ready
14 Shorted Coolant Sensor Circuit
15 Open Coolant Sensor Circuit
16 Generator Volatage Out Of Range
18 Open Crank Signal Circuit
19 Shorted Fuel Pump Circuit
20 Open Fuel Pump Circuit
21 Shorted Throttle Position Sensor Circuit
22 Open Throttle Position Sensor Circuit
23 EST/Bypass Circuit Problem
24 Speed Sensor Circuit Problem
26 Shorted Throttle Switch Circuit
27 Open Throttle Switch Circuit
28 Open Fourth Gear Circuit
29 Shorted Fourth Gear Circuit
31 Shorted MAP Sensor Circuit
32 Open MAP Sensor Circuit
33 MAP/BARO Sensor Correlation
34 MAP Signal Too High
35 Shorted BARO Sensor Circuit
36 Open BARO Sensor Circuit
37 Shorted MAT Sensor Circuit
38 Open MAT Sensor Circuit
39 TCC Engagement Problem
44 Lean Exhaust
45 Rich Exhaust
51 PROM Error Indicator
52 ECM Memory Reset Indicator
53 Distributor Signal Interrupt
60 Transmission Not In Drive
63 Car And Set SpeedTolerance Exceeded
64 CarAccelerationExceedsMaximumLimit
65 Coolant Temperature Exceeds Maximum Limit
66 Engine RPM Exceeds Maximum Limit
67 Shorted Set Or Resume Circuit
.7. 0System Ready For Further Tests
.7.1 Cruise Control Brake Circuit Test
.7.2 Throttle Switch Circuit Test
.7.3 Drive (ADL) Circuit Test
.7.4 Reverse Circuit Test30ISC Circuit Problem
.7.5 Cruise On/Off Circuit Test
.7.6 "Set/Coast" Circuit Test
.7.7 "Resume/Accelleration" Circuit Test
.7.8 "Instant/Average" Circuit Test
.7.9 "Reset" Circuit Test
.8.0 A/C Clutch Circuit Test
1.8.8 Display Check
.9.0 System Ready To Display Engine Data
.9.5 System Ready for Output Cycling Or In Fixed Spark Mode
.9.6Output Cycling.0.0All Diagnostics Complete

59toaster · 04-14-2004, 07:44 AM

Yeah it seems overwhelming but take the thing in small sections and relate it to the functions of the carb and it's not so bad.

Map, O2 are ignored from cold start. At that point the ECM is running "open Loop" on a preset fuel curve that is tied into the coolant temp. Once the engine gets to about 160degrees it will start sampling the O2 sensor to see if it's give a percived correct temp and is hot enough to use. By 170degrees it should have gone closed loop and base all it's mixture off of the MAP sensor and the O2.

One big mistake that at people make is to drop a 160-180 Thermostats in these. What will happen is the engine will drop low enough temp to go back to "open Loop" sometimes So if they go back open then they wil start dumping fuel and foul out plugs and get porr echonomy. These systems are calibrated to run a 195 degree thermostat to prevent it from going open loop once warm. Normal operating temp is 210 degrees on all GM FI vehicles. It can be overridden with a new chip.

THe MAP is a pretty hardy component that doesn't fail often at all. Most problems that will trip a MAP light are vacuum or wiring problems as your wiggling is confirming. I have pestered the GM wrench at the dealer accoss the street from work and they almost never have to replace a MAP. they don't even stock them because it is such a rare occurance that they fail.

I have a factory service manual for 88 454 FI. It's will not be exactly correct but the diagnostic checks should work. Let me know what you want to check and I'll get the info for you. Book is at home so it will be tonight before I can help.

That ADSL software, adaptor and the laptop are sweet if you want to try it. My buddy has it and I am very impressed. I just have not bought a laptop yet so I can use it. The system can be diagonosed with a test light, VOM and knowledge so it's not imparative to have the computer. It just makes it a little easier to find intermitant faults. Should not hamper you with the problem your.

I chased all sorts of problems with my 88 and EVERY problem was Vacuum related. Go over those vacuum lines with a fine tooth comb. Take some carb cleaner and spray around the base of the TPI. That gasket is very prone to failing.

EGR is also something that will not be active till the ECM goes Closed loop. The symptoms of it sticking open intermitantly would be runs fine cold. Will run fine till driven and RPM sustained over 1200 longenough for ECM to activat EGR. Then once it goes back to idle it will be stumbling and possibly stall.

The EGR contol solonide (if yours is the same as mine) seem to gum up and stick with age. Trace the vac line from the EGR back to the box that is about 4 inches long 1.5 x1.5 two vac lines and a 2 or 3 wire connection (three wre is feed bac version). On mine it's sitting right behind the alternator bracket on the intake. That solonoide would stick open and alow the EGR to be active at idle. Once the engien was shut off and vac source removed it would close and my run problem would be gone till it got activated again. Couple drops of air tool oil into the ports solved it.

smily · 04-14-2004, 08:00 AM

I have laptop.
I read that cable assembly is 37 dollars, no biggy.
But when I read about the data stream provided by software, i was intimidated because disclaimer says, interpretation is on the owner. I was expecting software with nice easy graphical interface. What software have you seen and what was the enviroment like? Was it easy to use like a windows enviroment or just lots of bitstream info?

Smily