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1989 GMC SLE TBI 350 5.7 Runs terrible when hook to computer

 
KeyWester
I love my Chevy Chevette!
Posts: 7
Joined: 04/14
Posted: 04/07/14 07:37 AM

wayne- here's answers to most of your questions...

Throttle plate- no play at all
Throttle Adj- there is no throttle adj screw or way to adjust the throttle speed
             (I clipped a thin metal clip to the throttle lever to see what would happen-idle was ok at first, then started getting higher, after a few minutes I turned the distibutor back to 0 degrees and it ran OK for the first time set at 0 degrees. Shut off the engine and restarted- back to the same stalling and won't idle. Could not get to run right again at 0 degrees, removed clip and I'm back to the same predictable start w/ vacuum off map then reattach to run OK)
TPS voltage- 0.66v at idle, 4.29v WOT
Oxy sensor voltage- 0.240v idle, would increase to 0.550v at mid throttle
Fuel pump amp draw- 3.5A
Battery voltage after lights on 1 min- 12.7V
Battery Voltage running, lights on- 14.2V
Battery Negative to engine block- 0.001V (on 2 volt scale everytime, no matter
           where I tested on the block/ground points)
Battery Negative to body- 0.017V
Engine block to Frame- 0.02V

Other info- I have no air injection sys
         - installed new engine block to frame ground wire (old copper braided
           strap was brittle and crusty but seemed to be working)  

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KeyWester
I love my Chevy Chevette!
Posts: 7
Joined: 04/14
Posted: 04/07/14 07:40 AM

1  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 04/07/14 07:43 PM

lets check a few things.. and there are several issues..

pull the connector off the idle air control valve.. so there is a stable idle speed..

the idle stop screw is on the front drivers side of the throttle body.. behind a tamperproof plug..

Tbithrottlestopscrew Zpsdfd9ddbc

please check for vacuum leaks.. disconnect the power brake booster at the check valve or at the inline carbon filter.. plug the vacuum hose into the engine so it cannot leak vacuum.. see if it will idle then.

take a shop rag and wedge it into the idle air bypass passage.. see where the engine idles at .. it should idle slow.. but not stall..



91 Jbody 20 Distributor Zpsc3e4178d

you can... bump the engine around until the damper mark lines up with the timing pointer.. at 0 TDC..   pull the cap and rotor.. see if the pickup coil aligns perfectly with the reluctor..  this is only a 4 banger distributor.. but its perfectly aligned for base timing setting..  if the damper was set at 0.. this distributor would fire between 1 before and 1 after tdc..  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 04/07/14 07:52 PM

by the way.. this is what the oxygen sensor signal looks like on a good running motor held at a steady 2500 RPMs..  the glitch in that pattern is where my friend moved the throttle slightly ..

O2B2S1 Zps69fd0fbd

this is on an OBD2 scan tool.. unless you have access to an advanced OBD1 scan tool you probably won't see a pattern like this.. but you will see O2 sensor crosscounts..

you will with a digital volt meter see voltage from 0.09 to 0.9..  or so.. never stable..

got any air leaks in the exhaust system???

up near the exhaust ports..  

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KeyWester
I love my Chevy Chevette!
Posts: 7
Joined: 04/14
Posted: 04/08/14 09:45 AM

Wayne- before I dealt with the idle, I installed a c-clamp where exhaust manifold to exhaust pipe flange bolt was missing. I removed plug and accessed throttle adj screw. I have no brake booster vacuum, it's hydraulic assist. Front side vacuum ports are 1)PCV w/ "T" for evap canister valve, 2) evap canister and 3)egr vacuum solenoid ... I capped off all three. Back side has only MAP port, I had previously replaced MAP vacuum hose with no change, the original is back on. D/S valve cover breather is above throttle plates. Only other vacuum port is for trans vacuum solenoid and it's by itself coming directly out of the rear of the intake manifold. I had to start engine w/ timing off (as you look down at distributor, dist is rotated counter clockwise about 1"), and MAP vacuum removed.... I got my high idle and good rev's/throttle response... reconnected MAP vacuum and adjusted distributor to 0 degrees ..... adjusted idle speed and got a good idle (tps now at 0.70v), but engine won't rev up, it bogs down and wants to backfire. If I put the timing back off like when I started it, the engine rev's good, idle is high, but stalls out when put into gear. Oxygen sensor voltages are 0.250v to 0.700v at 0 degree idle, 0.300v to 0.800v with most readings in the 0.700v at low throttle (distributor had to be rotated to where it would rev). I do not have access to OBD I tool, I had previously manually rotated engine to tdc line on damper mark and aligned reluctor teeth.  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 04/08/14 09:17 PM

hook up all your vacuum ports.. i just wanted to make sure that you don't have any leaks.. the PCV is a needed leak..

does your volt meter read MILLISECOND???  so we can see what the fuel injector pulse width is..  under normal operation at idle.. 1.2 to 1.3 milliseconds..

i don't expect a lot of people to have exotic tools and meters..

check for codes..

log in.. check the link just to the left of where you log out at..  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 04/10/14 12:10 PM

Tbipinoutchart Zps18754002

1990Chevyvantbiwiringcontrols Zps281545f8

Tbiminimumidlesetting Zps14faef45

IDLE Aircountstbi Zps0a49788f

89 92 Tbiwiring Zps3a3fdf3e

and... please check the damper bolts position when you have set the timing mark to TDC.. this is just to verify that the crankshaft is really at TOP DEAD CENTER..


Sbc400damper Zps7b6410dd

you can see that there are 2 different timing mark locations on different dampers..

Chevybalancermarks  

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KeyWester
I love my Chevy Chevette!
Posts: 7
Joined: 04/14
Posted: 04/28/14 07:41 AM

There was nothing machanically wrong with the timing, damper was correct, reluctor teeth lined up, pointing @ #1 when at tdc. I tried to find the fuel pump ground, and my only possibilities I could find were the grounds I have at the alternator bracket and the front engine ground, so I cut the connectors off and replaced... no change. Time to find a fuel pressure kit that taps into the TBI. I was originally going to try to weld a fuel pressure shrader valve to a fuel filter to do this, I looked at the pro kits in my catalog .. didn't really see it ... kept looking... 4 pages down they were selling what I wanted to make, an adapter for a fuel pressure gauge that goes in place of the fuel filter on a GM TBI. ARRGGGGGG I don't know why they were selling the gauge and adapters for ford/chev/dodge quick disconnects on one page and this four pages down, but they did. Got it w/ gauge, checked pressure and had only 5 psi, dropped tank, and found I did have a fuel leak, in the tank. The 2" hose that connects the fuel pump to the output tube had a little split in it. Instead of just replacing the hose, I got a new pump and strainer, installed, getting 13 psi and it's running like a champ. So thank you Wayne for helping me trouble shoot this. To those who want to get this adapter, NAPA does sell it, made by OTC #700-2460 (I used w/ OTC gauge 700-1487) Now I get to replace the engine in another '89 GMC, this one a 22,000 gvw C6000 w/ a 5.7L carb engine, fun fun fun  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 04/28/14 05:23 PM

keywester...

just a heads up..

that C6000 5.7L motor is NOT an average rebuild.. please.. if you are going to send it out for rebuilding.   NOTE the block casting number..  the cylinder head casting numbers.. it should have a 4 bolt main block..  a steel crank.. wide parting lines. might have forged pistons with power grooves.. en embedded top ring groove in the piston thats an obvious different material..  the heads will if you look closely at the exhaust valve stems below the retainer.. will have 3/8" stems instead of 11//32" stems..  why... heavy duty small block heads have sodium filled exhaust stems.  you really don't want valve guide liners either . oversize stems are available. thats just my personal opinion..

why am i telling you this.. because rebuilder will take the heavy duty engine components you turn in for rebuilding.. and return you a LIGHT duty 2 bolt main cast crank junk piston light duty exhaust valve heads and it will last 3 to 6 months..

if you don't make them NOTE every component casting or forging number you will get back a motor that is worthless for heavy duty work..

google Hylonar.. spread or spray some on both sides of the head gaskets.. let the solvents evaporate from them for 20 minutes before installing..  CYA..

since i know where you are.. it also depends if this motor is really going to be be used as the truck was designed.. running close to the governor limit for hours at a time.

that model has a goverened 2G rochester carb.. do not touch the governor adjustment.. you can go in and change the gaskets if you can find a kit..  

let us  you that you received this.  glad you go the other running..  

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KeyWester
I love my Chevy Chevette!
Posts: 7
Joined: 04/14
Posted: 04/29/14 10:24 AM

Wayne, Thanks for the heads up. I'm aware of how special this particular 5.7 is and have been talking with the engine builder. (I'm just going to put it and a new clutch in) It's going to take them a month to build it for us from a block they have located because ours is cracked, guess that's why most people buy big ole trucks with big ole diesels  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 04/29/14 03:15 PM

glad they gave you the proper info...

i used to work at an engine rebuilding shop.. i ran the head department.

but years before.. i spent a lot of time building motors.. i happened to be there when a guy dropped off his heavy duty small block.. like you are working with and when he picked it up.. a conventional small block..

worst are the 454 marine spec motors..

some of them have OVERSIZED main bearing bores..  and getting bearings for those is almost impossible .. i know one rebuilder that just tossed the 4 bolt main 454 marine blocks in the scrap pile.  i personally would have cleaned and then painted everything up and stored them just in case.. but i am far sighted..  

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verricorob
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Posts: 3
Joined: 05/14
Posted: 05/17/14 08:42 PM

waynep- Thanks for all your help! You are awesome! I have a problem with my 1990 GMC 2wd 5.0 vin H pick up truck. This truck is totally stock and nothing but a work truck. Lately it hasn't been much of anything. It runs great for a while then it just dies! OK, you're probably going to say put in an ignition module. Done. Ran great for a couple of days then same thing, it dies. Had module checked at O'Rielly's. It's fine. To make a long story short, before I got it the fuel pump was replaced. Since I've had it, Ign module, then Reman. Cardone Distributer, fuel pump relay, New injectors, new computer,
even swapped out computer prom and what ever the other one is called from a running truck with the same computer, coil. dist cap, rotor, wires, plugs. I don't know where to go next. When the truck runs it runs GREAT! I don't think I'm getting signals to the injectors when it dies. I've got a cheap ass noid light from Harbor Freight but I think it is working. Please give me any ideas you've got. I thank you in advance for your help. If anybody else has any ideas I'd love to hear them. Thanks again, Rob V.  

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verricorob
I love my Chevy Chevette!
Posts: 3
Joined: 05/14
Posted: 05/17/14 08:45 PM

waynep- Thanks for all your help! You are awesome! I have a problem with my 1990 GMC 2wd 5.0 vin H pick up truck. This truck is totally stock and nothing but a work truck. Lately it hasn't been much of anything. It runs great for a while then it just dies! OK, you're probably going to say put in an ignition module. Done. Ran great for a couple of days then same thing, it dies. Had module checked at O'Rielly's. It's fine. To make a long story short, before I got it the fuel pump was replaced. Since I've had it, Ign module, then Reman. Cardone Distributer, fuel pump relay, New injectors, new computer,
even swapped out computer prom and what ever the other one is called from a running truck with the same computer, coil. dist cap, rotor, wires, plugs. I don't know where to go next. When the truck runs it runs GREAT! I don't think I'm getting signals to the injectors when it dies. I've got a cheap ass noid light from Harbor Freight but I think it is working. Please give me any ideas you've got. I thank you in advance for your help. If anybody else has any ideas I'd love to hear them. Thanks again, Rob V.  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 05/17/14 11:55 PM

verricorob   change the ignition switch on the column..  pain in the rear..  its cheep.. under 20 bucks.

try to recall to unhook the little string from below the shifter lever into the side of the column that hooks to the shift quadrent in the dash board.. if you drop the column without detaching it.. you may break the dashboard..


here is the inside of one that drove the owner crazy..

Ignitionswitchwornoutcontact

you can probe the BIG red wire into the coil with a test light and slowly operate the ignition switch from off to on to crank.. then back to ON.. then to off.. you should NOT loose power once you reach ON.. until you turn it off.. change the switch anyway.. and check the connectors that they are not burned..

your ignition switch will either be a part autozone wells #LS309 or LS442.. depending if its a straight column or a tilt column..
Duralast/Ignition Switch Connector This product is a fit for your:
1990 Chevrolet Truck C1500 1/2ton P/U 2WD 5.0L TBI 8cyl Part Number: 263  for the pair of connectors and some terminated wires to plug in..  

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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 05/18/14 12:37 AM

please pry open the old ignition switch once you have removed it and compare the inside to the image above..

you might be able to push the slide across to view the worn section thru the slot for the slide..

next.. do you have a timing light... tape the trigger on..  hook it up either to the coil to cap wire if you have a small cap HEI.. or a spark plug wire on a large cap HEI..   lay the timing light on the windshield under the wiper.. so you can see the flashing light from the drivers seat..  if the timing light stops flashing before the engine comes to a stop.. then you have an ignition system problem..  wiring.. coil. module.. ect..  you have seem to have changed all the other parts..so ignition switch is next. .

you may want to perform the voltage drop test.. if you have a digital volt meter...

engine running headlights on.. digital meter set to 20 volts DC..

test 1. Negative battery post to the positive battery post..  14.1 to 14.8 volts DC max..

test 2. Negative battery post to the engine block.. 0.04 volts DC max..

test 3. Negative battery post to the body.. 0.02 volts DC..

test 4. Engine block to the body. usually near the firewall.. 0.02 volts DC MAX..

test 5. Positive battery post to the underhood terminal blocks.  you could have more than one on the firewall.. could be near the wiper motor or over above the transmission dipstick tube..  0.04 volts DC max..

test 6  Positive battery post to the alternator output terminal.. 0.3 volts DC max..

test 7. negative battery post to the frame rail.. 0.04 volts DC max..  why.. because the fuel pump is grounded thru the frame rail.. not the body..  the tail lights are also grounded thru the frame rail.. since electrons flow from negative to positive.. no electrons.. no operation..

this test will take about 5 minutes to perform with a digital volt meter..  

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