TBI HELP, stuttering under load. Tried everything.

[NastyBuzzard]

Hey guys, I'm new to this site, and I come with some issues! If you don't want my history scroll to the bottom for the issues!

Some history for you. I bought this 1987 GMC V1500 4x4 5.7 TBI 700R4 right at 10 years ago with the help of my great grandmother who has now passed away. I swore to never get rid of this truck considering the sentimental value it holds between her and I.

When I first got it, I was told had rebuilt engine and trans, blah blah blah, (took valv covers off and it was disgusting, so lied about all that.) two months later cat is completely stopped up and backfires through engine and then it starts burning oil. Ran good all the way through high school, except the trail of black smoke, then it developed a fluctuating idle that took me a year or probably more to find. Anyways, I replace everything and it turned out little hose in gas tank had split. Then I swapped in built 355 carbed with about 420 ponies and truck was fun and played in the mud and had a great time.

About 1 1/2 years ago I decided to transform the truck all the way back to stock, or atleast stock for when I bought it. I pulled the old 350 TBI i took out and took it apart and cleaned it and was prepping it for machine work, then a week later went to pick it up to take it and my dad scrapped my whole engine and every part that went with it b/c he needed money. He tried to lie and saw that block was cracked or something, anyways... Found a 350 tbi engine in GA that had 80k with blown headgasket. Dissassembled engine, cleaned everything, put new rings and all, re-did heads, used serp setup and got new alternator, 02 sens, and various other goodies. Started engine got it running good, insured it, went for a drive and got 5 miles before trans blew. About 6 months later, installed rebuilt 700r4 and had some shifting issues. Took insurance off and parked it b/c was too busy.

About 4-6 months ago, insured it and started driving it on the weekends. Fixed trans by installing shift kit, new kickdown cable, and did a drac mod to fix speedo. Ran good for a while, minuse a few hickups. Swapped rearend & front end to ones from co-worker that had 10k on all bearings, new eaton posi for rear and 3.42 gears, so upgraded from 3.08s. Truck runs ok, still rich, like 10-11 mpg w/ 31 tires.

HERE IS WHERE SH*T GOT REAL: About a month and half ago, I parked truck on a hill at my house and it sat there about a week before I went to drive it next weekend. Crunk it up, took a while which isn't usual, bc it normally fires as soon as I turn key. Idle fluctuated a lot, couldn't settle on idle, when it got warm it would shut off most of the time when I put in gear.

Checked distributor, now when I originally was timing this truck it, it would not run at TDC, had to turn cap clockwise about 1/4 of a turn and there it ran perfectly find before parkin on hill. Swapped distributor and new distributor was timed at TDC 0* with est unplugged and timing was set and ran a lot better like that but still shut off when warm in gear and stumbled at stoplights.

Tested everything, radjusted valves, swapped out sensors, and tps, iac and all and nothing fixed it.

Well 3 weeks ago I was working on the truck and after everyone was telling me to change computer out, I started thinking, last time there was a problem I couldn't fix it was that damn hose rotted in the fuel tank. Next day I stopped and bought a fuel pump for the truck.

Installed it and truck started making knocking noises, thought it was from a bent fuel like behind tb, so I tried to debend it and punctured it. After that I took a break that night, checked oil and everything trying to determine knock but found nothing.

Next day I fixed fuel line, and started it up and kept knocking. Tried tweaking timing and everything and ran it for about 30 sec while adjusting, then when nothing changed, I checked oil again and wham!! Filled with coolant... Blown Head Gasket.

Next week I fixed head gasket, started up and was running funny, had little noise, re-adjusted valves, noise was gone. Tried to swap ICM under dist cap and put wires backwards and blew that, so ordered dist. Got it and installed it. Then developed 2 cold cylinders #2 and #3 I think, #2 for sure. Turns out valves too tight, readjusted them last weekend and ran smooth for about 3 hours that night, thought I had all problems fixed, hooked truck up to laptop, no codes, winaldl data looked great. Went to bed happy.

Monday, I got in the truck to put some miles on it, all happy and giddy, get down the road and it starts to stutter, then it got worse and worse and began running bad under load. Limped it home. Checked aldl data, everything seemed within spec for the most part, knock counts were high. I swapped out more sensors, and nothing.

Well last night I was checking everything again, re-did grounds at thermostat housing, re-did grounds at back of intake on pass side, noticed fuel line was a little bend in the steel braided part, took it off, debent it. Took wires off, checked them, took cap off and rotor button (which was new was a little chewed on the inside...??? NO clue) put another rotor button on it. Put it all back together and checked all grounds and everything and fired it up.

ISSUE NOW.
Hooked up laptop, all data seemed good, was purring like a kittin idleing in the car port. Got real excited, let it warm up and still sounded good. Took it for a drive with laptop hooked up and the more I drove it, the worse it got. Checked date and my knock count was 100++ ??? Did some research and knock sensor makes est retard timing when knocks detected and makes sens while driving it is getting worse when it keeps detecting knock.
Reset, computer by unplugging battery and idled smooth, with ign count knock reads 0 but when i crank it, it reads around 4-6 ( i do have headers and heard that starter can make it jump on crank as well). Took it for a drive and got worse and worse, stuttering and shaking around 45-55 but over 55-60 truck runs a lot smoother but still feels like power is down. So right now smooth rolling till about seems ok, lack of power, truck shakes in OD and when torque conv kicks in, clears up 55-60 but still isn't right.

Any ideas??

It has new distributor, fuel pump, coolant temp sensor, plugs, and checked everything I know to check. I do not have a fuel pressure gauge, vacuum gauge, or a way to check compression.

Tell me what to do and Ill try it, I can also get WINALDL data because I do have the cable.

HELP??

[speedygonzales]

Does this rube goldberg have any O2 sensors?

[NastyBuzzard]

Yes, it has a single wire O2 sensor on driver side header.

[LynnJr]

Sounds like my truck.I had absolutely no uphill power.
If it has a spark knock sensor make sure the wire going to it plugs in well with no chunks of the plastic missing.
If it has a egr sensor unplug it and take it for a ride.How does it run unplugged?
These trucks crack heads like most people change there socks so next time you think its a head gasket look at the chamber of the head for obvious splits.

[speedygonzales]

Try unplugging the O2 and see how it does after it warms up.

[NastyBuzzard]

The knock sensor looks to be in great shape and I suppose working correctly as it is counting knocks...

Heads cracked, well when I did head gaskets I looked heads over pretty thoroughly and got them decked and never saw any cracks... Could have been hidden though.

I've try unplugging egr and solenoid and no changes, EGR seems to be working correctly, if I push up on it with my finger engine idles down or ****s off.

02 sensor appears to have good readings, at idle in open loop it varies from .4-.5 volts and while driving in open loop it goes from .1-.9 through the rpm range. I will try unplugging it and taking it for a drive after work.

I think it has to do with it counting knocks from knock sensor and retarding timing and making it run like crap. I replaced distributor Bc on my msd one I plugged wires into icm backwards and it blew the wires off the icm so destroyed it. That may have burnt up another sensor as well, not sure. This truck has me and several others stumped...

[LynnJr]

Mine was counting knocks and killing the timing so it had no uphill power at all;
It was a combination of things The spark knock sensor was working intermittently so it and the pigtail got swapped out first.Next was the EGR solenoid but I replaced the EGR because it had alot of miles on it.
Next was the harness had a wire on it that would open going uphill and the dealership found that after I gave up on it.

[NastyBuzzard]

A wire that would open going uphill? You mean wire had shorted or broken?

So replacing knock sensor and plug, and then egr solenoid and egr didn't help?

My egr works, I assume, when I push up on it the truck idles down or shuts off.

My thing is, I don't know how to check to see if knock sens works properly, it's counting knocks, and plug and it looks too be good. Wish I could bypass it..

Also, I'm worried when dist wires popped on icm if it didn't pop the ECT or est or ruin knock, but I don't know how to tell. I've thrown $600 at this truck already and it has gotten better but still not drive able in my opinion. All that money could have gone to 5.3

Everyone's telling me to swap back to carb but I really don't want to. I want it to be stock with the tbi set up.

[speedygonzales]

Originally Posted by NastyBuzzard

02 sensor appears to have good readings, at idle in open loop it varies from .4-.5 volts and while driving in open loop it goes from .1-.9 through the rpm range. I will try unplugging it and taking it for a drive after work.

I think it has to do with it counting knocks from knock sensor and retarding timing and making it run like crap.

First I think you mean CLOSED loop not open. The knock sensor itself can be checked to see if it works but It seems your problem is the PCM thinks it's knocking when it actually isn't. So testing the knock sensor to see if it recognizes knock would mean nothing. Back to that in a minute.

I suggested you disconnect the O2 since you mentioned it is good while cold and gets crappy when hot. The O2s are not read until it goes into closed loop. Disconnecting them (it) will force it back into open loop so if the problem is a closed loop control issue, this will prove it.

The knock sensor can be checked by KOEO check the knock counts by wrapping on the engine block with the handle of a screw driver.

The knock sensor can be bypassed with a resistor to eliminate it from from the circuit and seeing if it is causing an issue.

[NastyBuzzard]

Ok I will try to unplug 02 and see what happens.

Got replacement ECM, est module, and compression gauge, fuel press gauge but no T to connect with.. So going to try all that as well.

[speedygonzales]

Originally Posted by NastyBuzzard

I've thrown $600 at this truck already and it has gotten better but still not drive able in my opinion. All that money could have gone to 5.3

Originally Posted by NastyBuzzard

Got replacement ECM, est module, and compression gauge, fuel press gauge but no T to connect with..

These two posts seem to contradict each other. You're upset about pouring money into the vehicle and yet you run out and get a replacement ECM? and what ever a EST is? Then get the test equipment?

There are way more tests you can be doing before you should ever consider getting any parts. FWIW remember just starting up the vehicle and checking pressure is not good enough. You want to know what the pressure is when the problem is occurring.

Compression is helpful but doesn't tell the full story. A leak down test will give you a more complete idea what's going on.

Are cylinders dropping out when the problem occurs? Get the point?

[NastyBuzzard]

Nah I didn't go out and buy ECM and all, and not really whining about money just don't like to see $$ put in and not fix or change anything. I borrowed all that from a guy who had tbi on his 91 big blazer with 350 tbi but could never get it right so he went to carb.

I tried unplugging o2 and driving it. Wasn't as bad but was backfiring/popping through exhaust and still stuttered like hell up hills and overall drove like crap with not all power there.

[Mr_Rich]

It sounds to me like an ignition problem and not a TBI problem. I thought I would swap out the dist. module with an Accel unit one time. It was over-advanced and cutting out. That lasted as long as the test drive and I went back to the stock module. I have a Hypertech chip in my ECM and I'm happy with the performance.

[NastyBuzzard]

ICM is stock style application, using one that came on replacement distributor. I agree it feels/acts/seems like ignition/timing issue.

Just did compression test on pass side and all 150+ avg around 155, still need to do drivers side. Tested all wires as well as the coil and all seemed good.

While driving it cool it seems to miss less and more I drive it the more it misses. Hills kill it and after it gets fully warm going in OD w/ torque conv lockup at 45-50 it shakes and stutters. Around 60-65+ seems to level out some and run better. I'm so stumped fellas, and very depressed and motivation is dwindling down.

[speedygonzales]

Hows it idle when it's hot? does it seem like it's down on a cylinder? If it runs crappy at idle when hot, pull a plug wire one at a time to see if it's not firing all cylinders.

[Mr_Rich]

One thing that might help you is a dial-back-to-zero timing light. You can use it as a tool to check the timing advance curve. It almost sounds like you don't have any ignition advance. The truck will run with the tan wire unplugged, but I wouldn't try driving it anywhere. At IDLE, my truck will read about 20-25 degrees of ignition advance WITH the tan wire connected. I read that on the dial of the timing light with the hash mark at zero on indicator of the timing cover. You could map the advance curve at different rpm levels. I bet it will make a difference.

[NastyBuzzard]

I took it to a mechanic and he hooked it up to his scan tool and couldn't find anything abnormal. IAC did hang up but went back down when tapped with screwdriver.

He feels like it was skipping out of pass side exhaust but I dont have true duals, just y pipe into 1 in 2 out flowmaster, no cats.

First we used his craftsman timing light with dial to set to TDC 0 degrees, and its perfectly on 0. Didn't check how far est is advancing/retarding it but when I did it before with timing light the mark was reading at about 12 oclock/1 oclock on the harmonic balancer, and wasn't really fluctuating but that was just at idle not after being driven.

Then tested all wires by pulling them off cap, and off plug. Then used a spark plug tester between wire and plug and all seemed to be working in good condition.

Then checked compression on pass side and at first we thought cracked head bc gauge leaked down but turned out to be a faulty gauge, held steady at 150-160 with my gauge.

At idle you can barely feel a skip every know and then when cold, more prominent when you put it in gear and hold break. However, after driving truck and it being warm then coming to a stop at idle you can feel it a little more than when cold.

[Mr_Rich]

After checking off everything you listed it still sounds to me like you're not any ignition advance. Statically timing the truck is not telling you anything. Mapping the advance curve at different rpm levels is the first thing I would check before you go any further. It sounds like you've done everything else and it checks out okay.

[NastyBuzzard]

How do I map the curve? Is there a program like WinALDL that allows me to do this? The mechanics scan tool was doing it but I can't just borrow it and he charges for his time.

[Mr_Rich]

Originally Posted by NastyBuzzard

How do I map the curve? Is there a program like WinALDL that allows me to do this? The mechanics scan tool was doing it but I can't just borrow it and he charges for his time.

Normally with a basic timing light the balancer marker runs off the scale as soon as you hook up the tan wire.

Mapping the advance curve actually very easy to do with a dial-back-to-zero timing light. You don't have to disconnect anything. Hook the light up like a basic timing light. (A tachometer would also be helpful.) The one I'm talking about has a dial. Run the truck at different rpm levels and read the dial on the timing light as you dial the timing to the 0 BTDC marker with the timing light. I hope I haven't confused you. In these days of computer controls these tools I mention are obsolete. With this timing light I mention you should be able to read the timing if you gun the engine to about 2500 to 3000 rpms and I think the timing should be in the neighborhood of 40+ degrees BTDC. If it isn't I think you found the problem.

Right now a friend of mine is painting my truck down in LA. I can't really illustrate with pics what I'm describing without my truck at this time.

[NastyBuzzard]

Ok, so lets say that I do that test and it doesn't do like you say. What would cause that problem?

[NastyBuzzard]

Also, forgot to mention during rebuild we swapped in roller setup with vortec cam. Every where I looked and asked everyone said it is ok to swap it in there, and it also ran good for months until this whole debacle started.

[Mr_Rich]

Originally Posted by NastyBuzzard

Also, forgot to mention during rebuild we swapped in roller setup with vortec cam. Every where I looked and asked everyone said it is ok to swap it in there, and it also ran good for months until this whole debacle started.

Is this the stock cam with the roller setup? Shouldn't be a problem if it is. I was talking about the ignition module at the base of the dist. That's the one you have to make sure you coat with dielectric grease so it doesn't overheat. The ones I've known to fail leave you on the side of the road. I know if the ignition isn't right it can also make it feel like the vehicle you're driving is against a 100 mph headwind. Sound familiar?

[NastyBuzzard]

Roller setup with a vortec cam, used melonizd gear on distributor to compensate for that.

Ignition control module is new with distributor.

Also, idle fluctuates but pts and iac values are staying the same??

[LynnJr]

When these trucks age they make your hair fall out.
There are two temperature sensors on your truck.One is on the drivers side head with a green wire and the other is next to the thermostart with two wires.
Check those two wires for cracks and replace if necessary.
Next on the throttle body itself there is a rubber grommet under the air cleaner housing.Those wires run the fuel injectors and will crack from age.Check those out and wrap with vinyl tape if needed.

When it is cold and fresh for the day how does it run for the first two minutes?
Does it run smoothly then start to act up as it warms up at a certain mph?
I called comp cams and they said no cam but a stock cam could be used and still get any vacuum.What cam are you using?