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Need TBI troubleshooting help

Madbomber88

Madbomber88

1/2 ton status
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Hi guys,
First a little background on the truck
1988 V30 (1 Ton 4x4 Dump Truck, manual tranny, TBI 350)
This is the mountain neighborhood plow truck and never goes off our private roads. I did a complete rebuild of this truck this fall, all major systems and sensors are new, to include:
Rebuilt stock TBI
Long tube headers with heated O2 sensor
Coolant temp sensor
IAC
Oil pressure sensor
MAP
TPS
EGR Valve
EGR Solenoid
Speedway Motors TBI wiring harness
Distributor (stock replacement)
Ignition Coil
Plugs/wires
Fuel pump

Here's the problem. Truck starts and runs/idles pretty well. It does have a delay/say when you open the throttle. I have all the vacuum lines capped at the TBI except for the PCV port and MAP port. The only sensor I have not changed is the ESC module, but one is on the way.

When I check the timing (using the correct method by unplugging the timing wire), it runs very very rough and will cut out at 0 degrees. It only idles smooth at a ridiculous amount of advance, that is off the indicator plate. It will run decent at about 8 degrees advanced, but anything close to 0 gets a rough idle.

If I unplug the ESC module, there is no noticeable difference in anything. Is that normal? Also, the EGR valve doesn't seem to be doing anything. Normal? When I run a scan, I get about 6 codes, relating to EST, Coolant temp sensor, inlet air temp, etc...but I'm not sure how accurate this is. There is a TON of vacuum at idle on the PCV port.

It runs pretty good at that advanced timing, but with all the codes and the sag/hesitation when you open throttle, I am assuming there is an issue and better performance to be had.
Any ideas?
Thanks in advance!
 
For the timing being off issue, how monkeyed with is the motor? Rebuilt?

Wondering if your timing issue isn't outer ring of the balancer slipping, or wrong timing tab.

That's the obvious problem, that needs fixed first. Get that thing on #1 TDC, and figure out why the balancer isn't lined up.
 
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It is a rebuilt motor, but TDC in the engine/distrubutor/harmonic balancer does all line up together. I guess my biggest question is if it sounds right and runs right, is there any reason not to leave it at such an advanced timing? This truck is a plow truck only for our local HOA in the mountains so it never sees pavement or anything over 15-20 MPH...
 
I'd say the reason is because something is not right. Base timing on these things is 0-4*, if you aren't there, something is wrong. Like you say, it really doesn't affect anything as long as it's timed right, but you have other problems too.

I don't see how everything can be lined up at TDC (are you saying timing tab lines up too) if it won't run at 0*, but runs ok higher.

I've never really dealt with advancing/retarding the cam timing, but I would assume that could cause this as well.
 
dyeager535 said:
I'd say the reason is because something is not right. Base timing on these things is 0-4*, if you aren't there, something is wrong. Like you say, it really doesn't affect anything as long as it's timed right, but you have other problems too.

I don't see how everything can be lined up at TDC (are you saying timing tab lines up too) if it won't run at 0*, but runs ok higher.

I've never really dealt with advancing/retarding the cam timing, but I would assume that could cause this as well.
Click to expand...

It will barely run at 0*, but it dies pretty quickly. It just runs super smooth at what I would say is about 12*. I guess the harmonic balancer could have slipped a bit when the previous owner had the engine rebuilt. Any sure fire way to tell?
 
Surefire is to put it at #1 TDC and make sure the 0 mark on the balancer aligns with the timing tab. But you are saying that is the case now? This of course assumes you have the right tab. I know GM used 3 or so different tabs, but don't know why different were used, and if it was year split, or application specific.

Maybe someone else can chime in, but only thing I can think of if everything on the balancer/tab/TDC check out, is the cam not being installed at 0*, vs + or -. Its not uncommon for people to install a cam advanced or retarded as I understand, perhaps the PO thought it would be a good idea to do on an FI engine, not knowing any better.

This is a consistent problem, that didn't just crop up?
 
It could be the wrong tab...who knows? I don't know if it was a constant problem because when i got it, it had tons of problems so I did a complete rebuild of just about everything. It runs a million times better than it did, so I am just wondering if there is any damage I am doing if it seems to runs great but the timing is way off (according to the indicators). So far the road tests show that is runs great. The timing indicator on the harmonic balancer is about 3 inches before the tab...
 
The system is fairly good at keeping itself happy under cruise conditions, if it's running lean under heavy throttle there isn't much it will do to stop that unless it starts knocking, at which point the knock sensor will start retarding timing, reducing power. If it's bad enough you will feel it, a couple degrees and you won't.

Plug wires are routed correctly? All of the cylinders are firing? EFI can do a good job of covering up dead cylinders.
 
As far as I can tell yes. I will be testing the voltage at all the sensors this weekend to see if there's anything obvious. I'll also spend some time with the timing. At 0* it just idles like crap and will die. At a few degrees advanced it is better but a lump idle. Runs smooth as glass where it's at now. I do want to make sure all the vacuum lines are good though. I have them all capped except for the PCV and rear MAP port. I did away with the air pump and fuel vapor canister.
Thanks for all your help
 
Is your vapor line vented at least? I don't think that would cause a particular issue, but if plugged, I suppose it could make it harder on the pump.

I see the fuel pump is new, so not likely, but IMO never hurts to check pressure either. Not sure if low pressure is something timing could help hide or not.
 
I got my new ESC module and installed it today. I then disconnected the battery, undid the timing wire, reconnected the battery, started her up and adjusted the timing to be dead on with the indicator. I then shut her off, connected the timing wire, started her up and saw that the timing now showed it at 4* advanced at idle...the idle was relatively smooth, but when I shut it off and restarted it, it didn't want to stay started. So does this tell us anything? Is it normal for the ESC to advance the timing 4* at idle??
 
I could be wrong (just looked up some info, does not appear I am), but I don't think the ESC does anything other than retard timing when the knock sensor "hears" detonation. Should not affect timing under normal conditions.

However, you should be at ~20* at idle with the bypass wire connected, which raises the question of why it's not.
 
So you're saying without the wire connect, time it to 0* (assuming indicator is correct), and then when the wire is hooked back up, it should be at 20* advanced?
 
Yep. I'd have to look at the programming of the TBI for timing at idle, but it's most likely up near 20*. On the LOW end I'd think 15* or so.

This is one reason EFI rules carbs...you can (and GM did) run extremely high idle "base" timing without the penalty of affecting timing during other engine operating conditions.

I'll see if I can't find something showing the timing used in GM's programming for TBi that vintage.

Can't find anything I can view here, its going to be way higher than 4* I guarantee it.
 
dyeager535 said:
Yep. I'd have to look at the programming of the TBI for timing at idle, but it's most likely up near 20*. On the LOW end I'd think 15* or so.

This is one reason EFI rules carbs...you can (and GM did) run extremely high idle "base" timing without the penalty of affecting timing during other engine operating conditions.

I'll see if I can't find something showing the timing used in GM's programming for TBi that vintage.

Can't find anything I can view here, its going to be way higher than 4* I guarantee it.
Click to expand...

So maybe I don't have a problem at all then!?
 
If it will run at 0* with the bypass disconnected, then jumps way up after you reconnect/restart it, that's normal.

What you said was happening though was that it wouldn't idle at 0* with wire disconnected, which is not correct.

This of course, assumes your truck is designed to have the base idle set at 0*...apparently some applications it was a bit more, but it is on the sticker on the core support.
 
do yourself a favor and check compression i had similar issues and found the headgasket to be failed but not in a water jacket.
 
I've had fuel pressure issues on mine and timing will hide it. I replaced ever sensor on mine until I realized I had low fuel pressure. I changed my fuel pump a few times until I realized I had a crappy fuel pump relay that was burning up pumps. I bumped my timing up and got a good idle and ran decent. I put a new pump in and the idle was high. I'm no mechanic or expert just sharing personal experience.
 
I am going ask a very basic question, because I have seen a lot of confusion when somebody says they set TDC.

How did you set it at TDC? The right way is with the valve cover off so you make sure you are on the compression stroke, then check the cylinder for top. I use a zip tie to feel what the piston is doing.

It sounds to me like you might be 1 tooth off on the distributer timing.
 
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