Paging Patgizz and other GM tbi knowledgeable

Soccer Mom Challenge hopeful Jean Clyde Damn Van won't idle from startup. Even when warm if shut down wont idle again unless driven but not well. May hunt or stall. When under load may load up and backfire through throttle body(which is interesting to see/feel when driving with the dog house removed), though not consistently. New MAP, no vacuum leaks, EGR bypassed as the carbed manifold has no provision for it. Set timing to 0 with signal wire disconnected as per procedure. Does not go to 16 degrees when reconnected as it should, but will show 30 degrees of advance when throttled up. This is a very simple system, what am I missing? ECT? Unplugging it causes a change but not much. Driving with MAP disconnected no change either. New Bosch O2 sensor as well. Should I get a chip that ignores the EGR system to pass inspection?

Where's the bang head against wall emoticon?

1992 GMC Safari, older GM crate motor rebuilt with RV cam. Injectors, knock sensor, exhaust manifolds, wires and distributor from truck at salvage yard.

I'm hoping for a hail Mary here. Help me Obi-Wan Kenobi, you're my only hope.

Sounds like a faulty ignition control module. Or a bad ground on the harness, probably at the thermostat housing.

I have had nothing but bad luck with Bosch O2s lately. Especially the cheap universal units.

In reply to vwcorvette:

I can't help with the issue but I can give you this...

Dusterbd13 wrote: Sounds like a faulty ignition control module. Or a bad ground on the harness, probably at the thermostat housing.

According to my research it wouldn't run at all with a faulty module, but I guess it could be questionable. All grounds are clean and good.

Knurled wrote: I have had nothing but bad luck with Bosch O2s lately. Especially the cheap universal units.

Vehicle specific used.

Nick (picaso) Comstock wrote: In reply to vwcorvette: I can't help with the issue but I can give you this...

THANK YOU!!!!

Shot in the dark here, unscrew the IAC from the throttle body and clean the passage, it could be stuck shut. And, have you checked your fuel pressure?

06HHR wrote: Shot in the dark here, unscrew the IAC from the throttle body and clean the passage, it could be stuck shut. And, have you checked your fuel pressure?

IAC passage clear and replaced with spare. No change.

Have not checked fuel pressure.

I've heard they will run with as little as 9 psi of course the lower you get the worse they run, what you describe is usually the result of a bad MAP sensor, at least in my experience. You've ruled that out, looks like you've done everything else, might as well check the fuel pressure and maybe take a look at the regulator in the TBI, but I've never seen one of those actually fail (knocks wood)

Could the timing marks be off?

Firing order right?

Do you have an aldl cable?

Dusterbd13 wrote: Could the timing marks be off? Firing order right? Do you have an aldl cable?

We've rechecked the timing marks a number of times. Same with firing order and wiring routing. All good.
Do not have an aldl cable for my scan tool.

Look up making a homemade aldl cable and download winaldl. I know it's a pain, but will give you access to the datastream for cheap. Then you can figure out what is going on.

Also, this is in the challenge car. I think I remember you saying that the prom was changed to a v8 prom. Is it in correctly? Did you change the whole ecm with the same service number or a different one?

Really sounds like ignition problems from what you describe though.

I would check the Coolant Temp sensor. and then the Throttle position sensor. When both went out they displayed the drivability issues you describe. and both have failed on my TBI car. they are both fairly cheap. worth taking a look at. good luck.

Its hard to say without data from the pcm. One common issue was ect sensors, they would let you run but it ran terrible. Vacuum leaks from tbody gaskets was another. Also check the spray pattern from the injectors. Orings would fail under the injector and let it dump fuel. The timing gears would wear out and let the timing move around. Make sure that there is vacuum getting to the map sensor. I've seen those little hoses clog up. That's all I can think of off the top of my head.

Dusterbd13 wrote: Look up making a homemade aldl cable and download winaldl. I know it's a pain, but will give you access to the datastream for cheap. Then you can figure out what is going on. Also, this is in the challenge car. I think I remember you saying that the prom was changed to a v8 prom. Is it in correctly? Did you change the whole ecm with the same service number or a different one? Really sounds like ignition problems from what you describe though.

Changed the entire ECM from van to pickup. Will recheck ECM numbers.

Agreed about the timing issue but it's not consistent. Weird that I can set to 0 with signal wire disconnected but does not advance to 16 when reconnected. And will show 30 degrees advance with revs.

did you change the electronic spark control module(ESC) over to the v8 one from the computer/tbi donor?

also to test coolant temp sensor so as not to just throw new parts at it, use an ohm meter. it should be around 3k at room temp and 170 in boiling water.

I tried a different cam in a TBI engine once with a stock chip and it was never happy. It did idle though, I'm betting an issue with the IAC or fuel pressure. Also, try adding a 3 wire O2 when you've got it sorted out, helped my car quite a bit to run smoother.

vwcorvette wrote:

Knurled wrote: I have had nothing but bad luck with Bosch O2s lately. Especially the cheap universal units.

Vehicle specific used.

Doesn't mean much... I've had them "bad" out of the box, install a Denso or NTK or AC Delco sensor and all is well again.

Went around with this on a friend's Audi as well (you'd think Bosch could at least get O2s right for German cars), he installed a brand new Bosch 3-wire and he couldn't get the CIS tuned right, because even though it was a heated unit the O2 just wouldn't "wake up". Finally convinced him to splice in an NTK for some application that I picked up from Summit for $5, but an O2 is an O2 so it should work... and suddenly he was able to set the DPR duty cycle.

NEW stands for Never Ever Worked. Another reason why just throwing parts at a problem makes more problems than it solves.

patgizz wrote: did you change the electronic spark control module(ESC) over to the v8 one from the computer/tbi donor? also to test coolant temp sensor so as not to just throw new parts at it, use an ohm meter. it should be around 3k at room temp and 170 in boiling water.

. I took the entire distributor from the V8 truck I got most of the parts from.

I may just toss a spare carb I have on it instead.

Lets think here, it doesn't run right When first started, but then gets better after a little time. It doesn't matter if it's cold start or hot start, so it's not temperature related. From what you're saying it sounds like it corrects itself when it gets into closed loop. So what's different on gm obd1 from open loop to closed loop? I think they ignore the o2 sensor in open loop, so I doubt it's an o2 problem.

vwcorvette wrote:

patgizz wrote: did you change the electronic spark control module(ESC) over to the v8 one from the computer/tbi donor? also to test coolant temp sensor so as not to just throw new parts at it, use an ohm meter. it should be around 3k at room temp and 170 in boiling water.

. I took the entire distributor from the V8 truck I got most of the parts from.

Esc module independent of distributor. Look it up for pic. I'd post one but on phone in garage waiting for my pcm to write

gearheadmb wrote: Lets think here, it doesn't run right When first started, but then gets better after a little time. It doesn't matter if it's cold start or hot start, so it's not temperature related. From what you're saying it sounds like it corrects itself when it gets into closed loop. So what's different on gm obd1 from open loop to closed loop? I think they ignore the o2 sensor in open loop, so I doubt it's an o2 problem.

. Agreed. But that still doesn't explain the timing irregularity. I'm at Lime Rock tomorrow. When I get home we'll verify the operation of the ECT, pull the fuel filter and check that, and I don't know what else...

Sounds like a timing issue potentially, but check the fuel pressure as well. At least on my old TBI setup, the trims for ignition and injection cleared with every key off, so it took awhile to relearn where it should be whenever it was restarted. Also, those 193 ski jump heads use a lot of timing if I remember correctly, so 30 degrees revving with no load isn't really enough. I'd figure out why timing isn't behaving as expected; that seems like a pretty solid place to start and could cause those symptoms. Alternatively, you could manually add 10 degrees of base timing and see what happens.