1993 LT1 Intermittent Crank-No Start

[Mark E.]

Re: 1993 LT1 Intermittent Crank-No Start

With phone support from Ed Johnson (thanks Ed!) I’ve reached a diagnostic conclusion and want to run it by the experts here.

Beginning with the “Engine cranks but doesn’t run” A-3 flowchart in the FSM:

Is RPM indicated on Tech 1 during cranking?
I don’t have a Tech 1 but no RPM indicated on car’s tach. To be thorough, I ran through YES and NO branches and compared conclusions:

NO RPM Indicated
Voltage on terminal C of distributor connector while cranking? YES
Continuity between terminal D and ground? YES
This means faulty distributor or distributor connection

YES, RPM Indicated
Spark at spark plugs? NO
Use Chart C-4 (Ignition System Check)
Spark at coil secondary cable? NO
Voltage at Ignition Coil Module terminals A and D? YES
Voltage at Ignition Coil Module terminal B (4v AC) NO
while cranking?
Low resolution signal while cranking? NO
(Ed’s method to determine this w/o a Tech 1: Turn ignition on; fuel pump primes to 40 psi; bleed pressure while keeping ignition on; crank engine. Pump did not activate ==> no low resolution signal.)
(Dave Perry’s method: Same as above without bleeding fuel pressure. Same result.)
Voltage at distributor connector terminal C? YES
Is distributor connector terminal D grounded? YES
5v at distributor connector terminal A? YES
5v at distributor connector terminal B? YES
This means faulty distributor or distributor connection

So same conclusion either way (with and without RPM signal). The harness connectors at the distributor and on the intake manifold look clean and dry and have continuity so my conclusion is the distributor is faulty.

Answering Dave’s earlier question: The spark plugs are dry (I checked two of them).

Feedback welcome.

Thanks again!

[Floyd B.]

Re: 1993 LT1 Intermittent Crank-No Start

Mark,

My Tech II came with these connectors. The one on the top is the ODBII. Do any of these look like a match to your 93's port?

IMG_3072.jpg

[Mark E.]

Re: 1993 LT1 Intermittent Crank-No Start

Floyd,

Thanks for sharing this. The third from the top may be a match... a 12 pin with an external locator slot in the center.
Do its instructions say something about compatibility?

[Floyd B.]

Re: 1993 LT1 Intermittent Crank-No Start

It claims "Support for on-board diagnostics on all GM vehicles 1992 thru 2014." But I would try it before I bought one.

[Mark E.]

Re: 1993 LT1 Intermittent Crank-No Start

It claims "Support for on-board diagnostics on all GM vehicles 1992 thru 2014." But I would try it before I bought one.

I think I'll buy an Asian Tech 2 and try it. There's quite a few overseas suppliers selling these for under $300, and as you said, they claim compatibility with 1992-2014 GM cars. I'm hoping it will help with diagnosing future problems, especially since the FSM diagnostic flowcharts frequently refer to a Tech 1 reading.

Can you (or another reader) recommend a source? You mentioned a US distributor which would be nice.

[Floyd B.]

Re: 1993 LT1 Intermittent Crank-No Start

I commend your attitude. While the fact it supplies an ALDL/ODBI connector is a good indication it provides at least some support, I would still want to try it first. There are a few Tech I's on ebay but I wouldn't buy one until I verified the Tech II limitations on ALDL/ODBI equipped vehicles. The Tech I has much less functionality than the Tech II and only supports '91 - '95 vehicles equipped with ALDL ports.

I suppose the worst case is: sell it at a small loss on one of the Corvette forums. Or you can use it on all your 1996 - 2013 GM cars.

I bought mine several years back from an ebay store located in the US but I don't see any ebay listings from US sellers. Perhaps you could fined them at a reputable online automotive tools store? I've ordered plenty of items directly from Chinese sellers on ebay with no problems, but never anything quite this substantial. I also see folks selling slightly used ones on CF.

[Joe L.]

Re: 1993 LT1 Intermittent Crank-No Start

I commend your attitude. While the fact it supplies an ALDL/ODBI connector is a good indication it provides at least some support, I would still want to try it first. There are a few Tech I's on ebay but I wouldn't buy one until I verified the Tech II limitations on ALDL/ODBI equipped vehicles. The Tech I has much less functionality than the Tech II and only supports '91 - '95 vehicles equipped with ALDL ports.

I suppose the worst case is: sell it at a small loss on one of the Corvette forums. Or you can use it on all your 1996 - 2013 GM cars.

I bought mine several years back from an ebay store located in the US but I don't see any ebay listings from US sellers. Perhaps you could fined them at a reputable online automotive tools store? I've ordered plenty of items directly from Chinese sellers on ebay with no problems, but never anything quite this substantial. I also see folks selling slightly used ones on CF.

Floyd------


Several years ago I bought an Innova 3140 Scan tool. It's supposed to be for both OBD 1 and OBD II systems. It has a variety of connectors and cables for OBD1 systems across several different vehicle makes. There is a single 14 pin connector/cable for OBD II systems. Even with all the connectors and cables for OBD I, I have found it to be pretty useless for OBD I systems.

[Gary C.]

Re: 1993 LT1 Intermittent Crank-No Start

Vertonix Tech 1 on ebay https://www.ebay.com/itm/40404978709...AAAOSw9lhjl5ji

[Mark E.]

Re: 1993 LT1 Intermittent Crank-No Start

I commend your attitude. While the fact it supplies an ALDL/ODBI connector is a good indication it provides at least some support, I would still want to try it first. There are a few Tech I's on ebay but I wouldn't buy one until I verified the Tech II limitations on ALDL/ODBI equipped vehicles. The Tech I has much less functionality than the Tech II and only supports '91 - '95 vehicles equipped with ALDL ports.

I suppose the worst case is: sell it at a small loss on one of the Corvette forums. Or you can use it on all your 1996 - 2013 GM cars.

I bought mine several years back from an ebay store located in the US but I don't see any ebay listings from US sellers. Perhaps you could fined them at a reputable online automotive tools store? I've ordered plenty of items directly from Chinese sellers on ebay with no problems, but never anything quite this substantial. I also see folks selling slightly used ones on CF.

There are a couple of eBay vendors that ship from the US (days instead of weeks lead time) and offer a 30 day return policy. They claim to be a clone of Tech 2 and Tech 1 functionality supporting 1992-2013 GM cars. So I'll give it a try and let you know how it works on a 1993.

[Mark E.]

Re: 1993 LT1 Intermittent Crank-No Start

Floyd------


Several years ago I bought an Innova 3140 Scan tool. It's supposed to be for both OBD 1 and OBD II systems. It has a variety of connectors and cables for OBD1 systems across several different vehicle makes. There is a single 14 pin connector/cable for OBD II systems. Even with all the connectors and cables for OBD I, I have found it to be pretty useless for OBD I systems.

Joe,

As Floyd suggests, look for a scanner that runs GM Tech 2 software. This supports 1992-2013 GM cars, supposedly with the same functionality enjoyed by the technicians back in the day.

Check out this 1996 GM training video announcing the Tech 2 is replacing Tech 1, and saying it supports OBD 1 cars.

https://www.youtube.com/watch?v=l1YeT9a9ZOo

[Mark E.]

Re: 1993 LT1 Intermittent Crank-No Start

Vertonix Tech 1 on ebay https://www.ebay.com/itm/40404978709...AAAOSw9lhjl5ji

This is an original Tech 1.

It looks like the choices are an original Tech 1, original Tech 2, or a new Tech 2 clone.

[Gary C.]

Re: 1993 LT1 Intermittent Crank-No Start

GM Tech 2 came out in 1996 here's a GM Training video https://www.youtube.com/watch?v=l1YeT9a9ZOo

Gary
....

[Floyd B.]

Re: 1993 LT1 Intermittent Crank-No Start

You should be OK as long as the seller has a reasonable number of completed sales with a +95% positive rating.

[Gary C.]

Re: 1993 LT1 Intermittent Crank-No Start

The OBD2 website generally has good products. https://www.obd2tool.com/goods-150-B...ZU-Holden.html

There are several PDF's that can be downloaded at the bottom of the product pages.

Gary
....

[Mark E.]

Re: 1993 LT1 Intermittent Crank-No Start

Update: I purchased a new Tech 2 clone from a US distributor for $394 plus tax with a 1 year warranty, free 7 day shipping, accepts returns if not satisfied and even pays for return shipping. It was preloaded with software for 1991-2013 GM cars (most of them) and was supposedly tested before shipping. It shipped from Houston and I received it in 3 days.

I've only seen videos and photos of "real" Tech 2 scanners, but it looks identical and feels like a quality, robust piece. (Aside: Isn't it amazing that Asian suppliers are faithfully cloning a 25 year old electronic device?). I've only had it for a day, but assuming it doesn't suffer an early life failure, this seems a good option compared to buying an original, used piece that may cost more.


20230127_112213.jpg 20230127_112157.jpg

The immediate reason I got this was to be more confident diagnosing the crank- no start problem. Going through the diagnostic flowcharts in the FSM, there are two questions I struggled with:

First, "Is RPM indicated on Tech 1 during cranking?" Ed (it turns out he's a 20-plus year GM technician) advised that the car's tach is also an indicator. Well, neither the tach nor the Tech 2 shows RPM during cranking. Here's the Tech 2's screen while cranking:


20230127_111947.jpg

For some reason, it also reads 15 RPM with the engine stopped. So I interpret this as no change (no RPM signal) while cranking.

Once this question is answered, the flowchart asks about voltage at terminal "C" (YES) and continuity between terminal "D" and ground (YES) for the distributor electrical connector. Flowchart conclusion: "Faulty distributor connection or faulty distributor". I visually checked and cleaned the connectors at the distributor and intake manifold, with no change.


The other flowchart question I struggled with: after an RPM signal is confirmed (it wasn't but for illustration): "Is a Low Resolution Signal on Tech 1 indicated [while cranking]"

Both Dave and Ed advised this can be determined by turning on the ignition to check initial prime fuel pressure (YES), relieve fuel pressure while leaving ignition on, then briefly crank engine. If the fuel pump energizes again, then this suggests there is a low resolution signal from the distributor. In my case it didn't energize. Confirming this, you can see the Tech 2 shows no Low or High Resolution Signal from the distributor.

I interpret this as meaning the ECM is providing power and ground but there's no return signal from the distributor.

Interested in comments and advice.