Picked up a 92 RS, 305tbi.

Has a no crank issue, working on diag for starter circuit now. But before I climb down a rabbit hole, I need to know proper operation of dash lights. I have a good running 91 v6 to compare. At key on it shows the SES, INFL REST, seatbelt and security lights.

The 92 just shows the INFL REST and seatbelt lights at key on. Fuel pump does not prime. Battery volt gauge climbs to about 13v, oil pressure gauge drops below 0 and there is no crank. Other features function such as wipers, signals, lights. There is no radio in the car and the blower motor doesn't work but that may be a separate issue.

This sort of reminds me of a VATS failure but I thought the security light stayed on during that. It's been a few years lol.

More info, when I turn the key to "crank", the temp gauge climbs like my 91, showing that the car is seeing a start signal. I believe my VATS module has failed, and that's why the security light does not come on. I'm going to try and bypass the starter enable relay in the morning and see if I can get a crank. Still does not explain the fuel pump not priming but that may be another issue as well......

.... Ok, I have bypassed the starter enable relay and the car now will crank. I still do not hear the fuel pump. Almost there! Looks like it's definitely lost vats but now I'm worried about not seeing the SES light at key on.

I know I need to bypass the VATs system now for sure, as long as the ECM isn't toast. Looking at having a prom burned, can someone here point me to someone who can do that state-side?

I've inherited someones half diag'd issue. Seems this car has sat for a couple years because of this problem. My current game plan is to verify spark on crank and see if I can get the car to run on life support (starter fluid or sprayed fuel) Then pursue the no fuel pump issue. Any thoughts?

 

When I had a previous 89 Formula give me a no crank/no start issue, I was able to put a resistor in line to bypass the VATS as it died on me 1 night when I was out shopping for a car for my gf at the time. The dealer said that they could figure out what the resistance of the chip was in the key and then solder the resistor inline and it would work. It has been 20 years since that happened, so I don't remember what wire that was, but it fixed it permanently. Just a thought. I want to say it was an orange wire but don't even consider quoting me on that!!!

 

I think most car stereo places that do car alarms can do that for you. I know the guy that I go to for all of my car stereo, alarm, and remote start stuff could do it, but i'm in IL and I don't think you want to tow your car here for a simple resistor. lol

 

Vats does not kill the fuel pump . Vats also does not kill the SES light . Vats kills the starter enable relay and the injector pulse only , so if you have no two second fuel pump prime on initial key on , you have ECM issues , or power to the ECM issues , that must be diagnosed first before you go looking into VATS . I will enclose the wiring diagram for your fuel pump and you'll see there is no tie in from the pump to VATS . See that fuse that feeds the orange wire powering the fuel pump relay called "In line fuse" ? That fuse is mounted on your fender near the radiator and if you have no power on the orange wire your first check should be that fuse .....

PS , I know that wiring diagram says TPI instead of TBI but the fuel pump wiring is the same .

 

That fuse is also the memory to the ECM

 

I've verified power to both sides of the 20A inline fuse.
I've verified 12v to the orange wire of the oil pressure switch. I cannot get power to grey wire out to fuel pump when cranking, normal operation until running, right?

Fuel pump relay has power to orange supply wire, and I've verified ground to that relay. The signal wire (grey) from ecm never has voltage, as well as the prime line (red).

Jumping to the ECM B1 (orange) has battery voltage, B2 shows 3.7v at key on, it holds that voltage.

My main ground does not read continuity to the body, but shows 200+ ohms resistance. I'm going to jumper a ground in and see if anything changes.

also, i have a TPI ecm from an 88 t/a, could I swap it in to look for changes without toasting anything?

 

Update, jumpered in direct ground to A12, no change in operation.

 

I've verified power to both sides of the 20A inline fuse.
Great , that one step in the process eliminated .


I've verified 12v to the orange wire of the oil pressure switch. I cannot get power to grey wire out to fuel pump when cranking, normal operation until running, right?
No , You will only get +12V to the grey wire from the ECM closing the relay for the two second prime , and the ECM won't command the relay again till the engine starts (attains over 400 RPM) . Some cars will have the oil pressure while cranking to close the oil pressure switch , and some won't . That depends on the engine and the oil pressure switch as no two are exactly the same .


Fuel pump relay has power to orange supply wire, and I've verified ground to that relay. The signal wire (grey) from ecm never has voltage, as well as the prime line (red).
Did the ECM signal wire have +12V for two seconds upon first turning the key on , or even on initial key on was there none ? Also , no you'll never see voltage on the red prime wire , that wire goes to the ALDL and allows priming the pump from the ALDL when +12V is supplied to the correct ALDL pin .


Jumping to the ECM B1 (orange) has battery voltage, B2 shows 3.7v at key on, it holds that voltage.
I'm not sure what you mean here by "jumpering" , are you "backprobing" the connector with the ECM in place to read that voltage , or are you having to "jumper" voltage in from some other point for it to read +12V ?


My main ground does not read continuity to the body, but shows 200+ ohms resistance. I'm going to jumper a ground in and see if anything changes.
This is a cause for action , I know in your follow up post you say to ran a separate ground to A12 , but did you then verify all the other supposed to be grounded pins on the ECM to be grounded also ? Repairing all of the grounds in dash and under the hood will help you a great deal in your further troubleshooting efforts .


also, i have a TPI ecm from an 88 t/a, could I swap it in to look for changes without toasting anything?
Off the top of my head since I'm not 100% certain on this , I'd say don't swap it in till you verify that it has the exact same pinout as the one your trying to substitute . If it has the same part numbers and the same electrical pinout it shouldn't toast , it just may not make the engine run good due to the different programming . If you can verify the pinout and part numbers by all means try it if you want , but only after your 100% certain the pinouts and part numbers are the same .

 

Orange bird thank you for your time. I understand how painstaking it can be to offer this kind of help...

The ECM signal wire never shows voltage at the fuel pump relay. Not within the first two seconds of KOEO, not at all.

By "jumping to ECM" i meant moving on, next topic. The 3.7v was obtained while backprobing B2 with KOEO.
I have just now had time to pull the actual 92 TBI ECM diagrams so I will post them for reference. Tomorrow I will follow up on the ground concern. Could you point me to where the ECM grounds (A12 and D1) exit the harness loom and ground on the engine?

I notice on the diagram for ECM voltage reference it shows Pin B6 as Pass-Key Signal at 2.5v, but on the pinout diagram it shows B6 as Cranking Fuel Enable Signal. I understand VATS controls fuel injector pulse, we're 100% sure it doesn't affect fuel pump operation?

 

Hey I'm glad to try to help . The term "cranking fuel enable" is the passkey's signal to turn on the injector pulse while cranking , because the passkey module has been satisfied . I'ts an AC signal of something around 50 HZ but don't quote me on the exact frequency (something about either 30 or 50 HZ sounds familiar ?)

Another quick question , the wire at A6 that's fed from the same fuse as the passkey module is in the schematic I posted above , does it have +12V on it when the key is on ?

 

It does. I have located the main issue though!

After asking about ground location I thought "I don't recall seeing harness grounds anywhere!" So I went groping my harness looms and voila! The main ECM grounds on the RH head were not attached. I checked the LH head and they looked questionable. I tightened everything up and now I have ECM operation. The Security light comes on and goes off (WOOHOO!) and the SES light illuminates. I still did not hear the fuel pump run, so I probed A1, it was dead. I thought "probably another missed ground" so I backprobed the BLK/WHT wire on the fuel pump relay and supplied a supplemental ground. The A1 pin now supplies 12v for 2 sec, however I still do not hear a pump running. I will have to dive back in tomorrow in the sunlight to hunt for more faulty grounds. I would have loved for GM to supply which components use which grounds.



Also I've added some more diagnostic gold attachments

 

Great progress ! Last night I had thought of mentioning the grounds on the back of the cylinder heads and in my chasing of the positive side of the circuit I completely forgot them . So now you do have the relay engaging the two second prime , electrically , but no fuel pump action as I understand it . Next up is , if you do have +12V for two seconds (approximately) on the fuel pump's grey wire at KOEO , to move back to the connector under the rear seat and see that there is power there . The connector is behind the top portion of the seat (not the bottom portion where a passenger's butt goes) but I can't remember if it unplugs from there or from under the car just above the differential where it passes through the body . The idea being that if it does have two seconds of +12 all the way to that connector then the fuel pump is likely bad , an all too common failure that results in needing to drop the exhaust a bit , drop the rear axle assembly a bit (don't need to fully remove it , just things like shocks and such unbolted so as to let it hang down out of the way) and take the tank out to replace the pump .

BTW , kudos to you for taking on a project where your not only having to find and repair the original fault , but also the crap work done by someone previous that is adding more problems into the mix . I call such projects "Automotive Forensics" because of the unknown nature of what was done to it before you got to it . Once you fix all the previous mistakes and find the actual component failure that started all the ham fisted hackery on the previous owner's part it'll quite satisfying to hear it fire up

 

You are exactly correct about Automotive forensics! Even being an ASE certified Tech, with all these specialty patches. The problem is the time gap. My training revolves around OBDII and newer, working on the thirdgens makes me slow down and think a little harder. I do have access to a snap on MT2500 so I can diag the OBD1 stuff if needed, but sometimes it's just more satisfying to wrap your head around the theory instead of having a tool do it for you.

I'll be testing the remainder of the fuel pump circuit this evening after work, and noid lighting the injectors as well, just to be sure.

 

Well my noid lights say the injectors are working properly. I forgot my DVOM at work, so i didn't get the fuel pump curcuit verified. Oops.

(note:the f/p connector is under the car)

But I did fix one thing. Mechanical timing was out probably 2 teeth on the distributor. And the aftermarket timing cover they installed doesnt have a timing tab. Stupid. Found TDC the hard way. I have been told that previous owner installed a cam, I hope it's not too wild for the TBI 😞

There are just some people who shouldn't be under a hood, and I think they owned this poor 92 before me.

 

Ok verified power to fuel pump, added ground, still no operation. Sender is reading accurate though. Time for a fuel pump.

 

I'll bet the fuel pump was the problem that started all the other hackery you found and fixed already . You've got a noid pulse and spark , once it's getting fuel hopefully it'll fire right up

 

Pump will be in tomorrow. Hopefully I won't have to worry about whatever cam they put it. Turns out that's where everything went south, after the son of the owner installed a cam.......Ugh.

 

Parts came in today, late as usual. Should be working it in tomorrow.

 

Pump is in. Car has fuel. Tries to fire but rh injector is pouring fuel. Going to split the throttle body open tomorrow.

 

Ok, rebuilt the throttle body with an ACdelco kit, also modified the TBI base for better flow per the Ultimate TBI mods. I did not modify the throttle shaft.

The car will now hit and start but runs very rough, and very rich. The injector spray pattern is perfect now and is no longer leaking into the intake.

I need to verify timing, which is very difficult because of the missing timing tab, and I still have no clue what the mystery cam is.

Distributor, plugs, and wires are new. Coil pack looks old but not bulged or leaky. The plugs are E3's so they will be replaced by ACdelcos very shortly.

Anything else I should peek at?? Oh, it does have two stored codes, 33 and 42.

I will be hooking into a Snap-On MT scanner this evening to view the data, I can get whatever needed to diag from there if it will help.

Thanks for getting me through this fellas!

 

Interesting description I found when I looked up code 42 ; "Ignition Bypass Circuit Error" . I honestly have no clue what that one is , Could it maybe mean the connector that's supposed to get disconnected to set the base timing has been left disconnected ? The code 33 was listed as "MAP sensor circuit error (signal high indicating low vacuum)" , I'm left to wonder if the low vacuum situation is a result of the unknown cam ?

 

I did have the EST connector off during the paper clip test so the code 42 may very well be that. I'm going to play around with a vacuum gauge tonight and see what turns up, I think I am also going to double check the valve lash adjustment to make sure it was done correctly.

Also a side note now that it comes to mind, When cranking the engine, I have to give it a little throttle to get it to take off, and before it takes off it seems to splash a lot of fuel out of the throttle body. Do you think this could be a valve open during compression or something of the sort? A vacuum gauge should help me pin that one fast. I very much dislike wiping someone's rear end here, lol. I'm half tempted to just gut the engine and put the stock cam back in. (Unless I can get it to run, then I'll burn a PROM )

 

If it is pushing fuel back up out of the throttle body my first guess would be that yes , an intake valve is open when it shouldn't be . But with the mystery cam , all bets there are off . In fact , I'm beginning to wonder if whomever installed the cam got the cam to crank timing right , a tooth off having the cam timing retarded (late) in relation to the crank would be a possible reason for the bad running and spitting back fuel out of the TB .

PS , I hear ya , and totally respect your devotion to fixing someone's poor quality repairs . Fixing broken cars (or any broken machine really) is really straightforward , right up until someone who should be banned from holding tools has been there first , and then yes indeed it truly is "Automotive Forensics" like we mentioned earlier .

 

Code 42 is normal when the engine has been run with the EST/BYPASS connector open.

Code 33 can be set with an engine that is struggling to run. It can also be set when a ratty cam is installed. There is a calibration parameter that can be changed to prevent that code (LD472: FCB 156 ; ??.0 Kpa, BARO max limit).

Depending upon how ratty the cam is, it will also cause the engine to run rich at lower RPMs, such as idle. May also be worth the time to check the valve lash. Who knows if it was done correctly.

If you do end up replacing the cam, don't go stock. See if you can find an f-body LT1 cam, much better choice. Note that the cam gear pin will need to be shortened. Can either cut it or drive it in further.

RBob.

 

Thanks Rbob, glad you chimed in. I know you're the go to tbi guy

 

Scan tool shows MAP at 4.82v key on engine off. Applying vacuum lowers the number appropriately so i believe the MAP to be good. Still shows code 33 so MAP is doing its job. Vacuum gauge on the non ported vacuum inlet on the tbi shows erratic vacuum between 10 and 0 inches, and thats applying throttle to maintainan "idle" i believe timing is close but I have noticed lots of fuel spray out of the tbi, almost like air is pushing back out of the intake at lower rpms. The egr vacuum is disconnected and all applicable ports are plugged. Need some more direction guys

 

Im leaning towards the cam being too ratty. I'm going to pull the timing cover today, but first I'm going to manually apply vacuum to the MAP and see if cutting fuel will improve idle. Also if I haven't added this yet I have replace the E3 plugs with factory ACDelcos.

 

I know this is a very simplistic question , but I haven't seen you mention having done it in the thread ; Have you taken the valve covers off yet and determined whether the rockers are correctly adjusted ? If they are too tight it could cause the fuel you see blowing back through the TB and the low vacuum/poor running . If the valves are set right , and if the cam is properly timed to the crank , then yea it may be a case of too much cam for the engine's present build .

 

I have not yet, but i will do that before I pull the timing cover apart today.

 

Update!

I finally found time to pull the valve covers. I stick to my previous comments about some people being under the hood. It should require a license to buy tools!

/EndRant

I found at least 2 rockers almost completely bottomed out, and better than 6 rockers rattling loose. They are all cold adjusted now and my vacuum has stabilized and returned. I'm seeing between 10 - 12in around idle and 15in around 2,000 rpm. I think all that's left to do is put a timing light on it. Which is another issue, with no timing tab. Ugh. Advice? I have noted on this engine TDC appears to have the slot in the balancer at noon, instead of 2 o'clock.

Hopefully car is stable with the cam so I can datalog and get into prom burning.

Again thanks for the help fellas

 

Sweet ! I'm glad it was something easy like improperly adjusted valves , sure beats replacing the cam . With no timing tab you have three options , #1 replace the missing factory components , #2 get a degree wheel and TDC indicator to make your own timing marks , or #3 do it in a way that lots of folks disapprove of but works just fine when done right , "by ear" . With the timing plug unplugged set it to some place where the engine runs , and drive it . Does it ping (spark knock) ? Then retard it a bit till the pinging stops , and then maybe a degree or two more to take care of the pinging that you can't hear . Does it lack power and excessively heat the exhaust ? Then advance it a bit till it runs good with no pinging . It's a back and fourth adjusting/tweaking kinda thing till you zero in on the timing that the engine runs best at without pinging or lacking power , appropriately called "Giving the engine what it wants" by one of the forum's most experienced members (and no , that isn't me) .

 

With that low of a vacuum you will need to set this value higher:

LD472: FCB 156 ; 68.0 Kpa, KPa = (ADC * 0.369) + 10.415, BARO max limit

Set it at least 8 - 10 KPa higher then the idle MAP value. This is to prevent a code 33, MAP high.

RBob.