Engine 92 LX Won't fire - seems like a fuel delivery problem

vferrizz

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Oct 23, 2020
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Been searching previous threads and am kina running low on ideas so I could use some re-directing. Short history: car is a '92 LX with a bone stock 5.0 motor and a Tremec TKO 600 that took the place of the AOD. She started running a little crappy in that I was hearing some popping in the exhaust and the car would idle a bit rough after about a minute after giving the car some gas. I cleaned the MAF and re-set the timing to 14 deg (was set around 20 deg) and nothing changed. A couple weeks later the car would stall the first time I would start her up. Once I tried again she started fine. About 2 weeks ago I started the car and as I backed out of the garage the car stalled as soon as I gave it some gas. I have not been able to start the car since. I ran the codes and got 15, 67 and 96. I assume I got 67 because the clutch was not in when I ran the codes (Key on, car off). The 15 bothers me a bit but I have not dug into that one much yet. As for 96, I replaced the fuel pump relay and no change. I checked the fuel pressure and I have 38 psi. The car turns over fine and is trying to start so it seems like a fuel delivery problem. I am going to try replacing the fuel filter next, hoping it is that simple. But, the 15 and 96 codes seem to tell me I have a bigger issue. Not sure which way to go next so please help give me a clue!

Thanks
 
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KRUISR

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Do you hear the fuel pump hum when you turn key to run (key on, engine off)?

Follow the checklist.

Also could be a bad TFI module, it would give the stumble and popping (aka - misfire).
 

vferrizz

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Thanks for the reply. Time to hit the list. I will also look into the TFI module. Times like this is when I miss carbs...I understand those at least.
 

KRUISR

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But when it is working right EFI vs carb... not even in the ballpark as far as driveability.
 
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vferrizz

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Makes sense. I am sure it is the original FPR. Car had 26k original mikes on it when I got it in 2018 so I am sure some of the original equipment is getting tired. Thx.
 

vferrizz

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I was going thru the checklist and was checking for spark. I hooked up a tester to #5 cylinder. While cranking the tester flickered constantly but got bright periodically. I thought what I should have seen is the light flash only when #5 got a spark. I think when it got bright is when it was getting spark but shouldn’t the light have been completely out before it gets spark?
 

jrichker

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I was going thru the checklist and was checking for spark. I hooked up a tester to #5 cylinder. While cranking the tester flickered constantly but got bright periodically. I thought what I should have seen is the light flash only when #5 got a spark. I think when it got bright is when it was getting spark but shouldn’t the light have been completely out before it gets spark?
What kind of spark tester were you using?
 

vferrizz

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I picked up one at Autozone. It’s the kind you plug in series with the spark plug wire and the spark plug. Based on some other feedback I did replace the TFI module and got the car to start and run for a very brief time. Initially it seemed fine but then started bucking while I was driving. I only had about 32 lbs of fuel pressure at idle but I forgot to disconnect the vacuum line before I checked it. Now the car starts and dies right away so I have to get it running long enough to recheck the pressure. This is turning into a huge PITA.
 

Kid wita 5oh

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I was going thru the checklist and was checking for spark. I hooked up a tester to #5 cylinder. While cranking the tester flickered constantly but got bright periodically. I thought what I should have seen is the light flash only when #5 got a spark. I think when it got bright is when it was getting spark but shouldn’t the light have been completely out before it gets spark?

Have you looked under the distributor cap?.....sounds like it may be arcing in there
 

7991LXnSHO

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But when it is working right EFI vs carb... not even in the ballpark as far as driveability.
Then you do not know carbs well. EFI is better for emissions and precision tuning, but a carb will have fine drive ability even if it is a bit rich or lean.
 

vferrizz

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Update.....
Been getting my a** kicked on this since last spring. I will spare all the painful details on what I have checked, computer codes received and parts replaced. The computer codes have not made much sense and seem to change for no real reason. Here is a short current summary: Car is still extremely hard to start. Turns over fine, wants to fire but struggles to fire. Once I finally get the car running, I have spark to all cylinders, fuel pressure is 40 psi, TFI module is new, distributor is new, TPS is 0.79 VDC at idle and is smooth up to 4.99 VDC at full throttle, base timing is set, idle is set (did this since I finally got the car to run yesterday). Also removed and cleaned the IAC and EGR.

Now I only have have engine running error codes 72, 2 and 1 (the 2 and 1 make no sense). Car idles OK at about 750 RPM but when I hit the gas it sputters and wants to stall. If I push the gas slowly it gets up to 3000 RPMs then starts to sputter. Here is the weird thing, if I keep the clutch pedal depressed the car idles smoothly and when I hit the gas with the clutch pedal in fully the car runs smoothly up to to 5000 RPMs. Looking at the wiring diagrams I see that the clutch pedal switch inputs to the starter circuit but also inputs to the ECM. Anybody know why the ECM needs to see if the clutch is in? More importantly, any idea what the heck I should do next??? Thanks in advance.
 

vferrizz

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I pulled the computer and had it serviced since the error codes I was getting were so random I thought maybe the ECM was the problem. The only change since I had the ECM done was now I just get the codes 72, 2 and 1. When I pulled the spout the timing retarded a bit and I set the timing to 12 deg. Once I put the spout back in the timing advanced a few deg.
 

7991LXnSHO

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I pulled the computer and had it serviced since the error codes I was getting were so random I thought maybe the ECM was the problem. The only change since I had the ECM done was now I just get the codes 72, 2 and 1. When I pulled the spout the timing retarded a bit and I set the timing to 12 deg. Once I put the spout back in the timing advanced a few deg.
Random and changing codes is a sign of the ECU needing serviced or demonic possession. High five.
The single digit codes concern me.
 

vferrizz

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Random and changing codes is a sign of the ECU needing serviced or demonic possession. High five.
The single digit codes concern me.
Yeah, single digit codes threw me off too. The last engine running test I got the following: when the number of cylinders was displayed, it showed “0” instead of “8”. Then during the test I got codes 72, 2, 72, 1. I am losing my freakin’ mind over this.