When she runs she runs great. But she might start 20+ times then all the sudden it wont start.Sometimes starting fluid will work and other times it wont. Now it will sit and idle for 10-15 min and just shut off like you shut the key off.I have noticed the when the fans kick on it will hesitate.So far Ive replaced plugs,plug wires,fuel filter,fuel pump,coil,dist cap,rotor,pick up coil,icm,then a whole new dist.,the computer,and finally the injecters.Ive chkd all grounds,40 lbs fuel pres.while cranking and holds pressure for quite awhile. After replacing the inject it ran for a week,when I pulled into my drive and it just shut off.Im to the point of getting rid of this piece of sh*t,lol. Anyone got any ideas?

 

When it just "shuts off", do you still have electrical power in the car? Interior lights and all that still work? Headlights work, cranks? When it loses power and just cranks, do you have spark? I'm assuming not, but it's worth checking.

Check the cable connections on the battery and starter. Also make sure the wires are good on the solenoid.

It really sounds like you've got a loose wire that works "most" of the time, but then vibrates loose during driving and loses it's connection killing the motor and power.

 

I replaced the solenoid on the starter and the wiring was fine. There is also pwr to everything else after it dies. Yes,it has spark while cranking.I replace the battery and the ends were fine.Ive also repetedly chkd wiring on about everything to no avail.Also,Im not just some backyard mech., Ive been working on cars for over 30 yr. and owned my own shop.But this car has me stumped!!!

 

Have you looked at the ignition switch at the base of the steering column. This is not the key part but on the other end of the rod that the key pushes on.

 

Good point Edwardgp. The way he's describing what's happening, I'm fairly certain it's a loose wire/ground that's killing it. Not too many things that would cause it just to "die" in the middle of running other than inturrupted power. Shorted out coil maybe?

 

Also, look at the fuse and the fuse holder by the battery. This is the FI/Fuel pump fuse.It powers the ECM and the fuel pump. If it goes open, the car will shut down. You will still have spark while cranking but no injector pulse or fuel pressure.

 

This problem has been going on for over 5 yr,the car will start say 50 times then all the sudden it wont. I might try it severa times and all the sudden it will start. I will chik out the ign switch. And have already changed the vats system in the column,as thats what I thought the problem was. Also I have put in 3 diff. coils and all the wiring at the coil is fine. And as Ive aready said all the wiring and grounds have been chkd numerous times. Ive been wodering if there could be a relay or a sensor somewhere thats bad. This car is not a daily driver,it sat for about 9 yr and thats when the problem first started. It Was ran and driven once in awhile. I finally got it back about 4 yr ago and have been screwing with it in my spare time ever since.

 

Ok...so you say you have spark. Then it would seem it's down to fuel.

Is there proper fuel pressure when it won't start?

Are there injector pulses when it won't start?

Can you get hold of a factory service manual? The fault troubleshooting trees are pretty comprehensive...

 

Havey ou checked/replaced the oil pressure sensor? I know that if those go bad, the car won't start also. Could be yours has an intermittent fault.

 

If the oil switch goes I think it'll start but won't stay running. Don't quote me as absolute but I think a relay runs the pump for a while, long enough for oil pressure to rise and close the switch.

So, if that's true, it makes sense why the engine might die, but I'd think it'd restart and run for a short time, whatever the timeout is on the start cycle for the fuel pump.

 

I believe the ECM still runs the fuel pump when the oil switch is unplugged. It recieves a signal from the distributer telling it that its cranking. Now if I remember correctly, my car would run but not run well when my oil switch came unplugged once. Cause I remember having to pull over and check things under the hood. I know I plugged that in and I cant remember if I did anything else to fix it but it ran fine after that.

 

Maybe one of the experts will chime in but the way it looks to me is the ECM runs the fuel pump relay and monitors the fuel pump voltage, but doesn't actually supply the power to run the pump. That appears to be done through the fuel pump relay on start and through the oil pressure switch for running.

 

was there any codes stored in the ecm

 

I believe the ECM sends power to the pump for priming and then the relay provides power to the pump after the initial prime. The oil pressure sending unit acts as a second source of power in case the relay fails and will power the pump once a couple lbs of oil pressure are detected..Although it is a second source, it couldn't hurt checking it. I had a faulty connection at mine that was causing the same intermittent problem as yours. But, if the pump relay is good then the issue should lie elsewhere, as the opsu is not the main source of power for the pump.

 

There are no codes.The fuel press. is ifine,its firing,the inj are new,ohm to specs,Im going to go aheand and replave the ops and see what happens. The strange thing is it hasnt started in over 3 mo even with starting fluid. But one of these times it will just start and will strart several times after,then it will just die.

 

Have you tried replacing the fuel pump relay yet? I had the exact same problem. It would start on occasion and do more or less whatever it wanted in terms of staying running. My problem was a loose connection to the opsu BUT it was a related problem because of a bad fuel pump relay. The opsu being loose was only a symptom of the real problem.

This is atleast the way I understand it, being the opsu should power the pump when the relay goes bad BUT the relay should still work if the opsu is bad. I know Sofakingdom explained it very well in another post I just can't find it at the moment.

 

The relay is only for a couple seconds on start. The ECM runs the relay, the relay runs the fuel pump (on starting/for a few seconds) This is why you can hear the pump run for a few seconds at key on but then it stops. The oil switch is the primary source when the engine is running.

The fuel pump relay on my car went out. The symptom was hard starting...had to crank longer than normal but it would start and run fine once oil pressure built up sufficiently (>5psi, or something like that).

 

duplicate cleaned up

 

Im going to just change both the OPSU and the FPR this wkend and see what happens.I also ordered a factory svc manual.

 

From what i've read and experienced personally, yes the fuel pump relay does prime the pump but it also powers the pump continuously after the initial prime until 3 seconds after the last reference pulse is received from the distributor, in other words as long as the car is running. The OPSU runs parallel with the relay to continue powering the pump in case the relay fails. So, technically it will run just fine without the op switch even installed as long as the fuel pump relay is properly powering the pump. This was taken directly from one of the mods posts.

Whoareu99, if you think about your fuel problem that you mentioned in example, like you said your relay went bad which caused a hard start. The system was using the OPSU for power not because it is the primary source of power but because the primary source (relay) was not providing power.

Whtlng89, if I were you, I would replace the relay first. If for no other reason, I would because it's way cheaper than the op switch. Good luck man!

 

Good plan. If it's the GM factory one they have lots of really nice fault troubleshooting trees in them.

 

With all due respect to the Mod's writings and you, I disagree.

Without having the ability at the moment to scan in the diagnostic steps from the GM/OEM service manual (relative to the 1991 model year and 5.0 and 5.7 TPI), you'll have to bear with my textual excerpt from it.

• Engine idling at normal operating temperature
• Oil pressure normal
• Disconnect fuel pump relay
• Engine should continue to run
• Does it?

If the answer is "YES", it goes on to additional troubleshooting steps.

If the answer is "NO", the diagnosis is "Faulty oil pressure switch".

This clearly indicates the OPS is the only source of power to the fuel pump while running normally.

The relevance of the ICM pulses is not to tell the ECM to fire the relay or in any way to power the fuel pump circuit, but for the ECM to decide if code 54 should be set or not set when low voltage is detected on the fuel pump power circuit. In a nutshell, if there are ICM pulses and low voltage is detected then set the code because we would expect ~12V at the pump when the engine is running. However, if there are no pulses then don't set the code because we don't expect the pump to be getting power if the engine isn't running.

 

I wish I had a copy of the diagnostic...I'm not trying to disagree with the information but the way that I interpreted it is different. Although that is the correct diagnosis for a bad OPS, it does not indicate that it is the ONLY source of power to the pump but to me at least indicates that it is A source of power. Disconnecting the Fuel pump relay, with a properly working OPS, the car should stay running. But, disconnecting the OPS while keeping the fuel pump relay intact and assuming that it is functioning, the car should still be able to run normally. I think that the excerpt from above is the correct procedure to diagnose a faulty OPS but I do not think that it justifies it being the only source of fuel pump power.

If those diagnostics are handy though man, and you have the ability to scan them in, I would love to see some more. I'm very open to adjusting my interpretation!

 

OK, I see what you mean and agree. With the FPR removed the OPS is the only possible source of power so it doesn't exclude the FPR from being one when it's in the circuit.

It would seem a pretty easy way to confirm one way or another would be to measure the fuel pump test terminal (FPTT) voltage. If the FPR is energized during normal operation (and assuming the FPR is not broken) then there should not be ~12V at the FPTT. If the FPR is not energized then you should see ~12V because the the normally closed contact of the FPR will "backfeed" the FPTT from the OPS circuit.

 

Well I picked up the OPS and FPR today. And at the risk of sounding stupid,where is the OPSwitch located? I can find the OPSU on the front of the block but so far havent found the OPSwitch. And they arent the same. My haynes manual is basicly worthless. Hope the GM serv. manual gets here soon.

 

Look toward the driver side firewall. It should be mounted near the distributor.

 

If its on the drv side by the dizzy I sure dont see it. Im going to raise it up and chk by the oil filter.

 

The earlier style units were down on the side of the block, right above the filter. On the later units, they combined the OPS with the gauge sending unit. You can tell if yours is the later style by the style of your sending unit. The later combined OPS/sending units were a cylinder about 1.25" diameter and 2" long and took an oval shaped black plastic connector with 3 or 4 wires. The early style will be larger around (about 1.75") and have a single wire connector. On the later style, there will nothing but a pipe plug above the filter. The sending unit is below and to the driver's side of the distributor. Very hard to see on the TPI motors with the dist cover in place.

 

Well,I changed the OPS and FPS and nothing happened.It does sound like the fuel pump is working better. Now its not firing again.I have pwr to the dist.and thats as far as I got yesterday. Im tryting to find the tach wire for the next test. The coil is new and I already replaced the dist. even tho it already had a new one in it. This is really getting old.

 

On my 91, the tach lead is the white wire in the gray plug on the coil.

 

Have you checked your timing? If the initial timing is off it has issues starting. Also I have seen a severly stretched out timing chain cause issues. If it is a fuel related electrical or mechanical you should be able to see this in the fuel pressure. It should never drop below 40 psi. If it is ignition related you should be able to see this with a timing light. At idle I believe it should hold a steady 20 degrees when warm at idle.

 

The car only has 84k miles on it,so I dont think the timing chain is it. Besides,when it does run it runs perfect.The fuel pres is just fine. And I have already chgd the fuel pump and filter. But if and when I get it running again I will chk the timing.

 

The fuel pressure even with just the key on will tell you if the FP relay is giving you fits. The timing chain will mostly effect starting once running usually it it not a big problem decel is just a little burbly. The only ECM related piece that would keep it from starting are the ignition pickup in the distributor and the ignition module. You said you changed the distributor. The other would be vats, but you said you changed that out. The MAP and TPS sensor may make it difficult to start , but usually it will run just very rich or lean and once you got it running it would run poorly which you said it runs great. The rest of the sensors besides oil pressure are temp related, and affect variou enrichment parameter, but usually will not effect starting. The O2 sensor will not effect starting as it is open loop when it starts.

 

Just spent the last 7 hr and gotten no where.lol Its still not firing.I have pwr to the dizzy, had the ICM tested and its fine,I couldnt get a reading I liked on the coil so went ahead and put a new one in (even tho it was already new).I cant believe its the pick up coil as I never got a chance to drv it except around town after installing the new dizzy. But since I picked one up when I got the coil,I guess thats next. And I dont think I put 50 miles on the car after the injecters were installed and drove it daily for a week and never had a problem.Then I came home after work one nite and it died in the drive. It has only started once since then, 4-5 mo ago.It ran for about 15 min and then just died like you shut the key off. I do have a code 33 now,but am pretty sure its because I tried to start it w/out a vac hose hooked up.Will clear the codes and see what happens. My BIG question is how can TWO new dizzys go bad?????

 

Is the timing light flashing as you turn it over?

 

I thought you were getting a GM service manual?

Hate to sound rude, but perhaps it would be wise to stop throwing parts at it and wait for that service manual.

 

I have the service manual thats why I had the ICM checked,and rechecked the coil,and according to the manual,the pickup coil is bad. Now my question is,WHY have two new dizzys went bad?

 

Disregard.

 

disregard

 

The pickup coil resistance is out of spec, or it's shorted to ground, or?

 

I can't tell you how many "new" out of the box equipment pieces I have that are bad and have to be returned. You could have gotten two bad ones. Maybe they were built during the playoffs by distracted employees?

 

There was no resistance in the p/up coil. Replaced and it started right up.After chkg the timing and taking it for a test drv it ran exelent. The two dizzys were bought a few years apart but the car was seldom driven. The 2nd one I dont think I put 100 miles on it. I to have had a few "new" parts that were junk right out of the box. Thats what we get for everything made in China,among other lousy countries. Now I have codes 15-33-42 which I have NEVER had any codes during this whole deal. Anyone have any suggestions to maybe speed things up a little?

 

Coolant temp (code 15) and MAP sensor (code 33) share a common ground to the ECM and EST (code 42) is or can be driven by grounding issues.

I'd probably starting checking all the harness and battery grounds to be sure they're present and clean.

It is also possible that bad grounds could be the reason for some of these failures. If the normal grounds aren't present or are poor connections, current will try to seek a better path and if that better path happens to be through items not intended to pass current (or at least more than normal current), they can burn up or cause really weird stuff to happen.

 

All three codes are gone since I plugged the coolant and maf back in.lol Its running for the time being, but this has happened several times in the last 3 yr. It will run for awhile and then out of nowhere it will just die. Time will tell.Thanks for the help everyone!!!

 

Wow I've been silently following this "ordeal" and I'm glad you finally got it running.

 

The quality standard that has to be met is a joke now! I had a brand new Accel distributor that came with a coil and it too was absolute junk...Long story short, I'm glad you figured out your issue man.

 

You'll get code 42 anytime you have the EST timing connector disconnected to set timing. There are ways to get away from the funky GM pickup coil. Both MSD and ACCEL make performance distributors that are plug and play to the GM EST system and which use alternative pick up designs. My ACCEL Billetech dist uses an early Ford style reluctor ring with a simple magnetic pick up. To eliminate ICM failures, I run an MSD Digital 6 which uses the ICM's coil drive as a PIP with very little current load. This makes the ICM's work load very light and allows it to live a long easy life. The Dig 6 drives the coil using high power drivers that, properly applied and installed, will last for many years. The MSD and other performance ignitions also provide much higher KV and spark current which is of real value in highly modified, high horsepower engines.
Many HEI dists go the life of the vehicle without failure but the HEI dist is still a huge failure item in these engines.