1991 ZR1 Restore - Help!

[kapkanimd]

Hi everyone,

I picked up a non-running (had known bad fuel pumps) '91 ZR1 with 56k miles on it as a project to restore.

Here is what I have done so far:
- 2 new Suburban Fuel pumps & fuel filter
- new fuel pressure regulator & injectors
- all new coils, spark plugs, & wires
- new belt and belt tensioner

- rebuilt damaged vacuum system (tested now working)
- cleaned up plenum, injector housing, throttle body, starter, etc. & replaced gaskets
- new calipers, brake hoses all around, & brake fluid (rotors were turned)
- flushed clutch fluid (no pressure when I got it)
- new K&N air filter
- replaced oil & filter, trans oil, and differential oil
- new battery

After finishing, the car cranked right up on first try. It ran rough, and would cut off randomly but would restart right away. After a few minutes, everything smoothed out and it would idle perfectly up to temperature. I did notice that the vacuum pump would now start running constantly (which was frustrating) so I new something was now leaking, but it still ran.

The next day, I started it up, ran/idled perfectly up to temperature. A few hours later, went to start it, and now it is just cranking but will not start/run! I lifted up the plenum, found & fixed the vacuum leak, and sealed it back up. Still no start!

I checked fuel pump fuses, jumped the fuel pump to hear it run, and used my MT2500 - everything checked out as normal. Next step is get a fuel pressure gauge, but not sure why fuel would all the sudden be an issue.

Any other thoughts? Things I should check? If I need to I can pull a plug to check for spark, but working on it alone and will have to wait for help.

Thank you in advance!!

[viper107]

91 cars were horrible for ecm,s going bad,they had a updated version I think they were putting in 94 ones,are the injectors new or rebuilt

[kapkanimd]

91 cars were horrible for ecm,s going bad,they had a updated version I think they were putting in 94 ones,are the injectors new or rebuilt

Brand new accel injectors.

Any way to test the ecu or determine if it?s bad? Any Tampa area ZR1 owners I can swap ecu's with to test if that's my problem?

This car also came with a Doug Rippie Motorsports chip. I just swapped it out back to the factory chip, and it didn't change anything...

[viper107]

Does it have and ecm codes? If it has alot of wierd codes or it says loss of communication it's probably the ecm

[kapkanimd]

Does it have and ecm codes? If it has alot of wierd codes or it says loss of communication it's probably the ecm

No codes at all.. when it was running no check engine light and when I ran It through the MT2500 there were no faults and everything tested fine

[viper107]

You Shure you don't have the fire order off?

[viper107]

Does it sound like it has compression? Do a compression test,fuel pressure test,and spark test

[richarde]

Has the fuel quality been checked? Could water / bad fuel be the source of the problem? My black '90 had been left outside for 8 years before I purchased it - Both fuel pumps were rusty / inoperative which I replaced along with the fuel filter and fresh fuel. I also checked both the fuel input and return lines - both contained lots of horrible sediment that would have passed straight through to the fuel rail, regulator and injectors.

[kapkanimd]

I swapped the wires one at a time so am 99.9% sure the order is correct. I will start with the fuel pressure and spark tests. The fuel tank was completely emptied and cleaned then 5 gallons of fresh premium put in. I did not specifically blow out the lines but hopefully that wouldn?t be enough to kill the New injectors.

I did notice the tach was quite off which I initially contributed to the gauge cluster common problem. However when I displayed the rpm on the HVAC screen it was matching what the tach displayed (which was going up to 9k rpm though you could clearly tell the engine wasn?t that high). I read another post on here about a non start due to failed crank sensor.. so now I?m thinking i should test/replace it.

[Z51JEFF]

Here's a long shot,check the airbag fuse. If the fuse is removed,blown the car won't start. Regardless of what it is based on your mechanical skills you will find the issue.

[Corvette95]

My 2 cents.... Sounds like you should consult a shop with Corvette (C4) experience. I would not keep trying to crank it. I would verify all the work you just performed is not part of the issue. I also agree that the plug wires could be crossed up as well I know you said you replaced them one at a time but verify with the service manual) . I would also check the DIS connections..how did you unplug and reconnect the DIS? Also, I would get a fuel pressure tester and connect to fuel rail and jump the fuel pump connector (under or around brake booster and make sure you have fuel pressure as fuel lines could have come off in the tank or similar issue) . Don't make the mistake of saying I just fixed that and assume it is all working. Any ZR-1 owner needs two things... Factory Service Manual and Tech1 scanner ( a generic OBD1 scanner will make do until you can find a Tech1 -they are getting very pricey now). The more you do to it, the more you have to recheck. VERIFY and repair... don't guess at it. Again, just my two cents.

[Young1]

Let?s back up a bit. Since you had the plenum off are you sure the connectors are all installed correctly? Two on rear and two underneath. Fully seated, latched, no pins bent. Some times mechanic hacks break the tabs.

I know you have replaced fuel system parts fine and dandy but does it have the correct fuel pressure at the rail? You may have a fuel pressure leak inside the tank.

[kapkanimd]

To clarify, the car was running and idling normal. The only issue I had while it was running is that it would bog down some with revving it up. I double checked the fuses today and did notice FP2 fuse under the dash was blown. I reinstalled a 15a one (I saw that was recommended when changing to Suburban pumps). However, that did not change anything (still won't start).

I am still waiting on the fuel pressure gauge to get here and will test that asap.

Connectors were verified as locked via their clips before I closed up the plenum, but can certainly check if any popped loose. I can also check wires (best I can without removing the plenum again just yet), but I dont that fits the best here (plus no check engine lights or codes on the MT2500)..

Thanks again for all the feedback. I did order a Crank position sensor just because it was cheap and not too difficult to change.

[Corvette95]

soooo. describe how you got the DIS wiring off and ON .

[kapkanimd]

Soooo...... realized I can just do one of the loaner tools from local auto parts store. Hooked up the gauge no reading. Jumped the pump wire (heard pumps running), but still no reading. Thought maybe just bad connection for valve, but manually activating the schrader valve (with pumps running) had minimal fuel coming out (there was no fuel coming out manually before jumping pumps).. Just to be 100% I sprayed some starting fluid in, and the car started right up... FML

So now the question is, why would I all the sudden loose fuel pressure... clogged fuel filter? The pumps are working, I guess I can pull the assembly out again to see if an internal hose came off somehow.. The fuel pressure regulator is a new retrofit from Phil on this forum, and as mentioned 2 new fuel pumps, and new fuel filter.. Granted the system was garbage before this process.. I did not replace the fuel pump assembly which had some rust on it, but seemed to be functional after a thorough cleaning (fuel gauge in car does work as well)


***I am currently following the instruction on how to test each pump at the wire harness connected to the sending unit. I will also pull the unit to see if any hoses are loose - will report back shortly



Sorry for the unnecessary rabbit hole I was leading everyone down.

[HAWAIIZR-1]

Soooo...... realized I can just do one of the loaner tools from local auto parts store. Hooked up the gauge no reading. Jumped the pump wire (heard pumps running), but still no reading. Thought maybe just bad connection for valve, but manually activating the schrader valve (with pumps running) had minimal fuel coming out (there was no fuel coming out manually before jumping pumps).. Just to be 100% I sprayed some starting fluid in, and the car started right up... FML

So now the question is, why would I all the sudden loose fuel pressure... clogged fuel filter? The pumps are working, I guess I can pull the assembly out again to see if an internal hose came off somehow.. The fuel pressure regulator is a new retrofit from Phil on this forum, and as mentioned 2 new fuel pumps, and new fuel filter.. Granted the system was garbage before this process.. I did not replace the fuel pump assembly which had some rust on it, but seemed to be functional after a thorough cleaning (fuel gauge in car does work as well)


***I am currently following the instruction on how to test each pump at the wire harness connected to the sending unit. I will also pull the unit to see if any hoses are loose - will report back shortly



Sorry for the unnecessary rabbit hole I was leading everyone down.



As Young1 mentioned you need to ensure your pumps have pressure and not losing pressure in the tank.

16798

16799

Any chance the plastic old and brittle Y connector is cracked during fuel pump replacement or otherwise? Carter200 sells the replacement piece above that a lot of folks have upgraded to. The photo mine to replace as preventative maintenance.


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[kapkanimd]

Pulled out the sending unit, hose popped off the primary fuel pump.. Connected it, and it cranked right up :) I connected the pressure gauge back up, and it is only showing about 18PSI.. No change in pressure throughout the rev range, which I do not think it is how it is supposed to work. Not sure if it is this gauge I got from O'Rileys or if something else is wrong.

However, it is still running awful when you try to add throttle. Here is a video I just recorded: https://youtu.be/JTs3TFz8c38 . Ignore the exhaust leak, I am replacing the rusty H pipe that was on it.

This car has not run in probably four years or longer. It definitely smoothes out some as it warms up. I am wondering if it will just take time to clear up. I have some valve cleaner I want to run through it, but just waiting to get the car back on the ground and out of the garage.

Also in the video you can see the tach issue I am having. I didnt hook up the OBD1 this time but will tomorrow.

[dredgeguy]

I had a similar issue and found a fuel hose hanging when I pulled the fuel pumps out to check them. Replaced the plastic clamps with stainless steel to be sure they stay in place. Wish I had also replaced the Y with Carters upgrade but that is for next time. Looks like your making progress....stay at it, you will get it up and running right.

[JG95ZR1]

Does it hold fuel pressure at all when you turn the car off ? Could be a fuel pressure regulator or a pin hole in the pick up tubes in the sending unit. One of my cars had that issue


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[JG95ZR1]

Make sure fuel filter is also installed in the right direction


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[kapkanimd]

My sending unit definitely has seen better days, but I replaced the hoses, pumps, and screens on it. There was a lot of rust so I can't rule out pin holes in the metal.. the fuel pressure regulator is new like I mentioned so I am assuming that it should be fine (hopefully).. I can start look for a new sending unit and keep trying other things as well. Fuel filter should be on correctly, but I will check again to be safe. THANKS!

[Corvette95]

18 psi? Could you have the fuel line connected in right direction or and pumps plugged up right? You have a fuel problem which is one of the more user friendly systems to check quickly. Also, since you have Phil's fuel pressure regulator, are you sure the fuel rail is connected/assembled correctly?

[kapkanimd]

I put the fuel pressure gauge right after the fuel pump/sender outlet and was still only getting 18psi. So definitely issue with the assembly. I posted a WTB and if anyone has any leads on a replacement fuel sending unit let me know. (Fuel filter is on in the right direction :) )

Also now for some reason my a/c unit in the car stopped working.. was working fine until today :(

[kapkanimd]

Sooo.. I decided while I am waiting, to finally put the wheels back on and get it on the ground and moving.. pulled it out the garage and it was clearly not driveable the way it was still stuttering (with I assume lack of fuel).. I let it run outside while I cleaned out the garage, and when I went to move it back it, it was running completely normal (normal idle, rev'd up with out stuttering, etc.)!

So I took it for it's first drive in years! Got back and started airing up the tires and then randomly I could hear the idle drop and it started running rough again :( Got it and it was back to the way it was where it was stuttering and undriveable.. It through a SEL which was Right O2 Sensor too Lean, which I checked values and it was randomly showing 0mV..

So now I am thinking it may not be the sending unit after all... Any thoughts? could it be the 02 sensor this whole time? relay? ecu? I guess I could start with 02 sensors.. I was thinking of doing headers anyway..

Either way, happy to see this thing moving on it's own power for the first time in years :)

[viper107]

If it's acting possessed,put in a few new gm o2 sensor's,they need it anyway,if still persistent,I say ecm

[kapkanimd]

I swear this car will be the death of me..

Yesterday I put the hood back on, started it up to check the lights, and now I am getting a battery light on... drove it today to the gas station and back and am only getting 11.4v per the computer.... The only other thing different is that I left the trickle charger leads on the battery (not plugged in) when I started it.. I keep reading about fusable links on this car but seems like no one really can identify it.. I am hoping it is not the alternator, any thoughts? When I get time I will get a meter out and start testing what I can. I see a lot of instructions for regular C4s.. is it the same for the ZR1?

Today I changed out the 02 sensor before driving it, and the data from the computer looks normal now, but it didnt really change the way it was running like I would have hoped. However, now I am throwing another code:31 (Cam sensor diagnostic error)..

I was reading another thread on here: http://zr1.net/forum/showthread.php?t=25747 that was getting similar symptoms to me (my car does not like to start when warm/hot, I have to wait until it cools down and then it fires up on the first try. I also get random stalls when starting - cranks up idles high then when it drops it just goes straight to stall. This goes away usually after it gets warmer/runs for a bit)

I can test the cam sensor, and it was also mentioned that I could be chasing phantom things that is being caused by the ECU... I have been throwing money at this thing like water, and am just trying to get it reliable at this point... I am over the budget I was expecting to get this thing going and i havent even made it to the body/paint shop..

[Young1]

The cam sensor code 31 can cause intermittent stalling and restarts. The only replacement is one built by Jagpanzer here on the forum. I have been running Jagpanzers prototype for I think four years now. Cam sensor does not exist NOS, unless a forum member lets go of one stored on a shelf. Be patient, these cars are reliable fun once all the 30 year old parts are replaced.

Plugs, wires, coils, injectors, vaccuum valves, clean up starter solenoid, vacuum pump, cam sensor, O2 sensors, fuel pumps.

Either nickel dime it or do it all at once and be reliable.

I would not hesitate to drive mine to the west coast at this moment.

[kapkanimd]

Small update: I have since replaced the fuel sending unit, swapped out the pumps for two new ones under warranty, the second 02 sensor, buttoned up the exhaust, and today changed the alternator..

Car runs a lot better, but still not right.. I am still getting the SEL as soon as the car gets hot and it is throwing the cam positions sensor code again. then once I turn off it will no longer start until it cools down completely..

I messaged Jagpanzer (who I also got the new fuel pressure regulator from) to see if he is still doing the cam sensors.. Not sure what else I have left to try..

[Young1]

Replace the crank position sensor. Car will not start if it is bad. Most likely the sensor gives bad signal when hot. They are readily available. The car does not need the camshaft sensor to start but to increase timing accuracy. I left mine unplugged one time is how I know.
You will need to grind it to fit into the recess in the block. Also apply some RTV to keep the oil in for good measure.
PM me with your phone number and I can talk you through some stuff. I have a daughter on the north side of Tampa too.

[kapkanimd]

Replaced the crank sensor, no change. Replaced the cam sensor, no change....

today, I checked the the injector relays and injector resistance, all checked out good

All that is left is the ECU or the fuel pumps themselves (which are both new - advance auto suburban pumps).. I am going to grab the fuel pressure gauge again and start testing everything per the manual..

The sad thing is, I have found a TON of threads on here and other forums mentioning the exact same problems an no one ever comes back and updates their solution...

Current Major Issues remaining:
1. Anything but minor throttle input will bog the car down. I can only slowly accelerate smoothly with small throttle input. If I push harder it just putters...
2. Once the car gets to temperature (higher range) the car starts running very rough, will eventually die, and will not restart until cooled off significantly (hours later)

If everything with trouble shooting the fuel system checks out, I will pick up an ECU if I can find one.. I did take mine out, clean it, and reinstall with no change...

[kapkanimd]

Did some more testing today...

Both pumps are working, but I am still only getting 18-20psi fuel pressure... on top of that if I pinch off of the return fuel line, there is no change in pressure..

As mentioned the pumps are new Advance Auto (Car Quest) E219663 pumps from a same year 7.4L Suburban.. Which I am now realizing might just be the wrong pumps.... I just ordered new GM ones (EP381).. Hopefully that helps the fuel pressure issue..



Also discovered some lovely coolant under the passenger side dash.. I am guessing from when I used the heater to test it.. fml...

[kapkanimd]

Update! New pumps in, car is running normal now! Finally!

However, I got it up to temp (no issues) then let it sit for a bit. When I started I got the dang 31 Cam sensor code again. The car didn?t run as rough as it used to with the SEL light and actually restarted, so still in a better place? I?ve tried 3 different cam sensors so I?m guessing it still might be a ecm issue.. I?ll run some more tests, but overall happy..

Coolant leak: I tried a new cap but still leaking.. I think it might just be corrosion at the inlet and I need a new tank.. anyone see this before?

[GOLDCYLON]

Update! New pumps in, car is running normal now! Finally!

However, I got it up to temp (no issues) then let it sit for a bit. When I started I got the dang 31 Cam sensor code again. The car didn?t run as rough as it used to with the SEL light and actually restarted, so still in a better place? I?ve tried 3 different cam sensors so I?m guessing it still might be a ecm issue.. I?ll run some more tests, but overall happy..

Coolant leak: I tried a new cap but still leaking.. I think it might just be corrosion at the inlet and I need a new tank.. anyone see this before?

No but that tank is not ZR-1 specific and on the entire C4 run. So that's some better news. GC.

[jss06c6]

Update! New pumps in, car is running normal now! Finally!

However, I got it up to temp (no issues) then let it sit for a bit. When I started I got the dang 31 Cam sensor code again. The car didn?t run as rough as it used to with the SEL light and actually restarted, so still in a better place? I?ve tried 3 different cam sensors so I?m guessing it still might be a ecm issue.. I?ll run some more tests, but overall happy..

Coolant leak: I tried a new cap but still leaking.. I think it might just be corrosion at the inlet and I need a new tank.. anyone see this before?Looks like the upper pipe nipple that is (I believe) soldered is leaking. See if it moves when you remove the hose and wiggle the pipe. If so, you might be able to remove the tank, clean and dry it and resolder the pipe nipple to the tank. Challenge will be to get the fluid out of the fractured joint so that you can effect a good repair. Absent that, it the same as the LT-1/LT-4, so you should be able to locate a good replacement.

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[kapkanimd]

Quick update:
-Replaced the clutch master cylinder and slave cylinder (was leaking bad in bell housing)
-Replaced the coolant reservoir (however I think the heater core might still be leaking)
-Dropped oil pain, cleaned everything up, and put new gasket

Now no leaks at all and car is still running great. It is now giving me issues starting where it is just clicking.. I think it is the switch :( it never did this before changing out the master cylinder..

Still left to do:
-Suspension: bushings, tie rod ends, and shocks
-Radio not working (shows the stuck time of 1:00, no sound, and no antenna)
-A/C not working (clutch not coming on)
-Paint needs fixed (clear coat missing on hood and other areas)
-Replace all the weather stripping

Turning into a long project, but hopefully worth it in the end

[viper107]

Cam codes are probably due to misfire,are the injectors fat body type or plastic skinnys,I would definitely get a 94 or 95 ecm because the 91 ecm is junk from new

[spork2367]

I would definitely get a 94 or 95 ecm because the 91 ecm is junk from new

Can you elaborate on this?

[viper107]

every 91 i have had (years ago) the ecm went south on low mile cars (3) and back then i believe around year 97-98 they updated the part number to the later year part number/plug and play ac delco i bought them whole sale for under 200.00 brand new

[kapkanimd]

every 91 i have had (years ago) the ecm went south on low mile cars (3) and back then i believe around year 97-98 they updated the part number to the later year part number/plug and play ac delco i bought them whole sale for under 200.00 brand new

Do you have the part number and a source to get it?

[spork2367]

every 91 i have had (years ago) the ecm went south on low mile cars (3) and back then i believe around year 97-98 they updated the part number to the later year part number/plug and play ac delco i bought them whole sale for under 200.00 brand new

I've never seen this posted anywhere but in this forum by you. That I'm aware of there is nothing particular to the 91 ecm that would support this statement.

Do you have the part number and a source to get it?

They are only available on the used market.

[ZR1CK]

Hey kapkanimd, your motor sounds just like mine when I was having the same issue and a code 31. I went through several test procedures, not all that you have, but according to the 1991 Service Manual. Which is by the way, a very important tool to have. And ended up with a faulty ECM. Sent it off to Marc, he fixed it, and then the motor ran as it suppose to. Good luck with yours and hope you correct it before it drives you crazy...cuz it can.

[george1945]

Had a very Similar issue with our 90 ZR-1. went thru it all as you did. Replaced the fuel pumps and still no run. Pulled the crank Position sensor and replaced with a unit recommended by Mark and it now runs perfectly.