1994 5.7 TBI

[Fleetmon]

1994 C1500 Silverado pick-up. 5.7 TBI, auto, 88k miles, Jasper engine at 65k miles, grandsons truck.

Truck was delivered to me running (barely) very rough, backfiring through the intake, will hardly idle. Stalls when trying to take off.

New MAP and coolant sensor (CTS - near thermostat housing). MAP is working....5 volts at plug, grounded through ECM, voltage drops at middle wire when applying vacuum. CTS drops idle and picks back up when CTS is unplugged.

It acts like an engine way out of time but moving the distributer by hand doesn't seem to make much difference either.....advancing timing allows it to idle somewhat but the engine won't re-start once shut off. When running, fuel pressure is around 70psi. I'm tempted to check the cam-to-crank timing....thoughts?

Compression at #1 is 90psi......Horror Freight comp gauge is now stuck in the plug hole (the hose is turning but no love at the adapter). I suspect other cylinders are low as well. I'll have to get intimate with it to get the adapter out.

When idling, exhaust manifold temps are all averaging around 400'F except for #'s 1 and 7....they are only running around 225'F. The convertor is running about 400'F in and 300'F out. No rattling when rapping on the convertor shell.

I didn't have much time to look at it last night once the truck arrived and got disgusted with the comp tester so I'll get back on it this evening.

Any ideas? Thanks in advance for any ideas/suggestions/fixes!

 

[mattd]

by the compression something definitely wrong. With a fairly new engine, and your symptoms, i'd def check cam/crank timing.

 

[EricG]

70PSI fuel pressure is way high for a TBI. I dont think thats the problem, but normally it should run between 11-13 PSI with a TBI!

 

[Fleetmon]

really....wow....I must have read the gauge wrong or something! No doubt I looked at it wrong.

I think I'll check the cam timing next. It's hard to troubleshoot since it won't stay running long enough.....I have NO idea how he made it 72 miles to may place.

 

[Gabe]

Sounds like you need to reset the timing.

There is a black fuse panel cover on the passenger firewall - remove it. Next you need to find the brown wire with a black stripe; trace it 12" to the connector and unplug it.

Set the timing with a timing light. You might need a custom bent 9/16 wrench for this. When you have the timing set perfectly (zero degrees), tighten the distributor bolt back down.

Plug the connector back in and replace the cover.

Drive for 10-15 minutes so the idle can be relearned.

 

[cchase]

I'd seriously check the timing. How are you moving the distributor by hand? Doing this without the timing advance disconnected is a waste of time, even if you actually did loosen the hold-down bolt and aren't just somehow mangling the cap.

90 psi sounds low to me, but if they're all even I don't think it would cause a poor idle.

 

[Donald]

Wow - someone managed to ruin this durable engine in 65K miles? This should be the heavy duty version with a 4 bolt main. And it needed a Jasper reman? Now 23K miles latter its barely running? It has a timing chain, so hard to imagine it got messed up in 23K miles. Engine would have come setup properly by Jasper. While the dist. might need to be adjusted (as mentioned in some posts) that would not effect the low compression.

The vehicle probably has an in tank GM fuel pump. I was on my 4th when I sold my 1993 Suburban with 5.7L TBI. Never never run out or very low on gas.

 

[mattd]

dont bother checking ignition timing before checking cam timing. Ignition timing has nothing to do with compression.

OTOH, the cylinders could be fuel washed from flooding, causing a false low reading.

What i would do first is put cyl 1 to TDC compression. Pull distributor, install it correctly. Set timing with light and go from there.

Fuel pressure does sound high BTW. Double check it.

 

[Fleetmon]

Yep....first driver drove with no oil and the rear cam bearing spun. This is another driver (his late grandfathers truck)in the truck now.

I'll check the timing before doing anything else....the engine has been performing perfectly since we installed it in 2009 and he said that one morning on the way to school two weeks ago it just bogged down and started backfiring and etc (said gauges were reading normally). It is barely running at this point and will not pull itself around now. Like said, I have no idea how he made it the distance to my house....72 miles of beltway and then nothing but hills and curves.

I appreciate the help folks and I'll concentrate on the ignition timing first....I was worried the cam timing may have jumped a tooth or two but I'm probably just overreacting. I was thinking cam timing due to the low compression. I know more than one bank is affected and probably multiple cylinders since removing a plug wire makes very little, if any, difference in performance.

I imagine, being a poor college student, that this truck has been driven low on fuel more than a couple of times. I'll have to check F/Pressure again since I got a bad read yesterday. Luckily it's a pick-up so the pump is pretty easy to get to.

I haven't been able to spend much time on this since it arrived late yesterday but will dig into it this evening and this weekend.

 

[Fleetmon]

will do fellers.

Easy enough to do to knock out both issues....check cam timimg and reset the distributer. He had a neighbor look at it but doesn't know what the neighbor did, if anything (??).

Good point about the cylinder wash mattd....I had that happen to our BMW once.

 

[Donald]

Originally Posted By: Fleetmon
Yep....first driver drove with no oil and the rear cam bearing spun. This is another driver (his late grandfathers truck)in the truck now.

I'll check the timing before doing anything else....the engine has been performing perfectly since we installed it in 2009 and he said that one morning on the way to school two weeks ago it just bogged down and started backfiring and etc (said gauges were reading normally). It is barely running at this point and will not pull itself around now. Like said, I have no idea how he made it the distance to my house....72 miles of beltway and then nothing but hills and curves.

I appreciate the help folks and I'll concentrate on the ignition timing first....I was worried the cam timing may have jumped a tooth or two but I'm probably just overreacting. I was thinking cam timing due to the low compression. I know more than one bank is affected and probably multiple cylinders since removing a plug wire makes very little, if any, difference in performance.

I imagine, being a poor college student, that this truck has been driven low on fuel more than a couple of times. I'll have to check F/Pressure again since I got a bad read yesterday. Luckily it's a pick-up so the pump is pretty easy to get to.

I haven't been able to spend much time on this since it arrived late yesterday but will dig into it this evening and this weekend.





If all I read of your post was that it was bogging down, I would say fuel filter. Its probably a large in-line one under the vehicle. They have a habit of rusting and being difficult to remove. Don't confuse fuel pressure with volume. Now is not too early to start spraying PB Blaster on the fuel filter area even if you do not change it for awhile.

 

[The_Eric]

You probably looked at the kpa (kilapascals) part of the gauge, which correlates to 10psi. That's on the low end, you may want to double check with another gauge (preferably a low range gauge) to confirm accuracy.

We had one that read 10psi on our 0-100 psi gauge, but would still act up. After checking with another gauge, we found it to be about 8-9 psi - not enough.

 

[meep]

this SCREAMS cracked distributor rotor to me (anyone own any late 80s hondas?) EXACT behavior (ignoring compression). If if the dizzy didn't spin, then I'd change cap/rotor first. I'd gotta be throwing some kind of code as well, though with obd 1 it may not be as specific.

I'd hate to think cam timing... it's awfully young to jump the chain.

 

[Fleetmon]

Ok, Update: I checked and reset the ignition timing with the tan/blk stripe wire disconnected. With the wire disconnected the truck fires up although still idling rough: Once I hook the wire back up, it's tough to start and begins backfiring and popping:

I squirted a little oil into each cylinder and the comp raised up to 120 in #1 as opposed to 90 the other day.

Would the spark module now be suspect?

 

[crazy8]

1st check inside the distributor cap for moisture, carbon tracking or cracks all of these will cause poor running, your problem screams ignition problem. It also could be a bad module or pick up unit but before changing them I would take it to a shop and have them put it on a scope, that will tell you if it is ignition or not. As far a timing jumping on a 5.7 I have never in 40 years seen it happen. HTH

 

[Fleetmon]

Blown between cyl's 1 & 3 and 5 & 7.

I doubt that's the only problem here but this has to be done first.

 

[moklock]

Check between the injectors on the TBI unit for signs of fuel seepage from the pressure regulator diaphragm also. Had to redo the TBI on my dads old 4.3L for the same symptoms once.

 

[mattd]

i'd be very surprised if it lost compression like that in 16k miles. The oil sounds like it was restoring fuel wash. Do those cylinders have good, consistent spark? An inline spark tester is a useful tool. The backfiring, etc does sound like a timing issue. I too have never seen a 5.7 jump time. Usually it will throw cam/crank sync codes before that happens. Are there any trouble codes stored?

 

[Fleetmon]

I appreciate all the help folks and mattd wins for the proper diagnosis related to fuel wash...I squirted a tad of oil (Rotella TTT) in the LS cylinders and it brought the numbers up except for #'s 1 & 3 (100 w/oil & 130 w/oil). Even cylinders were tested dry (140+).

Grandson is heading north now to start cleaning parts although it's more of a gasket scraping since the parts are so clean. He uses Mobil 1, 5W30 and AC filters. Internally, this engine is clean!

Along with the gasket set, I also bought spark module, cap, and rotor...might as well!

 

[Fleetmon]

When cleaning the cylinder head, I poured kerosene in each port and #'s 1 and 5 poured through the intake valves. Cylinder #'s 3 and 7 held (actually overnight). My local machine shop (Leedy's Automotive, Thomasville Pa...outstanding service!) confirmed badly bent/warped valves. Delane fixed me up with two recon used heads he had laying around.

I was very disappointed to see the quality of the parts used in the head....(.050") oversize valve stems, UGLY looking seats, and three different exhaust valves. I thought Jasper was one of the best?? His mother bought this engine on my recommendation and, although until now, has ran perfectly with fuel mileage around 16 MPG which I feel indicates a healthy engine.

Engine oil/filter: Mobil 1 5w30/Purolator

Although compression was good on the RB, I felt it best to replace that head also...glad I did since #4 intake was leaking kero....a quick spin in the drill press confirmed a slight warp and blackened seat.